TOMOYO Linux Cross Reference
Linux/mm/hugetlb.c

   /*
    * Generic hugetlb support.
    * (C) Nadia Yvette Chambers, April 2004
    */
   #include <linux/list.h>
   #include <linux/init.h>
   #include <linux/module.h>
   #include <linux/mm.h>
   #include <linux/seq_file.h>
  #include <linux/sysctl.h>
  #include <linux/highmem.h>
  #include <linux/mmu_notifier.h>
  #include <linux/nodemask.h>
  #include <linux/pagemap.h>
  #include <linux/mempolicy.h>
  #include <linux/cpuset.h>
  #include <linux/mutex.h>
  #include <linux/bootmem.h>
  #include <linux/sysfs.h>
  #include <linux/slab.h>
  #include <linux/rmap.h>
  #include <linux/swap.h>
  #include <linux/swapops.h>
  #include <linux/page-isolation.h>
  
  #include <asm/page.h>
  #include <asm/pgtable.h>
  #include <asm/tlb.h>
  
  #include <linux/io.h>
  #include <linux/hugetlb.h>
  #include <linux/hugetlb_cgroup.h>
  #include <linux/node.h>
  #include "internal.h"
  
  const unsigned long hugetlb_zero = 0, hugetlb_infinity = ~0UL;
  static gfp_t htlb_alloc_mask = GFP_HIGHUSER;
  unsigned long hugepages_treat_as_movable;
  
  int hugetlb_max_hstate __read_mostly;
  unsigned int default_hstate_idx;
  struct hstate hstates[HUGE_MAX_HSTATE];
  
  __initdata LIST_HEAD(huge_boot_pages);
  
  /* for command line parsing */
  static struct hstate * __initdata parsed_hstate;
  static unsigned long __initdata default_hstate_max_huge_pages;
  static unsigned long __initdata default_hstate_size;
  
  /*
   * Protects updates to hugepage_freelists, nr_huge_pages, and free_huge_pages
   */
  DEFINE_SPINLOCK(hugetlb_lock);
  
  static inline void unlock_or_release_subpool(struct hugepage_subpool *spool)
  {
          bool free = (spool->count == 0) && (spool->used_hpages == 0);
  
          spin_unlock(&spool->lock);
  
          /* If no pages are used, and no other handles to the subpool
           * remain, free the subpool the subpool remain */
          if (free)
                  kfree(spool);
  }
  
  struct hugepage_subpool *hugepage_new_subpool(long nr_blocks)
  {
          struct hugepage_subpool *spool;
  
          spool = kmalloc(sizeof(*spool), GFP_KERNEL);
          if (!spool)
                  return NULL;
  
          spin_lock_init(&spool->lock);
          spool->count = 1;
          spool->max_hpages = nr_blocks;
          spool->used_hpages = 0;
  
          return spool;
  }
  
  void hugepage_put_subpool(struct hugepage_subpool *spool)
  {
          spin_lock(&spool->lock);
          BUG_ON(!spool->count);
          spool->count--;
          unlock_or_release_subpool(spool);
  }
  
  static int hugepage_subpool_get_pages(struct hugepage_subpool *spool,
                                        long delta)
  {
          int ret = 0;
  
          if (!spool)
                  return 0;
  
         spin_lock(&spool->lock);
         if ((spool->used_hpages + delta) <= spool->max_hpages) {
                 spool->used_hpages += delta;
         } else {
                 ret = -ENOMEM;
         }
         spin_unlock(&spool->lock);
 
         return ret;
 }
 
 static void hugepage_subpool_put_pages(struct hugepage_subpool *spool,
                                        long delta)
 {
         if (!spool)
                 return;
 
         spin_lock(&spool->lock);
         spool->used_hpages -= delta;
         /* If hugetlbfs_put_super couldn't free spool due to
         * an outstanding quota reference, free it now. */
         unlock_or_release_subpool(spool);
 }
 
 static inline struct hugepage_subpool *subpool_inode(struct inode *inode)
 {
         return HUGETLBFS_SB(inode->i_sb)->spool;
 }
 
 static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
 {
         return subpool_inode(file_inode(vma->vm_file));
 }
 
 /*
  * Region tracking -- allows tracking of reservations and instantiated pages
  *                    across the pages in a mapping.
  *
  * The region data structures are protected by a combination of the mmap_sem
  * and the hugetlb_instantion_mutex.  To access or modify a region the caller
  * must either hold the mmap_sem for write, or the mmap_sem for read and
  * the hugetlb_instantiation mutex:
  *
  *      down_write(&mm->mmap_sem);
  * or
  *      down_read(&mm->mmap_sem);
  *      mutex_lock(&hugetlb_instantiation_mutex);
  */
 struct file_region {
         struct list_head link;
         long from;
         long to;
 };
 
 static long region_add(struct list_head *head, long f, long t)
 {
         struct file_region *rg, *nrg, *trg;
 
         /* Locate the region we are either in or before. */
         list_for_each_entry(rg, head, link)
                 if (f <= rg->to)
                         break;
 
         /* Round our left edge to the current segment if it encloses us. */
         if (f > rg->from)
                 f = rg->from;
 
         /* Check for and consume any regions we now overlap with. */
         nrg = rg;
         list_for_each_entry_safe(rg, trg, rg->link.prev, link) {
                 if (&rg->link == head)
                         break;
                 if (rg->from > t)
                         break;
 
                 /* If this area reaches higher then extend our area to
                  * include it completely.  If this is not the first area
                  * which we intend to reuse, free it. */
                 if (rg->to > t)
                         t = rg->to;
                 if (rg != nrg) {
                         list_del(&rg->link);
                         kfree(rg);
                 }
         }
         nrg->from = f;
         nrg->to = t;
         return 0;
 }
 
 static long region_chg(struct list_head *head, long f, long t)
 {
         struct file_region *rg, *nrg;
         long chg = 0;
 
         /* Locate the region we are before or in. */
         list_for_each_entry(rg, head, link)
                 if (f <= rg->to)
                         break;
 
         /* If we are below the current region then a new region is required.
          * Subtle, allocate a new region at the position but make it zero
          * size such that we can guarantee to record the reservation. */
         if (&rg->link == head || t < rg->from) {
                 nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
                 if (!nrg)
                         return -ENOMEM;
                 nrg->from = f;
                 nrg->to   = f;
                 INIT_LIST_HEAD(&nrg->link);
                 list_add(&nrg->link, rg->link.prev);
 
                 return t - f;
         }
 
         /* Round our left edge to the current segment if it encloses us. */
         if (f > rg->from)
                 f = rg->from;
         chg = t - f;
 
         /* Check for and consume any regions we now overlap with. */
         list_for_each_entry(rg, rg->link.prev, link) {
                 if (&rg->link == head)
                         break;
                 if (rg->from > t)
                         return chg;
 
                 /* We overlap with this area, if it extends further than
                  * us then we must extend ourselves.  Account for its
                  * existing reservation. */
                 if (rg->to > t) {
                         chg += rg->to - t;
                         t = rg->to;
                 }
                 chg -= rg->to - rg->from;
         }
         return chg;
 }
 
 static long region_truncate(struct list_head *head, long end)
 {
         struct file_region *rg, *trg;
         long chg = 0;
 
         /* Locate the region we are either in or before. */
         list_for_each_entry(rg, head, link)
                 if (end <= rg->to)
                         break;
         if (&rg->link == head)
                 return 0;
 
         /* If we are in the middle of a region then adjust it. */
         if (end > rg->from) {
                 chg = rg->to - end;
                 rg->to = end;
                 rg = list_entry(rg->link.next, typeof(*rg), link);
         }
 
         /* Drop any remaining regions. */
         list_for_each_entry_safe(rg, trg, rg->link.prev, link) {
                 if (&rg->link == head)
                         break;
                 chg += rg->to - rg->from;
                 list_del(&rg->link);
                 kfree(rg);
         }
         return chg;
 }
 
 static long region_count(struct list_head *head, long f, long t)
 {
         struct file_region *rg;
         long chg = 0;
 
         /* Locate each segment we overlap with, and count that overlap. */
         list_for_each_entry(rg, head, link) {
                 long seg_from;
                 long seg_to;
 
                 if (rg->to <= f)
                         continue;
                 if (rg->from >= t)
                         break;
 
                 seg_from = max(rg->from, f);
                 seg_to = min(rg->to, t);
 
                 chg += seg_to - seg_from;
         }
 
         return chg;
 }
 
 /*
  * Convert the address within this vma to the page offset within
  * the mapping, in pagecache page units; huge pages here.
  */
 static pgoff_t vma_hugecache_offset(struct hstate *h,
                         struct vm_area_struct *vma, unsigned long address)
 {
         return ((address - vma->vm_start) >> huge_page_shift(h)) +
                         (vma->vm_pgoff >> huge_page_order(h));
 }
 
 pgoff_t linear_hugepage_index(struct vm_area_struct *vma,
                                      unsigned long address)
 {
         return vma_hugecache_offset(hstate_vma(vma), vma, address);
 }
 
 /*
  * Return the size of the pages allocated when backing a VMA. In the majority
  * cases this will be same size as used by the page table entries.
  */
 unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
 {
         struct hstate *hstate;
 
         if (!is_vm_hugetlb_page(vma))
                 return PAGE_SIZE;
 
         hstate = hstate_vma(vma);
 
         return 1UL << (hstate->order + PAGE_SHIFT);
 }
 EXPORT_SYMBOL_GPL(vma_kernel_pagesize);
 
 /*
  * Return the page size being used by the MMU to back a VMA. In the majority
  * of cases, the page size used by the kernel matches the MMU size. On
  * architectures where it differs, an architecture-specific version of this
  * function is required.
  */
 #ifndef vma_mmu_pagesize
 unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
 {
         return vma_kernel_pagesize(vma);
 }
 #endif
 
 /*
  * Flags for MAP_PRIVATE reservations.  These are stored in the bottom
  * bits of the reservation map pointer, which are always clear due to
  * alignment.
  */
 #define HPAGE_RESV_OWNER    (1UL << 0)
 #define HPAGE_RESV_UNMAPPED (1UL << 1)
 #define HPAGE_RESV_MASK (HPAGE_RESV_OWNER | HPAGE_RESV_UNMAPPED)
 
 /*
  * These helpers are used to track how many pages are reserved for
  * faults in a MAP_PRIVATE mapping. Only the process that called mmap()
  * is guaranteed to have their future faults succeed.
  *
  * With the exception of reset_vma_resv_huge_pages() which is called at fork(),
  * the reserve counters are updated with the hugetlb_lock held. It is safe
  * to reset the VMA at fork() time as it is not in use yet and there is no
  * chance of the global counters getting corrupted as a result of the values.
  *
  * The private mapping reservation is represented in a subtly different
  * manner to a shared mapping.  A shared mapping has a region map associated
  * with the underlying file, this region map represents the backing file
  * pages which have ever had a reservation assigned which this persists even
  * after the page is instantiated.  A private mapping has a region map
  * associated with the original mmap which is attached to all VMAs which
  * reference it, this region map represents those offsets which have consumed
  * reservation ie. where pages have been instantiated.
  */
 static unsigned long get_vma_private_data(struct vm_area_struct *vma)
 {
         return (unsigned long)vma->vm_private_data;
 }
 
 static void set_vma_private_data(struct vm_area_struct *vma,
                                                         unsigned long value)
 {
         vma->vm_private_data = (void *)value;
 }
 
 struct resv_map {
         struct kref refs;
         struct list_head regions;
 };
 
 static struct resv_map *resv_map_alloc(void)
 {
         struct resv_map *resv_map = kmalloc(sizeof(*resv_map), GFP_KERNEL);
         if (!resv_map)
                 return NULL;
 
         kref_init(&resv_map->refs);
         INIT_LIST_HEAD(&resv_map->regions);
 
         return resv_map;
 }
 
 static void resv_map_release(struct kref *ref)
 {
         struct resv_map *resv_map = container_of(ref, struct resv_map, refs);
 
         /* Clear out any active regions before we release the map. */
         region_truncate(&resv_map->regions, 0);
         kfree(resv_map);
 }
 
 static struct resv_map *vma_resv_map(struct vm_area_struct *vma)
 {
         VM_BUG_ON(!is_vm_hugetlb_page(vma));
         if (!(vma->vm_flags & VM_MAYSHARE))
                 return (struct resv_map *)(get_vma_private_data(vma) &
                                                         ~HPAGE_RESV_MASK);
         return NULL;
 }
 
 static void set_vma_resv_map(struct vm_area_struct *vma, struct resv_map *map)
 {
         VM_BUG_ON(!is_vm_hugetlb_page(vma));
         VM_BUG_ON(vma->vm_flags & VM_MAYSHARE);
 
         set_vma_private_data(vma, (get_vma_private_data(vma) &
                                 HPAGE_RESV_MASK) | (unsigned long)map);
 }
 
 static void set_vma_resv_flags(struct vm_area_struct *vma, unsigned long flags)
 {
         VM_BUG_ON(!is_vm_hugetlb_page(vma));
         VM_BUG_ON(vma->vm_flags & VM_MAYSHARE);
 
         set_vma_private_data(vma, get_vma_private_data(vma) | flags);
 }
 
 static int is_vma_resv_set(struct vm_area_struct *vma, unsigned long flag)
 {
         VM_BUG_ON(!is_vm_hugetlb_page(vma));
 
         return (get_vma_private_data(vma) & flag) != 0;
 }
 
 /* Decrement the reserved pages in the hugepage pool by one */
 static void decrement_hugepage_resv_vma(struct hstate *h,
                         struct vm_area_struct *vma)
 {
         if (vma->vm_flags & VM_NORESERVE)
                 return;
 
         if (vma->vm_flags & VM_MAYSHARE) {
                 /* Shared mappings always use reserves */
                 h->resv_huge_pages--;
         } else if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
                 /*
                  * Only the process that called mmap() has reserves for
                  * private mappings.
                  */
                 h->resv_huge_pages--;
         }
 }
 
 /* Reset counters to 0 and clear all HPAGE_RESV_* flags */
 void reset_vma_resv_huge_pages(struct vm_area_struct *vma)
 {
         VM_BUG_ON(!is_vm_hugetlb_page(vma));
         if (!(vma->vm_flags & VM_MAYSHARE))
                 vma->vm_private_data = (void *)0;
 }
 
 /* Returns true if the VMA has associated reserve pages */
 static int vma_has_reserves(struct vm_area_struct *vma)
 {
         if (vma->vm_flags & VM_MAYSHARE)
                 return 1;
         if (is_vma_resv_set(vma, HPAGE_RESV_OWNER))
                 return 1;
         return 0;
 }
 
 static void copy_gigantic_page(struct page *dst, struct page *src)
 {
         int i;
         struct hstate *h = page_hstate(src);
         struct page *dst_base = dst;
         struct page *src_base = src;
 
         for (i = 0; i < pages_per_huge_page(h); ) {
                 cond_resched();
                 copy_highpage(dst, src);
 
                 i++;
                 dst = mem_map_next(dst, dst_base, i);
                 src = mem_map_next(src, src_base, i);
         }
 }
 
 void copy_huge_page(struct page *dst, struct page *src)
 {
         int i;
         struct hstate *h = page_hstate(src);
 
         if (unlikely(pages_per_huge_page(h) > MAX_ORDER_NR_PAGES)) {
                 copy_gigantic_page(dst, src);
                 return;
         }
 
         might_sleep();
         for (i = 0; i < pages_per_huge_page(h); i++) {
                 cond_resched();
                 copy_highpage(dst + i, src + i);
         }
 }
 
 static void enqueue_huge_page(struct hstate *h, struct page *page)
 {
         int nid = page_to_nid(page);
         list_move(&page->lru, &h->hugepage_freelists[nid]);
         h->free_huge_pages++;
         h->free_huge_pages_node[nid]++;
 }
 
 static struct page *dequeue_huge_page_node(struct hstate *h, int nid)
 {
         struct page *page;
 
         list_for_each_entry(page, &h->hugepage_freelists[nid], lru)
                 if (!is_migrate_isolate_page(page))
                         break;
         /*
          * if 'non-isolated free hugepage' not found on the list,
          * the allocation fails.
          */
         if (&h->hugepage_freelists[nid] == &page->lru)
                 return NULL;
         list_move(&page->lru, &h->hugepage_activelist);
         set_page_refcounted(page);
         h->free_huge_pages--;
         h->free_huge_pages_node[nid]--;
         return page;
 }
 
 static struct page *dequeue_huge_page_vma(struct hstate *h,
                                 struct vm_area_struct *vma,
                                 unsigned long address, int avoid_reserve)
 {
         struct page *page = NULL;
         struct mempolicy *mpol;
         nodemask_t *nodemask;
         struct zonelist *zonelist;
         struct zone *zone;
         struct zoneref *z;
         unsigned int cpuset_mems_cookie;
 
 retry_cpuset:
         cpuset_mems_cookie = get_mems_allowed();
         zonelist = huge_zonelist(vma, address,
                                         htlb_alloc_mask, &mpol, &nodemask);
         /*
          * A child process with MAP_PRIVATE mappings created by their parent
          * have no page reserves. This check ensures that reservations are
          * not "stolen". The child may still get SIGKILLed
          */
         if (!vma_has_reserves(vma) &&
                         h->free_huge_pages - h->resv_huge_pages == 0)
                 goto err;
 
         /* If reserves cannot be used, ensure enough pages are in the pool */
         if (avoid_reserve && h->free_huge_pages - h->resv_huge_pages == 0)
                 goto err;
 
         for_each_zone_zonelist_nodemask(zone, z, zonelist,
                                                 MAX_NR_ZONES - 1, nodemask) {
                 if (cpuset_zone_allowed_softwall(zone, htlb_alloc_mask)) {
                         page = dequeue_huge_page_node(h, zone_to_nid(zone));
                         if (page) {
                                 if (!avoid_reserve)
                                         decrement_hugepage_resv_vma(h, vma);
                                 break;
                         }
                 }
         }
 
         mpol_cond_put(mpol);
         if (unlikely(!put_mems_allowed(cpuset_mems_cookie) && !page))
                 goto retry_cpuset;
         return page;
 
 err:
         mpol_cond_put(mpol);
         return NULL;
 }
 
 static void update_and_free_page(struct hstate *h, struct page *page)
 {
         int i;
 
         VM_BUG_ON(h->order >= MAX_ORDER);
 
         h->nr_huge_pages--;
         h->nr_huge_pages_node[page_to_nid(page)]--;
         for (i = 0; i < pages_per_huge_page(h); i++) {
                 page[i].flags &= ~(1 << PG_locked | 1 << PG_error |
                                 1 << PG_referenced | 1 << PG_dirty |
                                 1 << PG_active | 1 << PG_reserved |
                                 1 << PG_private | 1 << PG_writeback);
         }
         VM_BUG_ON(hugetlb_cgroup_from_page(page));
         set_compound_page_dtor(page, NULL);
         set_page_refcounted(page);
         arch_release_hugepage(page);
         __free_pages(page, huge_page_order(h));
 }
 
 struct hstate *size_to_hstate(unsigned long size)
 {
         struct hstate *h;
 
         for_each_hstate(h) {
                 if (huge_page_size(h) == size)
                         return h;
         }
         return NULL;
 }
 
 static void free_huge_page(struct page *page)
 {
         /*
          * Can't pass hstate in here because it is called from the
          * compound page destructor.
          */
         struct hstate *h = page_hstate(page);
         int nid = page_to_nid(page);
         struct hugepage_subpool *spool =
                 (struct hugepage_subpool *)page_private(page);
 
         set_page_private(page, 0);
         page->mapping = NULL;
         BUG_ON(page_count(page));
         BUG_ON(page_mapcount(page));
 
         spin_lock(&hugetlb_lock);
         hugetlb_cgroup_uncharge_page(hstate_index(h),
                                      pages_per_huge_page(h), page);
         if (h->surplus_huge_pages_node[nid] && huge_page_order(h) < MAX_ORDER) {
                 /* remove the page from active list */
                 list_del(&page->lru);
                 update_and_free_page(h, page);
                 h->surplus_huge_pages--;
                 h->surplus_huge_pages_node[nid]--;
         } else {
                 arch_clear_hugepage_flags(page);
                 enqueue_huge_page(h, page);
         }
         spin_unlock(&hugetlb_lock);
         hugepage_subpool_put_pages(spool, 1);
 }
 
 static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
 {
         INIT_LIST_HEAD(&page->lru);
         set_compound_page_dtor(page, free_huge_page);
         spin_lock(&hugetlb_lock);
         set_hugetlb_cgroup(page, NULL);
         h->nr_huge_pages++;
         h->nr_huge_pages_node[nid]++;
         spin_unlock(&hugetlb_lock);
         put_page(page); /* free it into the hugepage allocator */
 }
 
 static void prep_compound_gigantic_page(struct page *page, unsigned long order)
 {
         int i;
         int nr_pages = 1 << order;
         struct page *p = page + 1;
 
         /* we rely on prep_new_huge_page to set the destructor */
         set_compound_order(page, order);
         __SetPageHead(page);
         for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) {
                 __SetPageTail(p);
                 set_page_count(p, 0);
                 p->first_page = page;
         }
 }
 
 /*
  * PageHuge() only returns true for hugetlbfs pages, but not for normal or
  * transparent huge pages.  See the PageTransHuge() documentation for more
  * details.
  */
 int PageHuge(struct page *page)
 {
         compound_page_dtor *dtor;
 
         if (!PageCompound(page))
                 return 0;
 
         page = compound_head(page);
         dtor = get_compound_page_dtor(page);
 
         return dtor == free_huge_page;
 }
 EXPORT_SYMBOL_GPL(PageHuge);
 
 /*
  * PageHeadHuge() only returns true for hugetlbfs head page, but not for
  * normal or transparent huge pages.
  */
 int PageHeadHuge(struct page *page_head)
 {
         compound_page_dtor *dtor;
 
         if (!PageHead(page_head))
                 return 0;
 
         dtor = get_compound_page_dtor(page_head);
 
         return dtor == free_huge_page;
 }
 EXPORT_SYMBOL_GPL(PageHeadHuge);
 
 pgoff_t __basepage_index(struct page *page)
 {
         struct page *page_head = compound_head(page);
         pgoff_t index = page_index(page_head);
         unsigned long compound_idx;
 
         if (!PageHuge(page_head))
                 return page_index(page);
 
         if (compound_order(page_head) >= MAX_ORDER)
                 compound_idx = page_to_pfn(page) - page_to_pfn(page_head);
         else
                 compound_idx = page - page_head;
 
         return (index << compound_order(page_head)) + compound_idx;
 }
 
 static struct page *alloc_fresh_huge_page_node(struct hstate *h, int nid)
 {
         struct page *page;
 
         if (h->order >= MAX_ORDER)
                 return NULL;
 
         page = alloc_pages_exact_node(nid,
                 htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|
                                                 __GFP_REPEAT|__GFP_NOWARN,
                 huge_page_order(h));
         if (page) {
                 if (arch_prepare_hugepage(page)) {
                         __free_pages(page, huge_page_order(h));
                         return NULL;
                 }
                 prep_new_huge_page(h, page, nid);
         }
 
         return page;
 }
 
 /*
  * common helper functions for hstate_next_node_to_{alloc|free}.
  * We may have allocated or freed a huge page based on a different
  * nodes_allowed previously, so h->next_node_to_{alloc|free} might
  * be outside of *nodes_allowed.  Ensure that we use an allowed
  * node for alloc or free.
  */
 static int next_node_allowed(int nid, nodemask_t *nodes_allowed)
 {
         nid = next_node(nid, *nodes_allowed);
         if (nid == MAX_NUMNODES)
                 nid = first_node(*nodes_allowed);
         VM_BUG_ON(nid >= MAX_NUMNODES);
 
         return nid;
 }
 
 static int get_valid_node_allowed(int nid, nodemask_t *nodes_allowed)
 {
         if (!node_isset(nid, *nodes_allowed))
                 nid = next_node_allowed(nid, nodes_allowed);
         return nid;
 }
 
 /*
  * returns the previously saved node ["this node"] from which to
  * allocate a persistent huge page for the pool and advance the
  * next node from which to allocate, handling wrap at end of node
  * mask.
  */
 static int hstate_next_node_to_alloc(struct hstate *h,
                                         nodemask_t *nodes_allowed)
 {
         int nid;
 
         VM_BUG_ON(!nodes_allowed);
 
         nid = get_valid_node_allowed(h->next_nid_to_alloc, nodes_allowed);
         h->next_nid_to_alloc = next_node_allowed(nid, nodes_allowed);
 
         return nid;
 }
 
 static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
 {
         struct page *page;
         int start_nid;
         int next_nid;
         int ret = 0;
 
         start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
         next_nid = start_nid;
 
         do {
                 page = alloc_fresh_huge_page_node(h, next_nid);
                 if (page) {
                         ret = 1;
                         break;
                 }
                 next_nid = hstate_next_node_to_alloc(h, nodes_allowed);
         } while (next_nid != start_nid);
 
         if (ret)
                 count_vm_event(HTLB_BUDDY_PGALLOC);
         else
                 count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
 
         return ret;
 }
 
 /*
  * helper for free_pool_huge_page() - return the previously saved
  * node ["this node"] from which to free a huge page.  Advance the
  * next node id whether or not we find a free huge page to free so
  * that the next attempt to free addresses the next node.
  */
 static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
 {
         int nid;
 
         VM_BUG_ON(!nodes_allowed);
 
         nid = get_valid_node_allowed(h->next_nid_to_free, nodes_allowed);
         h->next_nid_to_free = next_node_allowed(nid, nodes_allowed);
 
         return nid;
 }
 
 /*
  * Free huge page from pool from next node to free.
  * Attempt to keep persistent huge pages more or less
  * balanced over allowed nodes.
  * Called with hugetlb_lock locked.
  */
 static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
                                                          bool acct_surplus)
 {
         int start_nid;
         int next_nid;
         int ret = 0;
 
         start_nid = hstate_next_node_to_free(h, nodes_allowed);
         next_nid = start_nid;
 
         do {
                 /*
                  * If we're returning unused surplus pages, only examine
                  * nodes with surplus pages.
                  */
                 if ((!acct_surplus || h->surplus_huge_pages_node[next_nid]) &&
                     !list_empty(&h->hugepage_freelists[next_nid])) {
                         struct page *page =
                                 list_entry(h->hugepage_freelists[next_nid].next,
                                           struct page, lru);
                         list_del(&page->lru);
                         h->free_huge_pages--;
                         h->free_huge_pages_node[next_nid]--;
                         if (acct_surplus) {
                                 h->surplus_huge_pages--;
                                 h->surplus_huge_pages_node[next_nid]--;
                         }
                         update_and_free_page(h, page);
                         ret = 1;
                         break;
                 }
                 next_nid = hstate_next_node_to_free(h, nodes_allowed);
         } while (next_nid != start_nid);
 
         return ret;
 }
 
 static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
 {
         struct page *page;
         unsigned int r_nid;
 
         if (h->order >= MAX_ORDER)
                 return NULL;
 
         /*
          * Assume we will successfully allocate the surplus page to
          * prevent racing processes from causing the surplus to exceed
          * overcommit
          *
          * This however introduces a different race, where a process B
          * tries to grow the static hugepage pool while alloc_pages() is
          * called by process A. B will only examine the per-node
          * counters in determining if surplus huge pages can be
          * converted to normal huge pages in adjust_pool_surplus(). A
          * won't be able to increment the per-node counter, until the
          * lock is dropped by B, but B doesn't drop hugetlb_lock until
          * no more huge pages can be converted from surplus to normal
          * state (and doesn't try to convert again). Thus, we have a
          * case where a surplus huge page exists, the pool is grown, and
          * the surplus huge page still exists after, even though it
          * should just have been converted to a normal huge page. This
          * does not leak memory, though, as the hugepage will be freed
          * once it is out of use. It also does not allow the counters to
          * go out of whack in adjust_pool_surplus() as we don't modify
          * the node values until we've gotten the hugepage and only the
          * per-node value is checked there.
          */
         spin_lock(&hugetlb_lock);
         if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) {
                 spin_unlock(&hugetlb_lock);
                 return NULL;
         } else {
                 h->nr_huge_pages++;
                 h->surplus_huge_pages++;
         }
         spin_unlock(&hugetlb_lock);
 
         if (nid == NUMA_NO_NODE)
                 page = alloc_pages(htlb_alloc_mask|__GFP_COMP|
                                    __GFP_REPEAT|__GFP_NOWARN,
                                    huge_page_order(h));
         else
                 page = alloc_pages_exact_node(nid,
                         htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|
                         __GFP_REPEAT|__GFP_NOWARN, huge_page_order(h));
 
         if (page && arch_prepare_hugepage(page)) {
                 __free_pages(page, huge_page_order(h));
                 page = NULL;
         }
 
         spin_lock(&hugetlb_lock);
         if (page) {
                 INIT_LIST_HEAD(&page->lru);
                 r_nid = page_to_nid(page);
                 set_compound_page_dtor(page, free_huge_page);
                 set_hugetlb_cgroup(page, NULL);
                 /*
                  * We incremented the global counters already
                  */
                 h->nr_huge_pages_node[r_nid]++;
                 h->surplus_huge_pages_node[r_nid]++;
                 __count_vm_event(HTLB_BUDDY_PGALLOC);
         } else {
                 h->nr_huge_pages--;
                 h->surplus_huge_pages--;
                 __count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
         }
         spin_unlock(&hugetlb_lock);
 
         return page;
 }
 
 /*
  * This allocation function is useful in the context where vma is irrelevant.
  * E.g. soft-offlining uses this function because it only cares physical
  * address of error page.
  */
 struct page *alloc_huge_page_node(struct hstate *h, int nid)
 {
         struct page *page;
 
         spin_lock(&hugetlb_lock);
         page = dequeue_huge_page_node(h, nid);
         spin_unlock(&hugetlb_lock);
 
         if (!page)
                 page = alloc_buddy_huge_page(h, nid);
 
         return page;
 }
 
 /*
  * Increase the hugetlb pool such that it can accommodate a reservation
  * of size 'delta'.
  */
 static int gather_surplus_pages(struct hstate *h, int delta)
 {
         struct list_head surplus_list;
         struct page *page, *tmp;
         int ret, i;
         int needed, allocated;
         bool alloc_ok = true;
 
         needed = (h->resv_huge_pages + delta) - h->free_huge_pages;
         if (needed <= 0) {
                 h->resv_huge_pages += delta;
                 return 0;
         }
 
         allocated = 0;
         INIT_LIST_HEAD(&surplus_list);
 
         ret = -ENOMEM;
 retry:
         spin_unlock(&hugetlb_lock);
         for (i = 0; i < needed; i++) {
                 page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
                 if (!page) {
                         alloc_ok = false;
                         break;
                 }
                 list_add(&page->lru, &surplus_list);
         }
         allocated += i;
 
         /*
          * After retaking hugetlb_lock, we need to recalculate 'needed'
          * because either resv_huge_pages or free_huge_pages may have changed.
          */
         spin_lock(&hugetlb_lock);
         needed = (h->resv_huge_pages + delta) -
                         (h->free_huge_pages + allocated);
         if (needed > 0) {
                 if (alloc_ok)
                         goto retry;
                 /*
                  * We were not able to allocate enough pages to
                  * satisfy the entire reservation so we free what
                  * we've allocated so far.
                  */
                 goto free;
         }
         /*
          * The surplus_list now contains _at_least_ the number of extra pages
          * needed to accommodate the reservation.  Add the appropriate number
          * of pages to the hugetlb pool and free the extras back to the buddy
          * allocator.  Commit the entire reservation here to prevent another
          * process from stealing the pages as they are added to the pool but
          * before they are reserved.
          */
         needed += allocated;
         h->resv_huge_pages += delta;
         ret = 0;
 
         /* Free the needed pages to the hugetlb pool */
         list_for_each_entry_safe(page, tmp, &surplus_list, lru) {
                 if ((--needed) < 0)
                         break;
                 /*
                  * This page is now managed by the hugetlb allocator and has
                  * no users -- drop the buddy allocator's reference.
                  */
                 put_page_testzero(page);
                 VM_BUG_ON(page_count(page));
                 enqueue_huge_page(h, page);
         }
 free:
         spin_unlock(&hugetlb_lock);
 
         /* Free unnecessary surplus pages to the buddy allocator */
         if (!list_empty(&surplus_list)) {
                 list_for_each_entry_safe(page, tmp, &surplus_list, lru) {
                         put_page(page);
                 }
         }
         spin_lock(&hugetlb_lock);
 
         return ret;
 }
 
 /*
  * This routine has two main purposes:
  * 1) Decrement the reservation count (resv_huge_pages) by the value passed
  *    in unused_resv_pages.  This corresponds to the prior adjustments made
  *    to the associated reservation map.
  * 2) Free any unused surplus pages that may have been allocated to satisfy
  *    the reservation.  As many as unused_resv_pages may be freed.
  *
  * Called with hugetlb_lock held.  However, the lock could be dropped (and
  * reacquired) during calls to cond_resched_lock.  Whenever dropping the lock,
  * we must make sure nobody else can claim pages we are in the process of
  * freeing.  Do this by ensuring resv_huge_page always is greater than the
  * number of huge pages we plan to free when dropping the lock.
  */
 static void return_unused_surplus_pages(struct hstate *h,
                                         unsigned long unused_resv_pages)
 {
         unsigned long nr_pages;
 
         /* Cannot return gigantic pages currently */
         if (h->order >= MAX_ORDER)
                 goto out;
 
         /*
          * Part (or even all) of the reservation could have been backed
          * by pre-allocated pages. Only free surplus pages.
          */
         nr_pages = min(unused_resv_pages, h->surplus_huge_pages);
 
         /*
          * We want to release as many surplus pages as possible, spread
          * evenly across all nodes with memory. Iterate across these nodes
          * until we can no longer free unreserved surplus pages. This occurs
          * when the nodes with surplus pages have no free pages.
          * free_pool_huge_page() will balance the the freed pages across the
          * on-line nodes with memory and will handle the hstate accounting.
          *
          * Note that we decrement resv_huge_pages as we free the pages.  If
          * we drop the lock, resv_huge_pages will still be sufficiently large
          * to cover subsequent pages we may free.
          */
         while (nr_pages--) {
                 h->resv_huge_pages--;
                 unused_resv_pages--;
                 if (!free_pool_huge_page(h, &node_states[N_MEMORY], 1))
                         goto out;
                 cond_resched_lock(&hugetlb_lock);
         }
 
 out:
         /* Fully uncommit the reservation */
         h->resv_huge_pages -= unused_resv_pages;
 }
 
 /*
  * Determine if the huge page at addr within the vma has an associated
  * reservation.  Where it does not we will need to logically increase
  * reservation and actually increase subpool usage before an allocation
  * can occur.  Where any new reservation would be required the
  * reservation change is prepared, but not committed.  Once the page
  * has been allocated from the subpool and instantiated the change should
  * be committed via vma_commit_reservation.  No action is required on
  * failure.
  */
 static long vma_needs_reservation(struct hstate *h,
                         struct vm_area_struct *vma, unsigned long addr)
 {
         struct address_space *mapping = vma->vm_file->f_mapping;
         struct inode *inode = mapping->host;
 
         if (vma->vm_flags & VM_MAYSHARE) {
                 pgoff_t idx = vma_hugecache_offset(h, vma, addr);
                 return region_chg(&inode->i_mapping->private_list,
                                                         idx, idx + 1);
 
         } else if (!is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
                 return 1;
 
         } else  {
                 long err;
                 pgoff_t idx = vma_hugecache_offset(h, vma, addr);
                 struct resv_map *reservations = vma_resv_map(vma);
 
                 err = region_chg(&reservations->regions, idx, idx + 1);
                 if (err < 0)
                         return err;
                 return 0;
         }
 }
 static void vma_commit_reservation(struct hstate *h,
                         struct vm_area_struct *vma, unsigned long addr)
 {
         struct address_space *mapping = vma->vm_file->f_mapping;
         struct inode *inode = mapping->host;
 
         if (vma->vm_flags & VM_MAYSHARE) {
                 pgoff_t idx = vma_hugecache_offset(h, vma, addr);
                 region_add(&inode->i_mapping->private_list, idx, idx + 1);
 
         } else if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
                 pgoff_t idx = vma_hugecache_offset(h, vma, addr);
                 struct resv_map *reservations = vma_resv_map(vma);
 
                 /* Mark this page used in the map. */
                 region_add(&reservations->regions, idx, idx + 1);
         }
 }
 
 static struct page *alloc_huge_page(struct vm_area_struct *vma,
                                     unsigned long addr, int avoid_reserve)
 {
         struct hugepage_subpool *spool = subpool_vma(vma);
         struct hstate *h = hstate_vma(vma);
         struct page *page;
         long chg;
         int ret, idx;
         struct hugetlb_cgroup *h_cg;
 
         idx = hstate_index(h);
         /*
          * Processes that did not create the mapping will have no
          * reserves and will not have accounted against subpool
          * limit. Check that the subpool limit can be made before
          * satisfying the allocation MAP_NORESERVE mappings may also
          * need pages and subpool limit allocated allocated if no reserve
          * mapping overlaps.
          */
         chg = vma_needs_reservation(h, vma, addr);
         if (chg < 0)
                 return ERR_PTR(-ENOMEM);
         if (chg)
                 if (hugepage_subpool_get_pages(spool, chg))
                         return ERR_PTR(-ENOSPC);
 
         ret = hugetlb_cgroup_charge_cgroup(idx, pages_per_huge_page(h), &h_cg);
         if (ret) {
                 hugepage_subpool_put_pages(spool, chg);
                 return ERR_PTR(-ENOSPC);
         }
         spin_lock(&hugetlb_lock);
         page = dequeue_huge_page_vma(h, vma, addr, avoid_reserve);
         if (page) {
                 /* update page cgroup details */
                 hugetlb_cgroup_commit_charge(idx, pages_per_huge_page(h),
                                              h_cg, page);
                 spin_unlock(&hugetlb_lock);
         } else {
                 spin_unlock(&hugetlb_lock);
                 page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
                 if (!page) {
                         hugetlb_cgroup_uncharge_cgroup(idx,
                                                        pages_per_huge_page(h),
                                                        h_cg);
                         hugepage_subpool_put_pages(spool, chg);
                         return ERR_PTR(-ENOSPC);
                 }
                 spin_lock(&hugetlb_lock);
                 hugetlb_cgroup_commit_charge(idx, pages_per_huge_page(h),
                                              h_cg, page);
                 list_move(&page->lru, &h->hugepage_activelist);
                 spin_unlock(&hugetlb_lock);
         }
 
         set_page_private(page, (unsigned long)spool);
 
         vma_commit_reservation(h, vma, addr);
         return page;
 }
 
 int __weak alloc_bootmem_huge_page(struct hstate *h)
 {
         struct huge_bootmem_page *m;
         int nr_nodes = nodes_weight(node_states[N_MEMORY]);
 
         while (nr_nodes) {
                 void *addr;
 
                 addr = __alloc_bootmem_node_nopanic(
                                 NODE_DATA(hstate_next_node_to_alloc(h,
                                                 &node_states[N_MEMORY])),
                                 huge_page_size(h), huge_page_size(h), 0);
 
                 if (addr) {
                         /*
                          * Use the beginning of the huge page to store the
                          * huge_bootmem_page struct (until gather_bootmem
                          * puts them into the mem_map).
                          */
                         m = addr;
                         goto found;
                 }
                 nr_nodes--;
         }
         return 0;
 
 found:
         BUG_ON((unsigned long)virt_to_phys(m) & (huge_page_size(h) - 1));
         /* Put them into a private list first because mem_map is not up yet */
         list_add(&m->list, &huge_boot_pages);
         m->hstate = h;
         return 1;
 }
 
 static void prep_compound_huge_page(struct page *page, int order)
 {
         if (unlikely(order > (MAX_ORDER - 1)))
                 prep_compound_gigantic_page(page, order);
         else
                 prep_compound_page(page, order);
 }
 
 /* Put bootmem huge pages into the standard lists after mem_map is up */
 static void __init gather_bootmem_prealloc(void)
 {
         struct huge_bootmem_page *m;
 
         list_for_each_entry(m, &huge_boot_pages, list) {
                 struct hstate *h = m->hstate;
                 struct page *page;
 
 #ifdef CONFIG_HIGHMEM
                 page = pfn_to_page(m->phys >> PAGE_SHIFT);
                 free_bootmem_late((unsigned long)m,
                                   sizeof(struct huge_bootmem_page));
 #else
                 page = virt_to_page(m);
 #endif
                 __ClearPageReserved(page);
                 WARN_ON(page_count(page) != 1);
                 prep_compound_huge_page(page, h->order);
                 prep_new_huge_page(h, page, page_to_nid(page));
                 /*
                  * If we had gigantic hugepages allocated at boot time, we need
                  * to restore the 'stolen' pages to totalram_pages in order to
                  * fix confusing memory reports from free(1) and another
                  * side-effects, like CommitLimit going negative.
                  */
                 if (h->order > (MAX_ORDER - 1))
                         totalram_pages += 1 << h->order;
         }
 }
 
 static void __init hugetlb_hstate_alloc_pages(struct hstate *h)
 {
         unsigned long i;
 
         for (i = 0; i < h->max_huge_pages; ++i) {
                 if (h->order >= MAX_ORDER) {
                         if (!alloc_bootmem_huge_page(h))
                                 break;
                 } else if (!alloc_fresh_huge_page(h,
                                          &node_states[N_MEMORY]))
                         break;
         }
         h->max_huge_pages = i;
 }
 
 static void __init hugetlb_init_hstates(void)
 {
         struct hstate *h;
 
         for_each_hstate(h) {
                 /* oversize hugepages were init'ed in early boot */
                 if (h->order < MAX_ORDER)
                         hugetlb_hstate_alloc_pages(h);
         }
 }
 
 static char * __init memfmt(char *buf, unsigned long n)
 {
         if (n >= (1UL << 30))
                 sprintf(buf, "%lu GB", n >> 30);
         else if (n >= (1UL << 20))
                 sprintf(buf, "%lu MB", n >> 20);
         else
                 sprintf(buf, "%lu KB", n >> 10);
         return buf;
 }
 
 static void __init report_hugepages(void)
 {
         struct hstate *h;
 
         for_each_hstate(h) {
                 char buf[32];
                 pr_info("HugeTLB registered %s page size, pre-allocated %ld pages\n",
                         memfmt(buf, huge_page_size(h)),
                         h->free_huge_pages);
         }
 }
 
 #ifdef CONFIG_HIGHMEM
 static void try_to_free_low(struct hstate *h, unsigned long count,
                                                 nodemask_t *nodes_allowed)
 {
         int i;
 
         if (h->order >= MAX_ORDER)
                 return;
 
         for_each_node_mask(i, *nodes_allowed) {
                 struct page *page, *next;
                 struct list_head *freel = &h->hugepage_freelists[i];
                 list_for_each_entry_safe(page, next, freel, lru) {
                         if (count >= h->nr_huge_pages)
                                 return;
                         if (PageHighMem(page))
                                 continue;
                         list_del(&page->lru);
                         update_and_free_page(h, page);
                         h->free_huge_pages--;
                         h->free_huge_pages_node[page_to_nid(page)]--;
                 }
         }
 }
 #else
 static inline void try_to_free_low(struct hstate *h, unsigned long count,
                                                 nodemask_t *nodes_allowed)
 {
 }
 #endif
 
 /*
  * Increment or decrement surplus_huge_pages.  Keep node-specific counters
  * balanced by operating on them in a round-robin fashion.
  * Returns 1 if an adjustment was made.
  */
 static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
                                 int delta)
 {
         int start_nid, next_nid;
         int ret = 0;
 
         VM_BUG_ON(delta != -1 && delta != 1);
 
         if (delta < 0)
                 start_nid = hstate_next_node_to_alloc(h, nodes_allowed);
         else
                 start_nid = hstate_next_node_to_free(h, nodes_allowed);
         next_nid = start_nid;
 
         do {
                 int nid = next_nid;
                 if (delta < 0)  {
                         /*
                          * To shrink on this node, there must be a surplus page
                          */
                         if (!h->surplus_huge_pages_node[nid]) {
                                 next_nid = hstate_next_node_to_alloc(h,
                                                                 nodes_allowed);
                                 continue;
                         }
                 }
                 if (delta > 0) {
                         /*
                          * Surplus cannot exceed the total number of pages
                          */
                         if (h->surplus_huge_pages_node[nid] >=
                                                 h->nr_huge_pages_node[nid]) {
                                 next_nid = hstate_next_node_to_free(h,
                                                                 nodes_allowed);
                                 continue;
                         }
                 }
 
                 h->surplus_huge_pages += delta;
                 h->surplus_huge_pages_node[nid] += delta;
                 ret = 1;
                 break;
         } while (next_nid != start_nid);
 
         return ret;
 }
 
 #define persistent_huge_pages(h) (h->nr_huge_pages - h->surplus_huge_pages)
 static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
                                                 nodemask_t *nodes_allowed)
 {
         unsigned long min_count, ret;
 
         if (h->order >= MAX_ORDER)
                 return h->max_huge_pages;
 
         /*
          * Increase the pool size
          * First take pages out of surplus state.  Then make up the
          * remaining difference by allocating fresh huge pages.
          *
          * We might race with alloc_buddy_huge_page() here and be unable
          * to convert a surplus huge page to a normal huge page. That is
          * not critical, though, it just means the overall size of the
          * pool might be one hugepage larger than it needs to be, but
          * within all the constraints specified by the sysctls.
          */
         spin_lock(&hugetlb_lock);
         while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
                 if (!adjust_pool_surplus(h, nodes_allowed, -1))
                         break;
         }
 
         while (count > persistent_huge_pages(h)) {
                 /*
                  * If this allocation races such that we no longer need the
                  * page, free_huge_page will handle it by freeing the page
                  * and reducing the surplus.
                  */
                 spin_unlock(&hugetlb_lock);
                 ret = alloc_fresh_huge_page(h, nodes_allowed);
                 spin_lock(&hugetlb_lock);
                 if (!ret)
                         goto out;
 
                 /* Bail for signals. Probably ctrl-c from user */
                 if (signal_pending(current))
                         goto out;
         }
 
         /*
          * Decrease the pool size
          * First return free pages to the buddy allocator (being careful
          * to keep enough around to satisfy reservations).  Then place
          * pages into surplus state as needed so the pool will shrink
          * to the desired size as pages become free.
          *
          * By placing pages into the surplus state independent of the
          * overcommit value, we are allowing the surplus pool size to
          * exceed overcommit. There are few sane options here. Since
          * alloc_buddy_huge_page() is checking the global counter,
          * though, we'll note that we're not allowed to exceed surplus
          * and won't grow the pool anywhere else. Not until one of the
          * sysctls are changed, or the surplus pages go out of use.
          */
         min_count = h->resv_huge_pages + h->nr_huge_pages - h->free_huge_pages;
         min_count = max(count, min_count);
         try_to_free_low(h, min_count, nodes_allowed);
         while (min_count < persistent_huge_pages(h)) {
                 if (!free_pool_huge_page(h, nodes_allowed, 0))
                         break;
                 cond_resched_lock(&hugetlb_lock);
         }
         while (count < persistent_huge_pages(h)) {
                 if (!adjust_pool_surplus(h, nodes_allowed, 1))
                         break;
         }
 out:
         ret = persistent_huge_pages(h);
         spin_unlock(&hugetlb_lock);
         return ret;
 }
 
 #define HSTATE_ATTR_RO(_name) \
         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
 
 #define HSTATE_ATTR(_name) \
         static struct kobj_attribute _name##_attr = \
                 __ATTR(_name, 0644, _name##_show, _name##_store)
 
 static struct kobject *hugepages_kobj;
 static struct kobject *hstate_kobjs[HUGE_MAX_HSTATE];
 
 static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp);
 
 static struct hstate *kobj_to_hstate(struct kobject *kobj, int *nidp)
 {
         int i;
 
         for (i = 0; i < HUGE_MAX_HSTATE; i++)
                 if (hstate_kobjs[i] == kobj) {
                         if (nidp)
                                 *nidp = NUMA_NO_NODE;
                         return &hstates[i];
                 }
 
         return kobj_to_node_hstate(kobj, nidp);
 }
 
 static ssize_t nr_hugepages_show_common(struct kobject *kobj,
                                         struct kobj_attribute *attr, char *buf)
 {
         struct hstate *h;
         unsigned long nr_huge_pages;
         int nid;
 
         h = kobj_to_hstate(kobj, &nid);
         if (nid == NUMA_NO_NODE)
                 nr_huge_pages = h->nr_huge_pages;
         else
                 nr_huge_pages = h->nr_huge_pages_node[nid];
 
         return sprintf(buf, "%lu\n", nr_huge_pages);
 }
 
 static ssize_t nr_hugepages_store_common(bool obey_mempolicy,
                         struct kobject *kobj, struct kobj_attribute *attr,
                         const char *buf, size_t len)
 {
         int err;
         int nid;
         unsigned long count;
         struct hstate *h;
         NODEMASK_ALLOC(nodemask_t, nodes_allowed, GFP_KERNEL | __GFP_NORETRY);
 
         err = strict_strtoul(buf, 10, &count);
         if (err)
                 goto out;
 
         h = kobj_to_hstate(kobj, &nid);
         if (h->order >= MAX_ORDER) {
                 err = -EINVAL;
                 goto out;
         }
 
         if (nid == NUMA_NO_NODE) {
                 /*
                  * global hstate attribute
                  */
                 if (!(obey_mempolicy &&
                                 init_nodemask_of_mempolicy(nodes_allowed))) {
                         NODEMASK_FREE(nodes_allowed);
                         nodes_allowed = &node_states[N_MEMORY];
                 }
         } else if (nodes_allowed) {
                 /*
                  * per node hstate attribute: adjust count to global,
                  * but restrict alloc/free to the specified node.
                  */
                 count += h->nr_huge_pages - h->nr_huge_pages_node[nid];
                 init_nodemask_of_node(nodes_allowed, nid);
         } else
                 nodes_allowed = &node_states[N_MEMORY];
 
         h->max_huge_pages = set_max_huge_pages(h, count, nodes_allowed);
 
         if (nodes_allowed != &node_states[N_MEMORY])
                 NODEMASK_FREE(nodes_allowed);
 
         return len;
 out:
         NODEMASK_FREE(nodes_allowed);
         return err;
 }
 
 static ssize_t nr_hugepages_show(struct kobject *kobj,
                                        struct kobj_attribute *attr, char *buf)
 {
         return nr_hugepages_show_common(kobj, attr, buf);
 }
 
 static ssize_t nr_hugepages_store(struct kobject *kobj,
                struct kobj_attribute *attr, const char *buf, size_t len)
 {
         return nr_hugepages_store_common(false, kobj, attr, buf, len);
 }
 HSTATE_ATTR(nr_hugepages);
 
 #ifdef CONFIG_NUMA
 
 /*
  * hstate attribute for optionally mempolicy-based constraint on persistent
  * huge page alloc/free.
  */
 static ssize_t nr_hugepages_mempolicy_show(struct kobject *kobj,
                                        struct kobj_attribute *attr, char *buf)
 {
         return nr_hugepages_show_common(kobj, attr, buf);
 }
 
 static ssize_t nr_hugepages_mempolicy_store(struct kobject *kobj,
                struct kobj_attribute *attr, const char *buf, size_t len)
 {
         return nr_hugepages_store_common(true, kobj, attr, buf, len);
 }
 HSTATE_ATTR(nr_hugepages_mempolicy);
 #endif
 
 
 static ssize_t nr_overcommit_hugepages_show(struct kobject *kobj,
                                         struct kobj_attribute *attr, char *buf)
 {
         struct hstate *h = kobj_to_hstate(kobj, NULL);
         return sprintf(buf, "%lu\n", h->nr_overcommit_huge_pages);
 }
 
 static ssize_t nr_overcommit_hugepages_store(struct kobject *kobj,
                 struct kobj_attribute *attr, const char *buf, size_t count)
 {
         int err;
         unsigned long input;
         struct hstate *h = kobj_to_hstate(kobj, NULL);
 
         if (h->order >= MAX_ORDER)
                 return -EINVAL;
 
         err = strict_strtoul(buf, 10, &input);
         if (err)
                 return err;
 
         spin_lock(&hugetlb_lock);
         h->nr_overcommit_huge_pages = input;
         spin_unlock(&hugetlb_lock);
 
         return count;
 }
 HSTATE_ATTR(nr_overcommit_hugepages);
 
 static ssize_t free_hugepages_show(struct kobject *kobj,
                                         struct kobj_attribute *attr, char *buf)
 {
         struct hstate *h;
         unsigned long free_huge_pages;
         int nid;
 
         h = kobj_to_hstate(kobj, &nid);
         if (nid == NUMA_NO_NODE)
                 free_huge_pages = h->free_huge_pages;
         else
                 free_huge_pages = h->free_huge_pages_node[nid];
 
         return sprintf(buf, "%lu\n", free_huge_pages);
 }
 HSTATE_ATTR_RO(free_hugepages);
 
 static ssize_t resv_hugepages_show(struct kobject *kobj,
                                         struct kobj_attribute *attr, char *buf)
 {
         struct hstate *h = kobj_to_hstate(kobj, NULL);
         return sprintf(buf, "%lu\n", h->resv_huge_pages);
 }
 HSTATE_ATTR_RO(resv_hugepages);
 
 static ssize_t surplus_hugepages_show(struct kobject *kobj,
                                         struct kobj_attribute *attr, char *buf)
 {
         struct hstate *h;
         unsigned long surplus_huge_pages;
         int nid;
 
         h = kobj_to_hstate(kobj, &nid);
         if (nid == NUMA_NO_NODE)
                 surplus_huge_pages = h->surplus_huge_pages;
         else
                 surplus_huge_pages = h->surplus_huge_pages_node[nid];
 
         return sprintf(buf, "%lu\n", surplus_huge_pages);
 }
 HSTATE_ATTR_RO(surplus_hugepages);
 
 static struct attribute *hstate_attrs[] = {
         &nr_hugepages_attr.attr,
         &nr_overcommit_hugepages_attr.attr,
         &free_hugepages_attr.attr,
         &resv_hugepages_attr.attr,
         &surplus_hugepages_attr.attr,
 #ifdef CONFIG_NUMA
         &nr_hugepages_mempolicy_attr.attr,
 #endif
         NULL,
 };
 
 static struct attribute_group hstate_attr_group = {
         .attrs = hstate_attrs,
 };
 
 static int hugetlb_sysfs_add_hstate(struct hstate *h, struct kobject *parent,
                                     struct kobject **hstate_kobjs,
                                     struct attribute_group *hstate_attr_group)
 {
         int retval;
         int hi = hstate_index(h);
 
         hstate_kobjs[hi] = kobject_create_and_add(h->name, parent);
         if (!hstate_kobjs[hi])
                 return -ENOMEM;
 
         retval = sysfs_create_group(hstate_kobjs[hi], hstate_attr_group);
         if (retval)
                 kobject_put(hstate_kobjs[hi]);
 
         return retval;
 }
 
 static void __init hugetlb_sysfs_init(void)
 {
         struct hstate *h;
         int err;
 
         hugepages_kobj = kobject_create_and_add("hugepages", mm_kobj);
         if (!hugepages_kobj)
                 return;
 
         for_each_hstate(h) {
                 err = hugetlb_sysfs_add_hstate(h, hugepages_kobj,
                                          hstate_kobjs, &hstate_attr_group);
                 if (err)
                         pr_err("Hugetlb: Unable to add hstate %s", h->name);
         }
 }
 
 #ifdef CONFIG_NUMA
 
 /*
  * node_hstate/s - associate per node hstate attributes, via their kobjects,
  * with node devices in node_devices[] using a parallel array.  The array
  * index of a node device or _hstate == node id.
  * This is here to avoid any static dependency of the node device driver, in
  * the base kernel, on the hugetlb module.
  */
 struct node_hstate {
         struct kobject          *hugepages_kobj;
         struct kobject          *hstate_kobjs[HUGE_MAX_HSTATE];
 };
 struct node_hstate node_hstates[MAX_NUMNODES];
 
 /*
  * A subset of global hstate attributes for node devices
  */
 static struct attribute *per_node_hstate_attrs[] = {
         &nr_hugepages_attr.attr,
         &free_hugepages_attr.attr,
         &surplus_hugepages_attr.attr,
         NULL,
 };
 
 static struct attribute_group per_node_hstate_attr_group = {
         .attrs = per_node_hstate_attrs,
 };
 
 /*
  * kobj_to_node_hstate - lookup global hstate for node device hstate attr kobj.
  * Returns node id via non-NULL nidp.
  */
 static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp)
 {
         int nid;
 
         for (nid = 0; nid < nr_node_ids; nid++) {
                 struct node_hstate *nhs = &node_hstates[nid];
                 int i;
                 for (i = 0; i < HUGE_MAX_HSTATE; i++)
                         if (nhs->hstate_kobjs[i] == kobj) {
                                 if (nidp)
                                         *nidp = nid;
                                 return &hstates[i];
                         }
         }
 
         BUG();
         return NULL;
 }
 
 /*
  * Unregister hstate attributes from a single node device.
  * No-op if no hstate attributes attached.
  */
 static void hugetlb_unregister_node(struct node *node)
 {
         struct hstate *h;
         struct node_hstate *nhs = &node_hstates[node->dev.id];
 
         if (!nhs->hugepages_kobj)
                 return;         /* no hstate attributes */
 
         for_each_hstate(h) {
                 int idx = hstate_index(h);
                 if (nhs->hstate_kobjs[idx]) {
                         kobject_put(nhs->hstate_kobjs[idx]);
                         nhs->hstate_kobjs[idx] = NULL;
                 }
         }
 
         kobject_put(nhs->hugepages_kobj);
         nhs->hugepages_kobj = NULL;
 }
 
 /*
  * hugetlb module exit:  unregister hstate attributes from node devices
  * that have them.
  */
 static void hugetlb_unregister_all_nodes(void)
 {
         int nid;
 
         /*
          * disable node device registrations.
          */
         register_hugetlbfs_with_node(NULL, NULL);
 
         /*
          * remove hstate attributes from any nodes that have them.
          */
         for (nid = 0; nid < nr_node_ids; nid++)
                 hugetlb_unregister_node(node_devices[nid]);
 }
 
 /*
  * Register hstate attributes for a single node device.
  * No-op if attributes already registered.
  */
 static void hugetlb_register_node(struct node *node)
 {
         struct hstate *h;
         struct node_hstate *nhs = &node_hstates[node->dev.id];
         int err;
 
         if (nhs->hugepages_kobj)
                 return;         /* already allocated */
 
         nhs->hugepages_kobj = kobject_create_and_add("hugepages",
                                                         &node->dev.kobj);
         if (!nhs->hugepages_kobj)
                 return;
 
         for_each_hstate(h) {
                 err = hugetlb_sysfs_add_hstate(h, nhs->hugepages_kobj,
                                                 nhs->hstate_kobjs,
                                                 &per_node_hstate_attr_group);
                 if (err) {
                         pr_err("Hugetlb: Unable to add hstate %s for node %d\n",
                                 h->name, node->dev.id);
                         hugetlb_unregister_node(node);
                         break;
                 }
         }
 }
 
 /*
  * hugetlb init time:  register hstate attributes for all registered node
  * devices of nodes that have memory.  All on-line nodes should have
  * registered their associated device by this time.
  */
 static void hugetlb_register_all_nodes(void)
 {
         int nid;
 
         for_each_node_state(nid, N_MEMORY) {
                 struct node *node = node_devices[nid];
                 if (node->dev.id == nid)
                         hugetlb_register_node(node);
         }
 
         /*
          * Let the node device driver know we're here so it can
          * [un]register hstate attributes on node hotplug.
          */
         register_hugetlbfs_with_node(hugetlb_register_node,
                                      hugetlb_unregister_node);
 }
 #else   /* !CONFIG_NUMA */
 
 static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp)
 {
         BUG();
         if (nidp)
                 *nidp = -1;
         return NULL;
 }
 
 static void hugetlb_unregister_all_nodes(void) { }
 
 static void hugetlb_register_all_nodes(void) { }
 
 #endif
 
 static void __exit hugetlb_exit(void)
 {
         struct hstate *h;
 
         hugetlb_unregister_all_nodes();
 
         for_each_hstate(h) {
                 kobject_put(hstate_kobjs[hstate_index(h)]);
         }
 
         kobject_put(hugepages_kobj);
 }
 module_exit(hugetlb_exit);
 
 static int __init hugetlb_init(void)
 {
         /* Some platform decide whether they support huge pages at boot
          * time. On these, such as powerpc, HPAGE_SHIFT is set to 0 when
          * there is no such support
          */
         if (HPAGE_SHIFT == 0)
                 return 0;
 
         if (!size_to_hstate(default_hstate_size)) {
                 default_hstate_size = HPAGE_SIZE;
                 if (!size_to_hstate(default_hstate_size))
                         hugetlb_add_hstate(HUGETLB_PAGE_ORDER);
         }
         default_hstate_idx = hstate_index(size_to_hstate(default_hstate_size));
         if (default_hstate_max_huge_pages)
                 default_hstate.max_huge_pages = default_hstate_max_huge_pages;
 
         hugetlb_init_hstates();
         gather_bootmem_prealloc();
         report_hugepages();
 
         hugetlb_sysfs_init();
         hugetlb_register_all_nodes();
         hugetlb_cgroup_file_init();
 
         return 0;
 }
 module_init(hugetlb_init);
 
 /* Should be called on processing a hugepagesz=... option */
 void __init hugetlb_add_hstate(unsigned order)
 {
         struct hstate *h;
         unsigned long i;
 
         if (size_to_hstate(PAGE_SIZE << order)) {
                 pr_warning("hugepagesz= specified twice, ignoring\n");
                 return;
         }
         BUG_ON(hugetlb_max_hstate >= HUGE_MAX_HSTATE);
         BUG_ON(order == 0);
         h = &hstates[hugetlb_max_hstate++];
         h->order = order;
         h->mask = ~((1ULL << (order + PAGE_SHIFT)) - 1);
         h->nr_huge_pages = 0;
         h->free_huge_pages = 0;
         for (i = 0; i < MAX_NUMNODES; ++i)
                 INIT_LIST_HEAD(&h->hugepage_freelists[i]);
         INIT_LIST_HEAD(&h->hugepage_activelist);
         h->next_nid_to_alloc = first_node(node_states[N_MEMORY]);
         h->next_nid_to_free = first_node(node_states[N_MEMORY]);
         snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
                                         huge_page_size(h)/1024);
 
         parsed_hstate = h;
 }
 
 static int __init hugetlb_nrpages_setup(char *s)
 {
         unsigned long *mhp;
         static unsigned long *last_mhp;
 
         /*
          * !hugetlb_max_hstate means we haven't parsed a hugepagesz= parameter yet,
          * so this hugepages= parameter goes to the "default hstate".
          */
         if (!hugetlb_max_hstate)
                 mhp = &default_hstate_max_huge_pages;
         else
                 mhp = &parsed_hstate->max_huge_pages;
 
         if (mhp == last_mhp) {
                 pr_warning("hugepages= specified twice without "
                            "interleaving hugepagesz=, ignoring\n");
                 return 1;
         }
 
         if (sscanf(s, "%lu", mhp) <= 0)
                 *mhp = 0;
 
         /*
          * Global state is always initialized later in hugetlb_init.
          * But we need to allocate >= MAX_ORDER hstates here early to still
          * use the bootmem allocator.
          */
         if (hugetlb_max_hstate && parsed_hstate->order >= MAX_ORDER)
                 hugetlb_hstate_alloc_pages(parsed_hstate);
 
         last_mhp = mhp;
 
         return 1;
 }
 __setup("hugepages=", hugetlb_nrpages_setup);
 
 static int __init hugetlb_default_setup(char *s)
 {
         default_hstate_size = memparse(s, &s);
         return 1;
 }
 __setup("default_hugepagesz=", hugetlb_default_setup);
 
 static unsigned int cpuset_mems_nr(unsigned int *array)
 {
         int node;
         unsigned int nr = 0;
 
         for_each_node_mask(node, cpuset_current_mems_allowed)
                 nr += array[node];
 
         return nr;
 }
 
 #ifdef CONFIG_SYSCTL
 static int hugetlb_sysctl_handler_common(bool obey_mempolicy,
                          struct ctl_table *table, int write,
                          void __user *buffer, size_t *length, loff_t *ppos)
 {
         struct hstate *h = &default_hstate;
         unsigned long tmp;
         int ret;
 
         tmp = h->max_huge_pages;
 
         if (write && h->order >= MAX_ORDER)
                 return -EINVAL;
 
         table->data = &tmp;
         table->maxlen = sizeof(unsigned long);
         ret = proc_doulongvec_minmax(table, write, buffer, length, ppos);
         if (ret)
                 goto out;
 
         if (write) {
                 NODEMASK_ALLOC(nodemask_t, nodes_allowed,
                                                 GFP_KERNEL | __GFP_NORETRY);
                 if (!(obey_mempolicy &&
                                init_nodemask_of_mempolicy(nodes_allowed))) {
                         NODEMASK_FREE(nodes_allowed);
                         nodes_allowed = &node_states[N_MEMORY];
                 }
                 h->max_huge_pages = set_max_huge_pages(h, tmp, nodes_allowed);
 
                 if (nodes_allowed != &node_states[N_MEMORY])
                         NODEMASK_FREE(nodes_allowed);
         }
 out:
         return ret;
 }
 
 int hugetlb_sysctl_handler(struct ctl_table *table, int write,
                           void __user *buffer, size_t *length, loff_t *ppos)
 {
 
         return hugetlb_sysctl_handler_common(false, table, write,
                                                         buffer, length, ppos);
 }
 
 #ifdef CONFIG_NUMA
 int hugetlb_mempolicy_sysctl_handler(struct ctl_table *table, int write,
                           void __user *buffer, size_t *length, loff_t *ppos)
 {
         return hugetlb_sysctl_handler_common(true, table, write,
                                                         buffer, length, ppos);
 }
 #endif /* CONFIG_NUMA */
 
 int hugetlb_treat_movable_handler(struct ctl_table *table, int write,
                         void __user *buffer,
                         size_t *length, loff_t *ppos)
 {
         proc_dointvec(table, write, buffer, length, ppos);
         if (hugepages_treat_as_movable)
                 htlb_alloc_mask = GFP_HIGHUSER_MOVABLE;
         else
                 htlb_alloc_mask = GFP_HIGHUSER;
         return 0;
 }
 
 int hugetlb_overcommit_handler(struct ctl_table *table, int write,
                         void __user *buffer,
                         size_t *length, loff_t *ppos)
 {
         struct hstate *h = &default_hstate;
         unsigned long tmp;
         int ret;
 
         tmp = h->nr_overcommit_huge_pages;
 
         if (write && h->order >= MAX_ORDER)
                 return -EINVAL;
 
         table->data = &tmp;
         table->maxlen = sizeof(unsigned long);
         ret = proc_doulongvec_minmax(table, write, buffer, length, ppos);
         if (ret)
                 goto out;
 
         if (write) {
                 spin_lock(&hugetlb_lock);
                 h->nr_overcommit_huge_pages = tmp;
                 spin_unlock(&hugetlb_lock);
         }
 out:
         return ret;
 }
 
 #endif /* CONFIG_SYSCTL */
 
 void hugetlb_report_meminfo(struct seq_file *m)
 {
         struct hstate *h = &default_hstate;
         seq_printf(m,
                         "HugePages_Total:   %5lu\n"
                         "HugePages_Free:    %5lu\n"
                         "HugePages_Rsvd:    %5lu\n"
                         "HugePages_Surp:    %5lu\n"
                         "Hugepagesize:   %8lu kB\n",
                         h->nr_huge_pages,
                         h->free_huge_pages,
                         h->resv_huge_pages,
                         h->surplus_huge_pages,
                         1UL << (huge_page_order(h) + PAGE_SHIFT - 10));
 }
 
 int hugetlb_report_node_meminfo(int nid, char *buf)
 {
         struct hstate *h = &default_hstate;
         return sprintf(buf,
                 "Node %d HugePages_Total: %5u\n"
                 "Node %d HugePages_Free:  %5u\n"
                 "Node %d HugePages_Surp:  %5u\n",
                 nid, h->nr_huge_pages_node[nid],
                 nid, h->free_huge_pages_node[nid],
                 nid, h->surplus_huge_pages_node[nid]);
 }
 
 void hugetlb_show_meminfo(void)
 {
         struct hstate *h;
         int nid;
 
         for_each_node_state(nid, N_MEMORY)
                 for_each_hstate(h)
                         pr_info("Node %d hugepages_total=%u hugepages_free=%u hugepages_surp=%u hugepages_size=%lukB\n",
                                 nid,
                                 h->nr_huge_pages_node[nid],
                                 h->free_huge_pages_node[nid],
                                 h->surplus_huge_pages_node[nid],
                                 1UL << (huge_page_order(h) + PAGE_SHIFT - 10));
 }
 
 /* Return the number pages of memory we physically have, in PAGE_SIZE units. */
 unsigned long hugetlb_total_pages(void)
 {
         struct hstate *h;
         unsigned long nr_total_pages = 0;
 
         for_each_hstate(h)
                 nr_total_pages += h->nr_huge_pages * pages_per_huge_page(h);
         return nr_total_pages;
 }
 
 static int hugetlb_acct_memory(struct hstate *h, long delta)
 {
         int ret = -ENOMEM;
 
         spin_lock(&hugetlb_lock);
         /*
          * When cpuset is configured, it breaks the strict hugetlb page
          * reservation as the accounting is done on a global variable. Such
          * reservation is completely rubbish in the presence of cpuset because
          * the reservation is not checked against page availability for the
          * current cpuset. Application can still potentially OOM'ed by kernel
          * with lack of free htlb page in cpuset that the task is in.
          * Attempt to enforce strict accounting with cpuset is almost
          * impossible (or too ugly) because cpuset is too fluid that
          * task or memory node can be dynamically moved between cpusets.
          *
          * The change of semantics for shared hugetlb mapping with cpuset is
          * undesirable. However, in order to preserve some of the semantics,
          * we fall back to check against current free page availability as
          * a best attempt and hopefully to minimize the impact of changing
          * semantics that cpuset has.
          */
         if (delta > 0) {
                 if (gather_surplus_pages(h, delta) < 0)
                         goto out;
 
                 if (delta > cpuset_mems_nr(h->free_huge_pages_node)) {
                         return_unused_surplus_pages(h, delta);
                         goto out;
                 }
         }
 
         ret = 0;
         if (delta < 0)
                 return_unused_surplus_pages(h, (unsigned long) -delta);
 
 out:
         spin_unlock(&hugetlb_lock);
         return ret;
 }
 
 static void hugetlb_vm_op_open(struct vm_area_struct *vma)
 {
         struct resv_map *reservations = vma_resv_map(vma);
 
         /*
          * This new VMA should share its siblings reservation map if present.
          * The VMA will only ever have a valid reservation map pointer where
          * it is being copied for another still existing VMA.  As that VMA
          * has a reference to the reservation map it cannot disappear until
          * after this open call completes.  It is therefore safe to take a
          * new reference here without additional locking.
          */
         if (reservations)
                 kref_get(&reservations->refs);
 }
 
 static void resv_map_put(struct vm_area_struct *vma)
 {
         struct resv_map *reservations = vma_resv_map(vma);
 
         if (!reservations)
                 return;
         kref_put(&reservations->refs, resv_map_release);
 }
 
 static void hugetlb_vm_op_close(struct vm_area_struct *vma)
 {
         struct hstate *h = hstate_vma(vma);
         struct resv_map *reservations = vma_resv_map(vma);
         struct hugepage_subpool *spool = subpool_vma(vma);
         unsigned long reserve;
         unsigned long start;
         unsigned long end;
 
         if (reservations) {
                 start = vma_hugecache_offset(h, vma, vma->vm_start);
                 end = vma_hugecache_offset(h, vma, vma->vm_end);
 
                 reserve = (end - start) -
                         region_count(&reservations->regions, start, end);
 
                 resv_map_put(vma);
 
                 if (reserve) {
                         hugetlb_acct_memory(h, -reserve);
                         hugepage_subpool_put_pages(spool, reserve);
                 }
         }
 }
 
 /*
  * We cannot handle pagefaults against hugetlb pages at all.  They cause
  * handle_mm_fault() to try to instantiate regular-sized pages in the
  * hugegpage VMA.  do_page_fault() is supposed to trap this, so BUG is we get
  * this far.
  */
 static int hugetlb_vm_op_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
         BUG();
         return 0;
 }
 
 const struct vm_operations_struct hugetlb_vm_ops = {
         .fault = hugetlb_vm_op_fault,
         .open = hugetlb_vm_op_open,
         .close = hugetlb_vm_op_close,
 };
 
 static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,
                                 int writable)
 {
         pte_t entry;
 
         if (writable) {
                 entry = huge_pte_mkwrite(huge_pte_mkdirty(mk_huge_pte(page,
                                          vma->vm_page_prot)));
         } else {
                 entry = huge_pte_wrprotect(mk_huge_pte(page,
                                            vma->vm_page_prot));
         }
         entry = pte_mkyoung(entry);
         entry = pte_mkhuge(entry);
         entry = arch_make_huge_pte(entry, vma, page, writable);
 
         return entry;
 }
 
 static void set_huge_ptep_writable(struct vm_area_struct *vma,
                                    unsigned long address, pte_t *ptep)
 {
         pte_t entry;
 
         entry = huge_pte_mkwrite(huge_pte_mkdirty(huge_ptep_get(ptep)));
         if (huge_ptep_set_access_flags(vma, address, ptep, entry, 1))
                 update_mmu_cache(vma, address, ptep);
 }
 
 static int is_hugetlb_entry_migration(pte_t pte)
 {
         swp_entry_t swp;
 
         if (huge_pte_none(pte) || pte_present(pte))
                 return 0;
         swp = pte_to_swp_entry(pte);
         if (non_swap_entry(swp) && is_migration_entry(swp))
                 return 1;
         else
                 return 0;
 }
 
 static int is_hugetlb_entry_hwpoisoned(pte_t pte)
 {
         swp_entry_t swp;
 
         if (huge_pte_none(pte) || pte_present(pte))
                 return 0;
         swp = pte_to_swp_entry(pte);
         if (non_swap_entry(swp) && is_hwpoison_entry(swp))
                 return 1;
         else
                 return 0;
 }
 
 int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
                             struct vm_area_struct *vma)
 {
         pte_t *src_pte, *dst_pte, entry;
         struct page *ptepage;
         unsigned long addr;
         int cow;
         struct hstate *h = hstate_vma(vma);
         unsigned long sz = huge_page_size(h);
 
         cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
 
         for (addr = vma->vm_start; addr < vma->vm_end; addr += sz) {
                 src_pte = huge_pte_offset(src, addr);
                 if (!src_pte)
                         continue;
                 dst_pte = huge_pte_alloc(dst, addr, sz);
                 if (!dst_pte)
                         goto nomem;
 
                 /* If the pagetables are shared don't copy or take references */
                 if (dst_pte == src_pte)
                         continue;
 
                 spin_lock(&dst->page_table_lock);
                 spin_lock_nested(&src->page_table_lock, SINGLE_DEPTH_NESTING);
                 entry = huge_ptep_get(src_pte);
                 if (huge_pte_none(entry)) { /* skip none entry */
                         ;
                 } else if (unlikely(is_hugetlb_entry_migration(entry) ||
                                     is_hugetlb_entry_hwpoisoned(entry))) {
                         swp_entry_t swp_entry = pte_to_swp_entry(entry);
 
                         if (is_write_migration_entry(swp_entry) && cow) {
                                 /*
                                  * COW mappings require pages in both
                                  * parent and child to be set to read.
                                  */
                                 make_migration_entry_read(&swp_entry);
                                 entry = swp_entry_to_pte(swp_entry);
                                 set_huge_pte_at(src, addr, src_pte, entry);
                         }
                         set_huge_pte_at(dst, addr, dst_pte, entry);
                 } else {
                         if (cow)
                                 huge_ptep_set_wrprotect(src, addr, src_pte);
                         entry = huge_ptep_get(src_pte);
                         ptepage = pte_page(entry);
                         get_page(ptepage);
                         page_dup_rmap(ptepage);
                         set_huge_pte_at(dst, addr, dst_pte, entry);
                 }
                 spin_unlock(&src->page_table_lock);
                 spin_unlock(&dst->page_table_lock);
         }
         return 0;
 
 nomem:
         return -ENOMEM;
 }
 
 void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
                             unsigned long start, unsigned long end,
                             struct page *ref_page)
 {
         int force_flush = 0;
         struct mm_struct *mm = vma->vm_mm;
         unsigned long address;
         pte_t *ptep;
         pte_t pte;
         struct page *page;
         struct hstate *h = hstate_vma(vma);
         unsigned long sz = huge_page_size(h);
         const unsigned long mmun_start = start; /* For mmu_notifiers */
         const unsigned long mmun_end   = end;   /* For mmu_notifiers */
 
         WARN_ON(!is_vm_hugetlb_page(vma));
         BUG_ON(start & ~huge_page_mask(h));
         BUG_ON(end & ~huge_page_mask(h));
 
         tlb_start_vma(tlb, vma);
         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 again:
         spin_lock(&mm->page_table_lock);
         for (address = start; address < end; address += sz) {
                 ptep = huge_pte_offset(mm, address);
                 if (!ptep)
                         continue;
 
                 if (huge_pmd_unshare(mm, &address, ptep))
                         continue;
 
                 pte = huge_ptep_get(ptep);
                 if (huge_pte_none(pte))
                         continue;
 
                 /*
                  * Migrating hugepage or HWPoisoned hugepage is already
                  * unmapped and its refcount is dropped, so just clear pte here.
                  */
                 if (unlikely(!pte_present(pte))) {
                         huge_pte_clear(mm, address, ptep);
                         continue;
                 }
 
                 page = pte_page(pte);
                 /*
                  * If a reference page is supplied, it is because a specific
                  * page is being unmapped, not a range. Ensure the page we
                  * are about to unmap is the actual page of interest.
                  */
                 if (ref_page) {
                         if (page != ref_page)
                                 continue;
 
                         /*
                          * Mark the VMA as having unmapped its page so that
                          * future faults in this VMA will fail rather than
                          * looking like data was lost
                          */
                         set_vma_resv_flags(vma, HPAGE_RESV_UNMAPPED);
                 }
 
                 pte = huge_ptep_get_and_clear(mm, address, ptep);
                 tlb_remove_tlb_entry(tlb, ptep, address);
                 if (huge_pte_dirty(pte))
                         set_page_dirty(page);
 
                 page_remove_rmap(page);
                 force_flush = !__tlb_remove_page(tlb, page);
                 if (force_flush)
                         break;
                 /* Bail out after unmapping reference page if supplied */
                 if (ref_page)
                         break;
         }
         spin_unlock(&mm->page_table_lock);
         /*
          * mmu_gather ran out of room to batch pages, we break out of
          * the PTE lock to avoid doing the potential expensive TLB invalidate
          * and page-free while holding it.
          */
         if (force_flush) {
                 force_flush = 0;
                 tlb_flush_mmu(tlb);
                 if (address < end && !ref_page)
                         goto again;
         }
         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
         tlb_end_vma(tlb, vma);
 }
 
 void __unmap_hugepage_range_final(struct mmu_gather *tlb,
                           struct vm_area_struct *vma, unsigned long start,
                           unsigned long end, struct page *ref_page)
 {
         __unmap_hugepage_range(tlb, vma, start, end, ref_page);
 
         /*
          * Clear this flag so that x86's huge_pmd_share page_table_shareable
          * test will fail on a vma being torn down, and not grab a page table
          * on its way out.  We're lucky that the flag has such an appropriate
          * name, and can in fact be safely cleared here. We could clear it
          * before the __unmap_hugepage_range above, but all that's necessary
          * is to clear it before releasing the i_mmap_mutex. This works
          * because in the context this is called, the VMA is about to be
          * destroyed and the i_mmap_mutex is held.
          */
         vma->vm_flags &= ~VM_MAYSHARE;
 }
 
 void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
                           unsigned long end, struct page *ref_page)
 {
         struct mm_struct *mm;
         struct mmu_gather tlb;
 
         mm = vma->vm_mm;
 
         tlb_gather_mmu(&tlb, mm, start, end);
         __unmap_hugepage_range(&tlb, vma, start, end, ref_page);
         tlb_finish_mmu(&tlb, start, end);
 }
 
 /*
  * This is called when the original mapper is failing to COW a MAP_PRIVATE
  * mappping it owns the reserve page for. The intention is to unmap the page
  * from other VMAs and let the children be SIGKILLed if they are faulting the
  * same region.
  */
 static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
                                 struct page *page, unsigned long address)
 {
         struct hstate *h = hstate_vma(vma);
         struct vm_area_struct *iter_vma;
         struct address_space *mapping;
         pgoff_t pgoff;
 
         /*
          * vm_pgoff is in PAGE_SIZE units, hence the different calculation
          * from page cache lookup which is in HPAGE_SIZE units.
          */
         address = address & huge_page_mask(h);
         pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) +
                         vma->vm_pgoff;
         mapping = file_inode(vma->vm_file)->i_mapping;
 
         /*
          * Take the mapping lock for the duration of the table walk. As
          * this mapping should be shared between all the VMAs,
          * __unmap_hugepage_range() is called as the lock is already held
          */
         mutex_lock(&mapping->i_mmap_mutex);
         vma_interval_tree_foreach(iter_vma, &mapping->i_mmap, pgoff, pgoff) {
                 /* Do not unmap the current VMA */
                 if (iter_vma == vma)
                         continue;
 
                 /*
                  * Shared VMAs have their own reserves and do not affect
                  * MAP_PRIVATE accounting but it is possible that a shared
                  * VMA is using the same page so check and skip such VMAs.
                  */
                 if (iter_vma->vm_flags & VM_MAYSHARE)
                         continue;
 
                 /*
                  * Unmap the page from other VMAs without their own reserves.
                  * They get marked to be SIGKILLed if they fault in these
                  * areas. This is because a future no-page fault on this VMA
                  * could insert a zeroed page instead of the data existing
                  * from the time of fork. This would look like data corruption
                  */
                 if (!is_vma_resv_set(iter_vma, HPAGE_RESV_OWNER))
                         unmap_hugepage_range(iter_vma, address,
                                              address + huge_page_size(h), page);
         }
         mutex_unlock(&mapping->i_mmap_mutex);
 
         return 1;
 }
 
 /*
  * Hugetlb_cow() should be called with page lock of the original hugepage held.
  * Called with hugetlb_instantiation_mutex held and pte_page locked so we
  * cannot race with other handlers or page migration.
  * Keep the pte_same checks anyway to make transition from the mutex easier.
  */
 static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
                         unsigned long address, pte_t *ptep, pte_t pte,
                         struct page *pagecache_page)
 {
         struct hstate *h = hstate_vma(vma);
         struct page *old_page, *new_page;
         int avoidcopy;
         int outside_reserve = 0;
         unsigned long mmun_start;       /* For mmu_notifiers */
         unsigned long mmun_end;         /* For mmu_notifiers */
 
         old_page = pte_page(pte);
 
 retry_avoidcopy:
         /* If no-one else is actually using this page, avoid the copy
          * and just make the page writable */
         avoidcopy = (page_mapcount(old_page) == 1);
         if (avoidcopy) {
                 if (PageAnon(old_page))
                         page_move_anon_rmap(old_page, vma, address);
                 set_huge_ptep_writable(vma, address, ptep);
                 return 0;
         }
 
         /*
          * If the process that created a MAP_PRIVATE mapping is about to
          * perform a COW due to a shared page count, attempt to satisfy
          * the allocation without using the existing reserves. The pagecache
          * page is used to determine if the reserve at this address was
          * consumed or not. If reserves were used, a partial faulted mapping
          * at the time of fork() could consume its reserves on COW instead
          * of the full address range.
          */
         if (!(vma->vm_flags & VM_MAYSHARE) &&
                         is_vma_resv_set(vma, HPAGE_RESV_OWNER) &&
                         old_page != pagecache_page)
                 outside_reserve = 1;
 
         page_cache_get(old_page);
 
         /* Drop page_table_lock as buddy allocator may be called */
         spin_unlock(&mm->page_table_lock);
         new_page = alloc_huge_page(vma, address, outside_reserve);
 
         if (IS_ERR(new_page)) {
                 long err = PTR_ERR(new_page);
                 page_cache_release(old_page);
 
                 /*
                  * If a process owning a MAP_PRIVATE mapping fails to COW,
                  * it is due to references held by a child and an insufficient
                  * huge page pool. To guarantee the original mappers
                  * reliability, unmap the page from child processes. The child
                  * may get SIGKILLed if it later faults.
                  */
                 if (outside_reserve) {
                         BUG_ON(huge_pte_none(pte));
                         if (unmap_ref_private(mm, vma, old_page, address)) {
                                 BUG_ON(huge_pte_none(pte));
                                 spin_lock(&mm->page_table_lock);
                                 ptep = huge_pte_offset(mm, address & huge_page_mask(h));
                                 if (likely(pte_same(huge_ptep_get(ptep), pte)))
                                         goto retry_avoidcopy;
                                 /*
                                  * race occurs while re-acquiring page_table_lock, and
                                  * our job is done.
                                  */
                                 return 0;
                         }
                         WARN_ON_ONCE(1);
                 }
 
                 /* Caller expects lock to be held */
                 spin_lock(&mm->page_table_lock);
                 if (err == -ENOMEM)
                         return VM_FAULT_OOM;
                 else
                         return VM_FAULT_SIGBUS;
         }
 
         /*
          * When the original hugepage is shared one, it does not have
          * anon_vma prepared.
          */
         if (unlikely(anon_vma_prepare(vma))) {
                 page_cache_release(new_page);
                 page_cache_release(old_page);
                 /* Caller expects lock to be held */
                 spin_lock(&mm->page_table_lock);
                 return VM_FAULT_OOM;
         }
 
         copy_user_huge_page(new_page, old_page, address, vma,
                             pages_per_huge_page(h));
         __SetPageUptodate(new_page);
 
         mmun_start = address & huge_page_mask(h);
         mmun_end = mmun_start + huge_page_size(h);
         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
         /*
          * Retake the page_table_lock to check for racing updates
          * before the page tables are altered
          */
         spin_lock(&mm->page_table_lock);
         ptep = huge_pte_offset(mm, address & huge_page_mask(h));
         if (likely(pte_same(huge_ptep_get(ptep), pte))) {
                 /* Break COW */
                 huge_ptep_clear_flush(vma, address, ptep);
                 set_huge_pte_at(mm, address, ptep,
                                 make_huge_pte(vma, new_page, 1));
                 page_remove_rmap(old_page);
                 hugepage_add_new_anon_rmap(new_page, vma, address);
                 /* Make the old page be freed below */
                 new_page = old_page;
         }
         spin_unlock(&mm->page_table_lock);
         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
         /* Caller expects lock to be held */
         spin_lock(&mm->page_table_lock);
         page_cache_release(new_page);
         page_cache_release(old_page);
         return 0;
 }
 
 /* Return the pagecache page at a given address within a VMA */
 static struct page *hugetlbfs_pagecache_page(struct hstate *h,
                         struct vm_area_struct *vma, unsigned long address)
 {
         struct address_space *mapping;
         pgoff_t idx;
 
         mapping = vma->vm_file->f_mapping;
         idx = vma_hugecache_offset(h, vma, address);
 
         return find_lock_page(mapping, idx);
 }
 
 /*
  * Return whether there is a pagecache page to back given address within VMA.
  * Caller follow_hugetlb_page() holds page_table_lock so we cannot lock_page.
  */
 static bool hugetlbfs_pagecache_present(struct hstate *h,
                         struct vm_area_struct *vma, unsigned long address)
 {
         struct address_space *mapping;
         pgoff_t idx;
         struct page *page;
 
         mapping = vma->vm_file->f_mapping;
         idx = vma_hugecache_offset(h, vma, address);
 
         page = find_get_page(mapping, idx);
         if (page)
                 put_page(page);
         return page != NULL;
 }
 
 static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
                         unsigned long address, pte_t *ptep, unsigned int flags)
 {
         struct hstate *h = hstate_vma(vma);
         int ret = VM_FAULT_SIGBUS;
         int anon_rmap = 0;
         pgoff_t idx;
         unsigned long size;
         struct page *page;
         struct address_space *mapping;
         pte_t new_pte;
 
         /*
          * Currently, we are forced to kill the process in the event the
          * original mapper has unmapped pages from the child due to a failed
          * COW. Warn that such a situation has occurred as it may not be obvious
          */
         if (is_vma_resv_set(vma, HPAGE_RESV_UNMAPPED)) {
                 pr_warning("PID %d killed due to inadequate hugepage pool\n",
                            current->pid);
                 return ret;
         }
 
         mapping = vma->vm_file->f_mapping;
         idx = vma_hugecache_offset(h, vma, address);
 
         /*
          * Use page lock to guard against racing truncation
          * before we get page_table_lock.
          */
 retry:
         page = find_lock_page(mapping, idx);
         if (!page) {
                 size = i_size_read(mapping->host) >> huge_page_shift(h);
                 if (idx >= size)
                         goto out;
                 page = alloc_huge_page(vma, address, 0);
                 if (IS_ERR(page)) {
                         ret = PTR_ERR(page);
                         if (ret == -ENOMEM)
                                 ret = VM_FAULT_OOM;
                         else
                                 ret = VM_FAULT_SIGBUS;
                         goto out;
                 }
                 clear_huge_page(page, address, pages_per_huge_page(h));
                 __SetPageUptodate(page);
 
                 if (vma->vm_flags & VM_MAYSHARE) {
                         int err;
                         struct inode *inode = mapping->host;
 
                         err = add_to_page_cache(page, mapping, idx, GFP_KERNEL);
                         if (err) {
                                 put_page(page);
                                 if (err == -EEXIST)
                                         goto retry;
                                 goto out;
                         }
 
                         spin_lock(&inode->i_lock);
                         inode->i_blocks += blocks_per_huge_page(h);
                         spin_unlock(&inode->i_lock);
                 } else {
                         lock_page(page);
                         if (unlikely(anon_vma_prepare(vma))) {
                                 ret = VM_FAULT_OOM;
                                 goto backout_unlocked;
                         }
                         anon_rmap = 1;
                 }
         } else {
                 /*
                  * If memory error occurs between mmap() and fault, some process
                  * don't have hwpoisoned swap entry for errored virtual address.
                  * So we need to block hugepage fault by PG_hwpoison bit check.
                  */
                 if (unlikely(PageHWPoison(page))) {
                         ret = VM_FAULT_HWPOISON |
                                 VM_FAULT_SET_HINDEX(hstate_index(h));
                         goto backout_unlocked;
                 }
         }
 
         /*
          * If we are going to COW a private mapping later, we examine the
          * pending reservations for this page now. This will ensure that
          * any allocations necessary to record that reservation occur outside
          * the spinlock.
          */
         if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED))
                 if (vma_needs_reservation(h, vma, address) < 0) {
                         ret = VM_FAULT_OOM;
                         goto backout_unlocked;
                 }
 
         spin_lock(&mm->page_table_lock);
         size = i_size_read(mapping->host) >> huge_page_shift(h);
         if (idx >= size)
                 goto backout;
 
         ret = 0;
         if (!huge_pte_none(huge_ptep_get(ptep)))
                 goto backout;
 
         if (anon_rmap)
                 hugepage_add_new_anon_rmap(page, vma, address);
         else
                 page_dup_rmap(page);
         new_pte = make_huge_pte(vma, page, ((vma->vm_flags & VM_WRITE)
                                 && (vma->vm_flags & VM_SHARED)));
         set_huge_pte_at(mm, address, ptep, new_pte);
 
         if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
                 /* Optimization, do the COW without a second fault */
                 ret = hugetlb_cow(mm, vma, address, ptep, new_pte, page);
         }
 
         spin_unlock(&mm->page_table_lock);
         unlock_page(page);
 out:
         return ret;
 
 backout:
         spin_unlock(&mm->page_table_lock);
 backout_unlocked:
         unlock_page(page);
         put_page(page);
         goto out;
 }
 
 int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                         unsigned long address, unsigned int flags)
 {
         pte_t *ptep;
         pte_t entry;
         int ret;
         struct page *page = NULL;
         struct page *pagecache_page = NULL;
         static DEFINE_MUTEX(hugetlb_instantiation_mutex);
         struct hstate *h = hstate_vma(vma);
 
         address &= huge_page_mask(h);
 
         ptep = huge_pte_offset(mm, address);
         if (ptep) {
                 entry = huge_ptep_get(ptep);
                 if (unlikely(is_hugetlb_entry_migration(entry))) {
                         migration_entry_wait_huge(mm, ptep);
                         return 0;
                 } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
                         return VM_FAULT_HWPOISON_LARGE |
                                 VM_FAULT_SET_HINDEX(hstate_index(h));
         }
 
         ptep = huge_pte_alloc(mm, address, huge_page_size(h));
         if (!ptep)
                 return VM_FAULT_OOM;
 
         /*
          * Serialize hugepage allocation and instantiation, so that we don't
          * get spurious allocation failures if two CPUs race to instantiate
          * the same page in the page cache.
          */
         mutex_lock(&hugetlb_instantiation_mutex);
         entry = huge_ptep_get(ptep);
         if (huge_pte_none(entry)) {
                 ret = hugetlb_no_page(mm, vma, address, ptep, flags);
                 goto out_mutex;
         }
 
         ret = 0;
 
         /*
          * If we are going to COW the mapping later, we examine the pending
          * reservations for this page now. This will ensure that any
          * allocations necessary to record that reservation occur outside the
          * spinlock. For private mappings, we also lookup the pagecache
          * page now as it is used to determine if a reservation has been
          * consumed.
          */
         if ((flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
                 if (vma_needs_reservation(h, vma, address) < 0) {
                         ret = VM_FAULT_OOM;
                         goto out_mutex;
                 }
 
                 if (!(vma->vm_flags & VM_MAYSHARE))
                         pagecache_page = hugetlbfs_pagecache_page(h,
                                                                 vma, address);
         }
 
         /*
          * hugetlb_cow() requires page locks of pte_page(entry) and
          * pagecache_page, so here we need take the former one
          * when page != pagecache_page or !pagecache_page.
          * Note that locking order is always pagecache_page -> page,
          * so no worry about deadlock.
          */
         page = pte_page(entry);
         get_page(page);
         if (page != pagecache_page)
                 lock_page(page);
 
         spin_lock(&mm->page_table_lock);
         /* Check for a racing update before calling hugetlb_cow */
         if (unlikely(!pte_same(entry, huge_ptep_get(ptep))))
                 goto out_page_table_lock;
 
 
         if (flags & FAULT_FLAG_WRITE) {
                 if (!huge_pte_write(entry)) {
                         ret = hugetlb_cow(mm, vma, address, ptep, entry,
                                                         pagecache_page);
                         goto out_page_table_lock;
                 }
                 entry = huge_pte_mkdirty(entry);
         }
         entry = pte_mkyoung(entry);
         if (huge_ptep_set_access_flags(vma, address, ptep, entry,
                                                 flags & FAULT_FLAG_WRITE))
                 update_mmu_cache(vma, address, ptep);
 
 out_page_table_lock:
         spin_unlock(&mm->page_table_lock);
 
         if (pagecache_page) {
                 unlock_page(pagecache_page);
                 put_page(pagecache_page);
         }
         if (page != pagecache_page)
                 unlock_page(page);
         put_page(page);
 
 out_mutex:
         mutex_unlock(&hugetlb_instantiation_mutex);
 
         return ret;
 }
 
 /* Can be overriden by architectures */
 __attribute__((weak)) struct page *
 follow_huge_pud(struct mm_struct *mm, unsigned long address,
                pud_t *pud, int write)
 {
         BUG();
         return NULL;
 }
 
 long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
                          struct page **pages, struct vm_area_struct **vmas,
                          unsigned long *position, unsigned long *nr_pages,
                          long i, unsigned int flags)
 {
         unsigned long pfn_offset;
         unsigned long vaddr = *position;
         unsigned long remainder = *nr_pages;
         struct hstate *h = hstate_vma(vma);
 
         spin_lock(&mm->page_table_lock);
         while (vaddr < vma->vm_end && remainder) {
                 pte_t *pte;
                 int absent;
                 struct page *page;
 
                 /*
                  * Some archs (sparc64, sh*) have multiple pte_ts to
                  * each hugepage.  We have to make sure we get the
                  * first, for the page indexing below to work.
                  */
                 pte = huge_pte_offset(mm, vaddr & huge_page_mask(h));
                 absent = !pte || huge_pte_none(huge_ptep_get(pte));
 
                 /*
                  * When coredumping, it suits get_dump_page if we just return
                  * an error where there's an empty slot with no huge pagecache
                  * to back it.  This way, we avoid allocating a hugepage, and
                  * the sparse dumpfile avoids allocating disk blocks, but its
                  * huge holes still show up with zeroes where they need to be.
                  */
                 if (absent && (flags & FOLL_DUMP) &&
                     !hugetlbfs_pagecache_present(h, vma, vaddr)) {
                         remainder = 0;
                         break;
                 }
 
                 /*
                  * We need call hugetlb_fault for both hugepages under migration
                  * (in which case hugetlb_fault waits for the migration,) and
                  * hwpoisoned hugepages (in which case we need to prevent the
                  * caller from accessing to them.) In order to do this, we use
                  * here is_swap_pte instead of is_hugetlb_entry_migration and
                  * is_hugetlb_entry_hwpoisoned. This is because it simply covers
                  * both cases, and because we can't follow correct pages
                  * directly from any kind of swap entries.
                  */
                 if (absent || is_swap_pte(huge_ptep_get(pte)) ||
                     ((flags & FOLL_WRITE) &&
                       !huge_pte_write(huge_ptep_get(pte)))) {
                         int ret;
 
                         spin_unlock(&mm->page_table_lock);
                         ret = hugetlb_fault(mm, vma, vaddr,
                                 (flags & FOLL_WRITE) ? FAULT_FLAG_WRITE : 0);
                         spin_lock(&mm->page_table_lock);
                         if (!(ret & VM_FAULT_ERROR))
                                 continue;
 
                         remainder = 0;
                         break;
                 }
 
                 pfn_offset = (vaddr & ~huge_page_mask(h)) >> PAGE_SHIFT;
                 page = pte_page(huge_ptep_get(pte));
 same_page:
                 if (pages) {
                         pages[i] = mem_map_offset(page, pfn_offset);
                         get_page(pages[i]);
                 }
 
                 if (vmas)
                         vmas[i] = vma;
 
                 vaddr += PAGE_SIZE;
                 ++pfn_offset;
                 --remainder;
                 ++i;
                 if (vaddr < vma->vm_end && remainder &&
                                 pfn_offset < pages_per_huge_page(h)) {
                         /*
                          * We use pfn_offset to avoid touching the pageframes
                          * of this compound page.
                          */
                         goto same_page;
                 }
         }
         spin_unlock(&mm->page_table_lock);
         *nr_pages = remainder;
         *position = vaddr;
 
         return i ? i : -EFAULT;
 }
 
 unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
                 unsigned long address, unsigned long end, pgprot_t newprot)
 {
         struct mm_struct *mm = vma->vm_mm;
         unsigned long start = address;
         pte_t *ptep;
         pte_t pte;
         struct hstate *h = hstate_vma(vma);
         unsigned long pages = 0;
 
         BUG_ON(address >= end);
         flush_cache_range(vma, address, end);
 
         mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex);
         spin_lock(&mm->page_table_lock);
         for (; address < end; address += huge_page_size(h)) {
                 ptep = huge_pte_offset(mm, address);
                 if (!ptep)
                         continue;
                 if (huge_pmd_unshare(mm, &address, ptep)) {
                         pages++;
                         continue;
                 }
                 if (!huge_pte_none(huge_ptep_get(ptep))) {
                         pte = huge_ptep_get_and_clear(mm, address, ptep);
                         pte = pte_mkhuge(huge_pte_modify(pte, newprot));
                         pte = arch_make_huge_pte(pte, vma, NULL, 0);
                         set_huge_pte_at(mm, address, ptep, pte);
                         pages++;
                 }
         }
         spin_unlock(&mm->page_table_lock);
         /*
          * Must flush TLB before releasing i_mmap_mutex: x86's huge_pmd_unshare
          * may have cleared our pud entry and done put_page on the page table:
          * once we release i_mmap_mutex, another task can do the final put_page
          * and that page table be reused and filled with junk.
          */
         flush_tlb_range(vma, start, end);
         mutex_unlock(&vma->vm_file->f_mapping->i_mmap_mutex);
 
         return pages << h->order;
 }
 
 int hugetlb_reserve_pages(struct inode *inode,
                                         long from, long to,
                                         struct vm_area_struct *vma,
                                         vm_flags_t vm_flags)
 {
         long ret, chg;
         struct hstate *h = hstate_inode(inode);
         struct hugepage_subpool *spool = subpool_inode(inode);
 
         /*
          * Only apply hugepage reservation if asked. At fault time, an
          * attempt will be made for VM_NORESERVE to allocate a page
          * without using reserves
          */
         if (vm_flags & VM_NORESERVE)
                 return 0;
 
         /*
          * Shared mappings base their reservation on the number of pages that
          * are already allocated on behalf of the file. Private mappings need
          * to reserve the full area even if read-only as mprotect() may be
          * called to make the mapping read-write. Assume !vma is a shm mapping
          */
         if (!vma || vma->vm_flags & VM_MAYSHARE)
                 chg = region_chg(&inode->i_mapping->private_list, from, to);
         else {
                 struct resv_map *resv_map = resv_map_alloc();
                 if (!resv_map)
                         return -ENOMEM;
 
                 chg = to - from;
 
                 set_vma_resv_map(vma, resv_map);
                 set_vma_resv_flags(vma, HPAGE_RESV_OWNER);
         }
 
         if (chg < 0) {
                 ret = chg;
                 goto out_err;
         }
 
         /* There must be enough pages in the subpool for the mapping */
         if (hugepage_subpool_get_pages(spool, chg)) {
                 ret = -ENOSPC;
                 goto out_err;
         }
 
         /*
          * Check enough hugepages are available for the reservation.
          * Hand the pages back to the subpool if there are not
          */
         ret = hugetlb_acct_memory(h, chg);
         if (ret < 0) {
                 hugepage_subpool_put_pages(spool, chg);
                 goto out_err;
         }
 
         /*
          * Account for the reservations made. Shared mappings record regions
          * that have reservations as they are shared by multiple VMAs.
          * When the last VMA disappears, the region map says how much
          * the reservation was and the page cache tells how much of
          * the reservation was consumed. Private mappings are per-VMA and
          * only the consumed reservations are tracked. When the VMA
          * disappears, the original reservation is the VMA size and the
          * consumed reservations are stored in the map. Hence, nothing
          * else has to be done for private mappings here
          */
         if (!vma || vma->vm_flags & VM_MAYSHARE)
                 region_add(&inode->i_mapping->private_list, from, to);
         return 0;
 out_err:
         if (vma)
                 resv_map_put(vma);
         return ret;
 }
 
 void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed)
 {
         struct hstate *h = hstate_inode(inode);
         long chg = region_truncate(&inode->i_mapping->private_list, offset);
         struct hugepage_subpool *spool = subpool_inode(inode);
 
         spin_lock(&inode->i_lock);
         inode->i_blocks -= (blocks_per_huge_page(h) * freed);
         spin_unlock(&inode->i_lock);
 
         hugepage_subpool_put_pages(spool, (chg - freed));
         hugetlb_acct_memory(h, -(chg - freed));
 }
 
 #ifdef CONFIG_MEMORY_FAILURE
 
 /* Should be called in hugetlb_lock */
 static int is_hugepage_on_freelist(struct page *hpage)
 {
         struct page *page;
         struct page *tmp;
         struct hstate *h = page_hstate(hpage);
         int nid = page_to_nid(hpage);
 
         list_for_each_entry_safe(page, tmp, &h->hugepage_freelists[nid], lru)
                 if (page == hpage)
                         return 1;
         return 0;
 }
 
 /*
  * This function is called from memory failure code.
  * Assume the caller holds page lock of the head page.
  */
 int dequeue_hwpoisoned_huge_page(struct page *hpage)
 {
         struct hstate *h = page_hstate(hpage);
         int nid = page_to_nid(hpage);
         int ret = -EBUSY;
 
         spin_lock(&hugetlb_lock);
         if (is_hugepage_on_freelist(hpage)) {
                 /*
                  * Hwpoisoned hugepage isn't linked to activelist or freelist,
                  * but dangling hpage->lru can trigger list-debug warnings
                  * (this happens when we call unpoison_memory() on it),
                  * so let it point to itself with list_del_init().
                  */
                 list_del_init(&hpage->lru);
                 set_page_refcounted(hpage);
                 h->free_huge_pages--;
                 h->free_huge_pages_node[nid]--;
                 ret = 0;
         }
         spin_unlock(&hugetlb_lock);
         return ret;
 }
 #endif
 

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