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TOMOYO Linux Cross Reference
Linux/mm/zsmalloc.c

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  1 /*
  2  * zsmalloc memory allocator
  3  *
  4  * Copyright (C) 2011  Nitin Gupta
  5  * Copyright (C) 2012, 2013 Minchan Kim
  6  *
  7  * This code is released using a dual license strategy: BSD/GPL
  8  * You can choose the license that better fits your requirements.
  9  *
 10  * Released under the terms of 3-clause BSD License
 11  * Released under the terms of GNU General Public License Version 2.0
 12  */
 13 
 14 /*
 15  * This allocator is designed for use with zram. Thus, the allocator is
 16  * supposed to work well under low memory conditions. In particular, it
 17  * never attempts higher order page allocation which is very likely to
 18  * fail under memory pressure. On the other hand, if we just use single
 19  * (0-order) pages, it would suffer from very high fragmentation --
 20  * any object of size PAGE_SIZE/2 or larger would occupy an entire page.
 21  * This was one of the major issues with its predecessor (xvmalloc).
 22  *
 23  * To overcome these issues, zsmalloc allocates a bunch of 0-order pages
 24  * and links them together using various 'struct page' fields. These linked
 25  * pages act as a single higher-order page i.e. an object can span 0-order
 26  * page boundaries. The code refers to these linked pages as a single entity
 27  * called zspage.
 28  *
 29  * For simplicity, zsmalloc can only allocate objects of size up to PAGE_SIZE
 30  * since this satisfies the requirements of all its current users (in the
 31  * worst case, page is incompressible and is thus stored "as-is" i.e. in
 32  * uncompressed form). For allocation requests larger than this size, failure
 33  * is returned (see zs_malloc).
 34  *
 35  * Additionally, zs_malloc() does not return a dereferenceable pointer.
 36  * Instead, it returns an opaque handle (unsigned long) which encodes actual
 37  * location of the allocated object. The reason for this indirection is that
 38  * zsmalloc does not keep zspages permanently mapped since that would cause
 39  * issues on 32-bit systems where the VA region for kernel space mappings
 40  * is very small. So, before using the allocating memory, the object has to
 41  * be mapped using zs_map_object() to get a usable pointer and subsequently
 42  * unmapped using zs_unmap_object().
 43  *
 44  * Following is how we use various fields and flags of underlying
 45  * struct page(s) to form a zspage.
 46  *
 47  * Usage of struct page fields:
 48  *      page->first_page: points to the first component (0-order) page
 49  *      page->index (union with page->freelist): offset of the first object
 50  *              starting in this page. For the first page, this is
 51  *              always 0, so we use this field (aka freelist) to point
 52  *              to the first free object in zspage.
 53  *      page->lru: links together all component pages (except the first page)
 54  *              of a zspage
 55  *
 56  *      For _first_ page only:
 57  *
 58  *      page->private (union with page->first_page): refers to the
 59  *              component page after the first page
 60  *      page->freelist: points to the first free object in zspage.
 61  *              Free objects are linked together using in-place
 62  *              metadata.
 63  *      page->objects: maximum number of objects we can store in this
 64  *              zspage (class->zspage_order * PAGE_SIZE / class->size)
 65  *      page->lru: links together first pages of various zspages.
 66  *              Basically forming list of zspages in a fullness group.
 67  *      page->mapping: class index and fullness group of the zspage
 68  *
 69  * Usage of struct page flags:
 70  *      PG_private: identifies the first component page
 71  *      PG_private2: identifies the last component page
 72  *
 73  */
 74 
 75 #ifdef CONFIG_ZSMALLOC_DEBUG
 76 #define DEBUG
 77 #endif
 78 
 79 #include <linux/module.h>
 80 #include <linux/kernel.h>
 81 #include <linux/bitops.h>
 82 #include <linux/errno.h>
 83 #include <linux/highmem.h>
 84 #include <linux/string.h>
 85 #include <linux/slab.h>
 86 #include <asm/tlbflush.h>
 87 #include <asm/pgtable.h>
 88 #include <linux/cpumask.h>
 89 #include <linux/cpu.h>
 90 #include <linux/vmalloc.h>
 91 #include <linux/hardirq.h>
 92 #include <linux/spinlock.h>
 93 #include <linux/types.h>
 94 #include <linux/zsmalloc.h>
 95 
 96 /*
 97  * This must be power of 2 and greater than of equal to sizeof(link_free).
 98  * These two conditions ensure that any 'struct link_free' itself doesn't
 99  * span more than 1 page which avoids complex case of mapping 2 pages simply
100  * to restore link_free pointer values.
101  */
102 #define ZS_ALIGN                8
103 
104 /*
105  * A single 'zspage' is composed of up to 2^N discontiguous 0-order (single)
106  * pages. ZS_MAX_ZSPAGE_ORDER defines upper limit on N.
107  */
108 #define ZS_MAX_ZSPAGE_ORDER 2
109 #define ZS_MAX_PAGES_PER_ZSPAGE (_AC(1, UL) << ZS_MAX_ZSPAGE_ORDER)
110 
111 /*
112  * Object location (<PFN>, <obj_idx>) is encoded as
113  * as single (unsigned long) handle value.
114  *
115  * Note that object index <obj_idx> is relative to system
116  * page <PFN> it is stored in, so for each sub-page belonging
117  * to a zspage, obj_idx starts with 0.
118  *
119  * This is made more complicated by various memory models and PAE.
120  */
121 
122 #ifndef MAX_PHYSMEM_BITS
123 #ifdef CONFIG_HIGHMEM64G
124 #define MAX_PHYSMEM_BITS 36
125 #else /* !CONFIG_HIGHMEM64G */
126 /*
127  * If this definition of MAX_PHYSMEM_BITS is used, OBJ_INDEX_BITS will just
128  * be PAGE_SHIFT
129  */
130 #define MAX_PHYSMEM_BITS BITS_PER_LONG
131 #endif
132 #endif
133 #define _PFN_BITS               (MAX_PHYSMEM_BITS - PAGE_SHIFT)
134 #define OBJ_INDEX_BITS  (BITS_PER_LONG - _PFN_BITS)
135 #define OBJ_INDEX_MASK  ((_AC(1, UL) << OBJ_INDEX_BITS) - 1)
136 
137 #define MAX(a, b) ((a) >= (b) ? (a) : (b))
138 /* ZS_MIN_ALLOC_SIZE must be multiple of ZS_ALIGN */
139 #define ZS_MIN_ALLOC_SIZE \
140         MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS))
141 #define ZS_MAX_ALLOC_SIZE       PAGE_SIZE
142 
143 /*
144  * On systems with 4K page size, this gives 254 size classes! There is a
145  * trader-off here:
146  *  - Large number of size classes is potentially wasteful as free page are
147  *    spread across these classes
148  *  - Small number of size classes causes large internal fragmentation
149  *  - Probably its better to use specific size classes (empirically
150  *    determined). NOTE: all those class sizes must be set as multiple of
151  *    ZS_ALIGN to make sure link_free itself never has to span 2 pages.
152  *
153  *  ZS_MIN_ALLOC_SIZE and ZS_SIZE_CLASS_DELTA must be multiple of ZS_ALIGN
154  *  (reason above)
155  */
156 #define ZS_SIZE_CLASS_DELTA     (PAGE_SIZE >> 8)
157 #define ZS_SIZE_CLASSES         ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / \
158                                         ZS_SIZE_CLASS_DELTA + 1)
159 
160 /*
161  * We do not maintain any list for completely empty or full pages
162  */
163 enum fullness_group {
164         ZS_ALMOST_FULL,
165         ZS_ALMOST_EMPTY,
166         _ZS_NR_FULLNESS_GROUPS,
167 
168         ZS_EMPTY,
169         ZS_FULL
170 };
171 
172 /*
173  * We assign a page to ZS_ALMOST_EMPTY fullness group when:
174  *      n <= N / f, where
175  * n = number of allocated objects
176  * N = total number of objects zspage can store
177  * f = 1/fullness_threshold_frac
178  *
179  * Similarly, we assign zspage to:
180  *      ZS_ALMOST_FULL  when n > N / f
181  *      ZS_EMPTY        when n == 0
182  *      ZS_FULL         when n == N
183  *
184  * (see: fix_fullness_group())
185  */
186 static const int fullness_threshold_frac = 4;
187 
188 struct size_class {
189         /*
190          * Size of objects stored in this class. Must be multiple
191          * of ZS_ALIGN.
192          */
193         int size;
194         unsigned int index;
195 
196         /* Number of PAGE_SIZE sized pages to combine to form a 'zspage' */
197         int pages_per_zspage;
198 
199         spinlock_t lock;
200 
201         /* stats */
202         u64 pages_allocated;
203 
204         struct page *fullness_list[_ZS_NR_FULLNESS_GROUPS];
205 };
206 
207 /*
208  * Placed within free objects to form a singly linked list.
209  * For every zspage, first_page->freelist gives head of this list.
210  *
211  * This must be power of 2 and less than or equal to ZS_ALIGN
212  */
213 struct link_free {
214         /* Handle of next free chunk (encodes <PFN, obj_idx>) */
215         void *next;
216 };
217 
218 struct zs_pool {
219         struct size_class size_class[ZS_SIZE_CLASSES];
220 
221         gfp_t flags;    /* allocation flags used when growing pool */
222 };
223 
224 /*
225  * A zspage's class index and fullness group
226  * are encoded in its (first)page->mapping
227  */
228 #define CLASS_IDX_BITS  28
229 #define FULLNESS_BITS   4
230 #define CLASS_IDX_MASK  ((1 << CLASS_IDX_BITS) - 1)
231 #define FULLNESS_MASK   ((1 << FULLNESS_BITS) - 1)
232 
233 struct mapping_area {
234 #ifdef CONFIG_PGTABLE_MAPPING
235         struct vm_struct *vm; /* vm area for mapping object that span pages */
236 #else
237         char *vm_buf; /* copy buffer for objects that span pages */
238 #endif
239         char *vm_addr; /* address of kmap_atomic()'ed pages */
240         enum zs_mapmode vm_mm; /* mapping mode */
241 };
242 
243 
244 /* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
245 static DEFINE_PER_CPU(struct mapping_area, zs_map_area);
246 
247 static int is_first_page(struct page *page)
248 {
249         return PagePrivate(page);
250 }
251 
252 static int is_last_page(struct page *page)
253 {
254         return PagePrivate2(page);
255 }
256 
257 static void get_zspage_mapping(struct page *page, unsigned int *class_idx,
258                                 enum fullness_group *fullness)
259 {
260         unsigned long m;
261         BUG_ON(!is_first_page(page));
262 
263         m = (unsigned long)page->mapping;
264         *fullness = m & FULLNESS_MASK;
265         *class_idx = (m >> FULLNESS_BITS) & CLASS_IDX_MASK;
266 }
267 
268 static void set_zspage_mapping(struct page *page, unsigned int class_idx,
269                                 enum fullness_group fullness)
270 {
271         unsigned long m;
272         BUG_ON(!is_first_page(page));
273 
274         m = ((class_idx & CLASS_IDX_MASK) << FULLNESS_BITS) |
275                         (fullness & FULLNESS_MASK);
276         page->mapping = (struct address_space *)m;
277 }
278 
279 /*
280  * zsmalloc divides the pool into various size classes where each
281  * class maintains a list of zspages where each zspage is divided
282  * into equal sized chunks. Each allocation falls into one of these
283  * classes depending on its size. This function returns index of the
284  * size class which has chunk size big enough to hold the give size.
285  */
286 static int get_size_class_index(int size)
287 {
288         int idx = 0;
289 
290         if (likely(size > ZS_MIN_ALLOC_SIZE))
291                 idx = DIV_ROUND_UP(size - ZS_MIN_ALLOC_SIZE,
292                                 ZS_SIZE_CLASS_DELTA);
293 
294         return idx;
295 }
296 
297 /*
298  * For each size class, zspages are divided into different groups
299  * depending on how "full" they are. This was done so that we could
300  * easily find empty or nearly empty zspages when we try to shrink
301  * the pool (not yet implemented). This function returns fullness
302  * status of the given page.
303  */
304 static enum fullness_group get_fullness_group(struct page *page)
305 {
306         int inuse, max_objects;
307         enum fullness_group fg;
308         BUG_ON(!is_first_page(page));
309 
310         inuse = page->inuse;
311         max_objects = page->objects;
312 
313         if (inuse == 0)
314                 fg = ZS_EMPTY;
315         else if (inuse == max_objects)
316                 fg = ZS_FULL;
317         else if (inuse <= max_objects / fullness_threshold_frac)
318                 fg = ZS_ALMOST_EMPTY;
319         else
320                 fg = ZS_ALMOST_FULL;
321 
322         return fg;
323 }
324 
325 /*
326  * Each size class maintains various freelists and zspages are assigned
327  * to one of these freelists based on the number of live objects they
328  * have. This functions inserts the given zspage into the freelist
329  * identified by <class, fullness_group>.
330  */
331 static void insert_zspage(struct page *page, struct size_class *class,
332                                 enum fullness_group fullness)
333 {
334         struct page **head;
335 
336         BUG_ON(!is_first_page(page));
337 
338         if (fullness >= _ZS_NR_FULLNESS_GROUPS)
339                 return;
340 
341         head = &class->fullness_list[fullness];
342         if (*head)
343                 list_add_tail(&page->lru, &(*head)->lru);
344 
345         *head = page;
346 }
347 
348 /*
349  * This function removes the given zspage from the freelist identified
350  * by <class, fullness_group>.
351  */
352 static void remove_zspage(struct page *page, struct size_class *class,
353                                 enum fullness_group fullness)
354 {
355         struct page **head;
356 
357         BUG_ON(!is_first_page(page));
358 
359         if (fullness >= _ZS_NR_FULLNESS_GROUPS)
360                 return;
361 
362         head = &class->fullness_list[fullness];
363         BUG_ON(!*head);
364         if (list_empty(&(*head)->lru))
365                 *head = NULL;
366         else if (*head == page)
367                 *head = (struct page *)list_entry((*head)->lru.next,
368                                         struct page, lru);
369 
370         list_del_init(&page->lru);
371 }
372 
373 /*
374  * Each size class maintains zspages in different fullness groups depending
375  * on the number of live objects they contain. When allocating or freeing
376  * objects, the fullness status of the page can change, say, from ALMOST_FULL
377  * to ALMOST_EMPTY when freeing an object. This function checks if such
378  * a status change has occurred for the given page and accordingly moves the
379  * page from the freelist of the old fullness group to that of the new
380  * fullness group.
381  */
382 static enum fullness_group fix_fullness_group(struct zs_pool *pool,
383                                                 struct page *page)
384 {
385         int class_idx;
386         struct size_class *class;
387         enum fullness_group currfg, newfg;
388 
389         BUG_ON(!is_first_page(page));
390 
391         get_zspage_mapping(page, &class_idx, &currfg);
392         newfg = get_fullness_group(page);
393         if (newfg == currfg)
394                 goto out;
395 
396         class = &pool->size_class[class_idx];
397         remove_zspage(page, class, currfg);
398         insert_zspage(page, class, newfg);
399         set_zspage_mapping(page, class_idx, newfg);
400 
401 out:
402         return newfg;
403 }
404 
405 /*
406  * We have to decide on how many pages to link together
407  * to form a zspage for each size class. This is important
408  * to reduce wastage due to unusable space left at end of
409  * each zspage which is given as:
410  *      wastage = Zp - Zp % size_class
411  * where Zp = zspage size = k * PAGE_SIZE where k = 1, 2, ...
412  *
413  * For example, for size class of 3/8 * PAGE_SIZE, we should
414  * link together 3 PAGE_SIZE sized pages to form a zspage
415  * since then we can perfectly fit in 8 such objects.
416  */
417 static int get_pages_per_zspage(int class_size)
418 {
419         int i, max_usedpc = 0;
420         /* zspage order which gives maximum used size per KB */
421         int max_usedpc_order = 1;
422 
423         for (i = 1; i <= ZS_MAX_PAGES_PER_ZSPAGE; i++) {
424                 int zspage_size;
425                 int waste, usedpc;
426 
427                 zspage_size = i * PAGE_SIZE;
428                 waste = zspage_size % class_size;
429                 usedpc = (zspage_size - waste) * 100 / zspage_size;
430 
431                 if (usedpc > max_usedpc) {
432                         max_usedpc = usedpc;
433                         max_usedpc_order = i;
434                 }
435         }
436 
437         return max_usedpc_order;
438 }
439 
440 /*
441  * A single 'zspage' is composed of many system pages which are
442  * linked together using fields in struct page. This function finds
443  * the first/head page, given any component page of a zspage.
444  */
445 static struct page *get_first_page(struct page *page)
446 {
447         if (is_first_page(page))
448                 return page;
449         else
450                 return page->first_page;
451 }
452 
453 static struct page *get_next_page(struct page *page)
454 {
455         struct page *next;
456 
457         if (is_last_page(page))
458                 next = NULL;
459         else if (is_first_page(page))
460                 next = (struct page *)page_private(page);
461         else
462                 next = list_entry(page->lru.next, struct page, lru);
463 
464         return next;
465 }
466 
467 /*
468  * Encode <page, obj_idx> as a single handle value.
469  * On hardware platforms with physical memory starting at 0x0 the pfn
470  * could be 0 so we ensure that the handle will never be 0 by adjusting the
471  * encoded obj_idx value before encoding.
472  */
473 static void *obj_location_to_handle(struct page *page, unsigned long obj_idx)
474 {
475         unsigned long handle;
476 
477         if (!page) {
478                 BUG_ON(obj_idx);
479                 return NULL;
480         }
481 
482         handle = page_to_pfn(page) << OBJ_INDEX_BITS;
483         handle |= ((obj_idx + 1) & OBJ_INDEX_MASK);
484 
485         return (void *)handle;
486 }
487 
488 /*
489  * Decode <page, obj_idx> pair from the given object handle. We adjust the
490  * decoded obj_idx back to its original value since it was adjusted in
491  * obj_location_to_handle().
492  */
493 static void obj_handle_to_location(unsigned long handle, struct page **page,
494                                 unsigned long *obj_idx)
495 {
496         *page = pfn_to_page(handle >> OBJ_INDEX_BITS);
497         *obj_idx = (handle & OBJ_INDEX_MASK) - 1;
498 }
499 
500 static unsigned long obj_idx_to_offset(struct page *page,
501                                 unsigned long obj_idx, int class_size)
502 {
503         unsigned long off = 0;
504 
505         if (!is_first_page(page))
506                 off = page->index;
507 
508         return off + obj_idx * class_size;
509 }
510 
511 static void reset_page(struct page *page)
512 {
513         clear_bit(PG_private, &page->flags);
514         clear_bit(PG_private_2, &page->flags);
515         set_page_private(page, 0);
516         page->mapping = NULL;
517         page->freelist = NULL;
518         page_mapcount_reset(page);
519 }
520 
521 static void free_zspage(struct page *first_page)
522 {
523         struct page *nextp, *tmp, *head_extra;
524 
525         BUG_ON(!is_first_page(first_page));
526         BUG_ON(first_page->inuse);
527 
528         head_extra = (struct page *)page_private(first_page);
529 
530         reset_page(first_page);
531         __free_page(first_page);
532 
533         /* zspage with only 1 system page */
534         if (!head_extra)
535                 return;
536 
537         list_for_each_entry_safe(nextp, tmp, &head_extra->lru, lru) {
538                 list_del(&nextp->lru);
539                 reset_page(nextp);
540                 __free_page(nextp);
541         }
542         reset_page(head_extra);
543         __free_page(head_extra);
544 }
545 
546 /* Initialize a newly allocated zspage */
547 static void init_zspage(struct page *first_page, struct size_class *class)
548 {
549         unsigned long off = 0;
550         struct page *page = first_page;
551 
552         BUG_ON(!is_first_page(first_page));
553         while (page) {
554                 struct page *next_page;
555                 struct link_free *link;
556                 unsigned int i, objs_on_page;
557 
558                 /*
559                  * page->index stores offset of first object starting
560                  * in the page. For the first page, this is always 0,
561                  * so we use first_page->index (aka ->freelist) to store
562                  * head of corresponding zspage's freelist.
563                  */
564                 if (page != first_page)
565                         page->index = off;
566 
567                 link = (struct link_free *)kmap_atomic(page) +
568                                                 off / sizeof(*link);
569                 objs_on_page = (PAGE_SIZE - off) / class->size;
570 
571                 for (i = 1; i <= objs_on_page; i++) {
572                         off += class->size;
573                         if (off < PAGE_SIZE) {
574                                 link->next = obj_location_to_handle(page, i);
575                                 link += class->size / sizeof(*link);
576                         }
577                 }
578 
579                 /*
580                  * We now come to the last (full or partial) object on this
581                  * page, which must point to the first object on the next
582                  * page (if present)
583                  */
584                 next_page = get_next_page(page);
585                 link->next = obj_location_to_handle(next_page, 0);
586                 kunmap_atomic(link);
587                 page = next_page;
588                 off = (off + class->size) % PAGE_SIZE;
589         }
590 }
591 
592 /*
593  * Allocate a zspage for the given size class
594  */
595 static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
596 {
597         int i, error;
598         struct page *first_page = NULL, *uninitialized_var(prev_page);
599 
600         /*
601          * Allocate individual pages and link them together as:
602          * 1. first page->private = first sub-page
603          * 2. all sub-pages are linked together using page->lru
604          * 3. each sub-page is linked to the first page using page->first_page
605          *
606          * For each size class, First/Head pages are linked together using
607          * page->lru. Also, we set PG_private to identify the first page
608          * (i.e. no other sub-page has this flag set) and PG_private_2 to
609          * identify the last page.
610          */
611         error = -ENOMEM;
612         for (i = 0; i < class->pages_per_zspage; i++) {
613                 struct page *page;
614 
615                 page = alloc_page(flags);
616                 if (!page)
617                         goto cleanup;
618 
619                 INIT_LIST_HEAD(&page->lru);
620                 if (i == 0) {   /* first page */
621                         SetPagePrivate(page);
622                         set_page_private(page, 0);
623                         first_page = page;
624                         first_page->inuse = 0;
625                 }
626                 if (i == 1)
627                         set_page_private(first_page, (unsigned long)page);
628                 if (i >= 1)
629                         page->first_page = first_page;
630                 if (i >= 2)
631                         list_add(&page->lru, &prev_page->lru);
632                 if (i == class->pages_per_zspage - 1)   /* last page */
633                         SetPagePrivate2(page);
634                 prev_page = page;
635         }
636 
637         init_zspage(first_page, class);
638 
639         first_page->freelist = obj_location_to_handle(first_page, 0);
640         /* Maximum number of objects we can store in this zspage */
641         first_page->objects = class->pages_per_zspage * PAGE_SIZE / class->size;
642 
643         error = 0; /* Success */
644 
645 cleanup:
646         if (unlikely(error) && first_page) {
647                 free_zspage(first_page);
648                 first_page = NULL;
649         }
650 
651         return first_page;
652 }
653 
654 static struct page *find_get_zspage(struct size_class *class)
655 {
656         int i;
657         struct page *page;
658 
659         for (i = 0; i < _ZS_NR_FULLNESS_GROUPS; i++) {
660                 page = class->fullness_list[i];
661                 if (page)
662                         break;
663         }
664 
665         return page;
666 }
667 
668 #ifdef CONFIG_PGTABLE_MAPPING
669 static inline int __zs_cpu_up(struct mapping_area *area)
670 {
671         /*
672          * Make sure we don't leak memory if a cpu UP notification
673          * and zs_init() race and both call zs_cpu_up() on the same cpu
674          */
675         if (area->vm)
676                 return 0;
677         area->vm = alloc_vm_area(PAGE_SIZE * 2, NULL);
678         if (!area->vm)
679                 return -ENOMEM;
680         return 0;
681 }
682 
683 static inline void __zs_cpu_down(struct mapping_area *area)
684 {
685         if (area->vm)
686                 free_vm_area(area->vm);
687         area->vm = NULL;
688 }
689 
690 static inline void *__zs_map_object(struct mapping_area *area,
691                                 struct page *pages[2], int off, int size)
692 {
693         BUG_ON(map_vm_area(area->vm, PAGE_KERNEL, &pages));
694         area->vm_addr = area->vm->addr;
695         return area->vm_addr + off;
696 }
697 
698 static inline void __zs_unmap_object(struct mapping_area *area,
699                                 struct page *pages[2], int off, int size)
700 {
701         unsigned long addr = (unsigned long)area->vm_addr;
702 
703         unmap_kernel_range(addr, PAGE_SIZE * 2);
704 }
705 
706 #else /* CONFIG_PGTABLE_MAPPING */
707 
708 static inline int __zs_cpu_up(struct mapping_area *area)
709 {
710         /*
711          * Make sure we don't leak memory if a cpu UP notification
712          * and zs_init() race and both call zs_cpu_up() on the same cpu
713          */
714         if (area->vm_buf)
715                 return 0;
716         area->vm_buf = (char *)__get_free_page(GFP_KERNEL);
717         if (!area->vm_buf)
718                 return -ENOMEM;
719         return 0;
720 }
721 
722 static inline void __zs_cpu_down(struct mapping_area *area)
723 {
724         if (area->vm_buf)
725                 free_page((unsigned long)area->vm_buf);
726         area->vm_buf = NULL;
727 }
728 
729 static void *__zs_map_object(struct mapping_area *area,
730                         struct page *pages[2], int off, int size)
731 {
732         int sizes[2];
733         void *addr;
734         char *buf = area->vm_buf;
735 
736         /* disable page faults to match kmap_atomic() return conditions */
737         pagefault_disable();
738 
739         /* no read fastpath */
740         if (area->vm_mm == ZS_MM_WO)
741                 goto out;
742 
743         sizes[0] = PAGE_SIZE - off;
744         sizes[1] = size - sizes[0];
745 
746         /* copy object to per-cpu buffer */
747         addr = kmap_atomic(pages[0]);
748         memcpy(buf, addr + off, sizes[0]);
749         kunmap_atomic(addr);
750         addr = kmap_atomic(pages[1]);
751         memcpy(buf + sizes[0], addr, sizes[1]);
752         kunmap_atomic(addr);
753 out:
754         return area->vm_buf;
755 }
756 
757 static void __zs_unmap_object(struct mapping_area *area,
758                         struct page *pages[2], int off, int size)
759 {
760         int sizes[2];
761         void *addr;
762         char *buf = area->vm_buf;
763 
764         /* no write fastpath */
765         if (area->vm_mm == ZS_MM_RO)
766                 goto out;
767 
768         sizes[0] = PAGE_SIZE - off;
769         sizes[1] = size - sizes[0];
770 
771         /* copy per-cpu buffer to object */
772         addr = kmap_atomic(pages[0]);
773         memcpy(addr + off, buf, sizes[0]);
774         kunmap_atomic(addr);
775         addr = kmap_atomic(pages[1]);
776         memcpy(addr, buf + sizes[0], sizes[1]);
777         kunmap_atomic(addr);
778 
779 out:
780         /* enable page faults to match kunmap_atomic() return conditions */
781         pagefault_enable();
782 }
783 
784 #endif /* CONFIG_PGTABLE_MAPPING */
785 
786 static int zs_cpu_notifier(struct notifier_block *nb, unsigned long action,
787                                 void *pcpu)
788 {
789         int ret, cpu = (long)pcpu;
790         struct mapping_area *area;
791 
792         switch (action) {
793         case CPU_UP_PREPARE:
794                 area = &per_cpu(zs_map_area, cpu);
795                 ret = __zs_cpu_up(area);
796                 if (ret)
797                         return notifier_from_errno(ret);
798                 break;
799         case CPU_DEAD:
800         case CPU_UP_CANCELED:
801                 area = &per_cpu(zs_map_area, cpu);
802                 __zs_cpu_down(area);
803                 break;
804         }
805 
806         return NOTIFY_OK;
807 }
808 
809 static struct notifier_block zs_cpu_nb = {
810         .notifier_call = zs_cpu_notifier
811 };
812 
813 static void zs_exit(void)
814 {
815         int cpu;
816 
817         cpu_notifier_register_begin();
818 
819         for_each_online_cpu(cpu)
820                 zs_cpu_notifier(NULL, CPU_DEAD, (void *)(long)cpu);
821         __unregister_cpu_notifier(&zs_cpu_nb);
822 
823         cpu_notifier_register_done();
824 }
825 
826 static int zs_init(void)
827 {
828         int cpu, ret;
829 
830         cpu_notifier_register_begin();
831 
832         __register_cpu_notifier(&zs_cpu_nb);
833         for_each_online_cpu(cpu) {
834                 ret = zs_cpu_notifier(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
835                 if (notifier_to_errno(ret)) {
836                         cpu_notifier_register_done();
837                         goto fail;
838                 }
839         }
840 
841         cpu_notifier_register_done();
842 
843         return 0;
844 fail:
845         zs_exit();
846         return notifier_to_errno(ret);
847 }
848 
849 /**
850  * zs_create_pool - Creates an allocation pool to work from.
851  * @flags: allocation flags used to allocate pool metadata
852  *
853  * This function must be called before anything when using
854  * the zsmalloc allocator.
855  *
856  * On success, a pointer to the newly created pool is returned,
857  * otherwise NULL.
858  */
859 struct zs_pool *zs_create_pool(gfp_t flags)
860 {
861         int i, ovhd_size;
862         struct zs_pool *pool;
863 
864         ovhd_size = roundup(sizeof(*pool), PAGE_SIZE);
865         pool = kzalloc(ovhd_size, GFP_KERNEL);
866         if (!pool)
867                 return NULL;
868 
869         for (i = 0; i < ZS_SIZE_CLASSES; i++) {
870                 int size;
871                 struct size_class *class;
872 
873                 size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
874                 if (size > ZS_MAX_ALLOC_SIZE)
875                         size = ZS_MAX_ALLOC_SIZE;
876 
877                 class = &pool->size_class[i];
878                 class->size = size;
879                 class->index = i;
880                 spin_lock_init(&class->lock);
881                 class->pages_per_zspage = get_pages_per_zspage(size);
882 
883         }
884 
885         pool->flags = flags;
886 
887         return pool;
888 }
889 EXPORT_SYMBOL_GPL(zs_create_pool);
890 
891 void zs_destroy_pool(struct zs_pool *pool)
892 {
893         int i;
894 
895         for (i = 0; i < ZS_SIZE_CLASSES; i++) {
896                 int fg;
897                 struct size_class *class = &pool->size_class[i];
898 
899                 for (fg = 0; fg < _ZS_NR_FULLNESS_GROUPS; fg++) {
900                         if (class->fullness_list[fg]) {
901                                 pr_info("Freeing non-empty class with size %db, fullness group %d\n",
902                                         class->size, fg);
903                         }
904                 }
905         }
906         kfree(pool);
907 }
908 EXPORT_SYMBOL_GPL(zs_destroy_pool);
909 
910 /**
911  * zs_malloc - Allocate block of given size from pool.
912  * @pool: pool to allocate from
913  * @size: size of block to allocate
914  *
915  * On success, handle to the allocated object is returned,
916  * otherwise 0.
917  * Allocation requests with size > ZS_MAX_ALLOC_SIZE will fail.
918  */
919 unsigned long zs_malloc(struct zs_pool *pool, size_t size)
920 {
921         unsigned long obj;
922         struct link_free *link;
923         int class_idx;
924         struct size_class *class;
925 
926         struct page *first_page, *m_page;
927         unsigned long m_objidx, m_offset;
928 
929         if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
930                 return 0;
931 
932         class_idx = get_size_class_index(size);
933         class = &pool->size_class[class_idx];
934         BUG_ON(class_idx != class->index);
935 
936         spin_lock(&class->lock);
937         first_page = find_get_zspage(class);
938 
939         if (!first_page) {
940                 spin_unlock(&class->lock);
941                 first_page = alloc_zspage(class, pool->flags);
942                 if (unlikely(!first_page))
943                         return 0;
944 
945                 set_zspage_mapping(first_page, class->index, ZS_EMPTY);
946                 spin_lock(&class->lock);
947                 class->pages_allocated += class->pages_per_zspage;
948         }
949 
950         obj = (unsigned long)first_page->freelist;
951         obj_handle_to_location(obj, &m_page, &m_objidx);
952         m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);
953 
954         link = (struct link_free *)kmap_atomic(m_page) +
955                                         m_offset / sizeof(*link);
956         first_page->freelist = link->next;
957         memset(link, POISON_INUSE, sizeof(*link));
958         kunmap_atomic(link);
959 
960         first_page->inuse++;
961         /* Now move the zspage to another fullness group, if required */
962         fix_fullness_group(pool, first_page);
963         spin_unlock(&class->lock);
964 
965         return obj;
966 }
967 EXPORT_SYMBOL_GPL(zs_malloc);
968 
969 void zs_free(struct zs_pool *pool, unsigned long obj)
970 {
971         struct link_free *link;
972         struct page *first_page, *f_page;
973         unsigned long f_objidx, f_offset;
974 
975         int class_idx;
976         struct size_class *class;
977         enum fullness_group fullness;
978 
979         if (unlikely(!obj))
980                 return;
981 
982         obj_handle_to_location(obj, &f_page, &f_objidx);
983         first_page = get_first_page(f_page);
984 
985         get_zspage_mapping(first_page, &class_idx, &fullness);
986         class = &pool->size_class[class_idx];
987         f_offset = obj_idx_to_offset(f_page, f_objidx, class->size);
988 
989         spin_lock(&class->lock);
990 
991         /* Insert this object in containing zspage's freelist */
992         link = (struct link_free *)((unsigned char *)kmap_atomic(f_page)
993                                                         + f_offset);
994         link->next = first_page->freelist;
995         kunmap_atomic(link);
996         first_page->freelist = (void *)obj;
997 
998         first_page->inuse--;
999         fullness = fix_fullness_group(pool, first_page);
1000 
1001         if (fullness == ZS_EMPTY)
1002                 class->pages_allocated -= class->pages_per_zspage;
1003 
1004         spin_unlock(&class->lock);
1005 
1006         if (fullness == ZS_EMPTY)
1007                 free_zspage(first_page);
1008 }
1009 EXPORT_SYMBOL_GPL(zs_free);
1010 
1011 /**
1012  * zs_map_object - get address of allocated object from handle.
1013  * @pool: pool from which the object was allocated
1014  * @handle: handle returned from zs_malloc
1015  *
1016  * Before using an object allocated from zs_malloc, it must be mapped using
1017  * this function. When done with the object, it must be unmapped using
1018  * zs_unmap_object.
1019  *
1020  * Only one object can be mapped per cpu at a time. There is no protection
1021  * against nested mappings.
1022  *
1023  * This function returns with preemption and page faults disabled.
1024  */
1025 void *zs_map_object(struct zs_pool *pool, unsigned long handle,
1026                         enum zs_mapmode mm)
1027 {
1028         struct page *page;
1029         unsigned long obj_idx, off;
1030 
1031         unsigned int class_idx;
1032         enum fullness_group fg;
1033         struct size_class *class;
1034         struct mapping_area *area;
1035         struct page *pages[2];
1036 
1037         BUG_ON(!handle);
1038 
1039         /*
1040          * Because we use per-cpu mapping areas shared among the
1041          * pools/users, we can't allow mapping in interrupt context
1042          * because it can corrupt another users mappings.
1043          */
1044         BUG_ON(in_interrupt());
1045 
1046         obj_handle_to_location(handle, &page, &obj_idx);
1047         get_zspage_mapping(get_first_page(page), &class_idx, &fg);
1048         class = &pool->size_class[class_idx];
1049         off = obj_idx_to_offset(page, obj_idx, class->size);
1050 
1051         area = &get_cpu_var(zs_map_area);
1052         area->vm_mm = mm;
1053         if (off + class->size <= PAGE_SIZE) {
1054                 /* this object is contained entirely within a page */
1055                 area->vm_addr = kmap_atomic(page);
1056                 return area->vm_addr + off;
1057         }
1058 
1059         /* this object spans two pages */
1060         pages[0] = page;
1061         pages[1] = get_next_page(page);
1062         BUG_ON(!pages[1]);
1063 
1064         return __zs_map_object(area, pages, off, class->size);
1065 }
1066 EXPORT_SYMBOL_GPL(zs_map_object);
1067 
1068 void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
1069 {
1070         struct page *page;
1071         unsigned long obj_idx, off;
1072 
1073         unsigned int class_idx;
1074         enum fullness_group fg;
1075         struct size_class *class;
1076         struct mapping_area *area;
1077 
1078         BUG_ON(!handle);
1079 
1080         obj_handle_to_location(handle, &page, &obj_idx);
1081         get_zspage_mapping(get_first_page(page), &class_idx, &fg);
1082         class = &pool->size_class[class_idx];
1083         off = obj_idx_to_offset(page, obj_idx, class->size);
1084 
1085         area = &__get_cpu_var(zs_map_area);
1086         if (off + class->size <= PAGE_SIZE)
1087                 kunmap_atomic(area->vm_addr);
1088         else {
1089                 struct page *pages[2];
1090 
1091                 pages[0] = page;
1092                 pages[1] = get_next_page(page);
1093                 BUG_ON(!pages[1]);
1094 
1095                 __zs_unmap_object(area, pages, off, class->size);
1096         }
1097         put_cpu_var(zs_map_area);
1098 }
1099 EXPORT_SYMBOL_GPL(zs_unmap_object);
1100 
1101 u64 zs_get_total_size_bytes(struct zs_pool *pool)
1102 {
1103         int i;
1104         u64 npages = 0;
1105 
1106         for (i = 0; i < ZS_SIZE_CLASSES; i++)
1107                 npages += pool->size_class[i].pages_allocated;
1108 
1109         return npages << PAGE_SHIFT;
1110 }
1111 EXPORT_SYMBOL_GPL(zs_get_total_size_bytes);
1112 
1113 module_init(zs_init);
1114 module_exit(zs_exit);
1115 
1116 MODULE_LICENSE("Dual BSD/GPL");
1117 MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");
1118 

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