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TOMOYO Linux Cross Reference
Linux/mm/z3fold.c

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  1 /*
  2  * z3fold.c
  3  *
  4  * Author: Vitaly Wool <vitaly.wool@konsulko.com>
  5  * Copyright (C) 2016, Sony Mobile Communications Inc.
  6  *
  7  * This implementation is based on zbud written by Seth Jennings.
  8  *
  9  * z3fold is an special purpose allocator for storing compressed pages. It
 10  * can store up to three compressed pages per page which improves the
 11  * compression ratio of zbud while retaining its main concepts (e. g. always
 12  * storing an integral number of objects per page) and simplicity.
 13  * It still has simple and deterministic reclaim properties that make it
 14  * preferable to a higher density approach (with no requirement on integral
 15  * number of object per page) when reclaim is used.
 16  *
 17  * As in zbud, pages are divided into "chunks".  The size of the chunks is
 18  * fixed at compile time and is determined by NCHUNKS_ORDER below.
 19  *
 20  * z3fold doesn't export any API and is meant to be used via zpool API.
 21  */
 22 
 23 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 24 
 25 #include <linux/atomic.h>
 26 #include <linux/sched.h>
 27 #include <linux/list.h>
 28 #include <linux/mm.h>
 29 #include <linux/module.h>
 30 #include <linux/percpu.h>
 31 #include <linux/preempt.h>
 32 #include <linux/workqueue.h>
 33 #include <linux/slab.h>
 34 #include <linux/spinlock.h>
 35 #include <linux/zpool.h>
 36 
 37 /*****************
 38  * Structures
 39 *****************/
 40 struct z3fold_pool;
 41 struct z3fold_ops {
 42         int (*evict)(struct z3fold_pool *pool, unsigned long handle);
 43 };
 44 
 45 enum buddy {
 46         HEADLESS = 0,
 47         FIRST,
 48         MIDDLE,
 49         LAST,
 50         BUDDIES_MAX
 51 };
 52 
 53 /*
 54  * struct z3fold_header - z3fold page metadata occupying first chunks of each
 55  *                      z3fold page, except for HEADLESS pages
 56  * @buddy:              links the z3fold page into the relevant list in the
 57  *                      pool
 58  * @page_lock:          per-page lock
 59  * @refcount:           reference count for the z3fold page
 60  * @work:               work_struct for page layout optimization
 61  * @pool:               pointer to the pool which this page belongs to
 62  * @cpu:                CPU which this page "belongs" to
 63  * @first_chunks:       the size of the first buddy in chunks, 0 if free
 64  * @middle_chunks:      the size of the middle buddy in chunks, 0 if free
 65  * @last_chunks:        the size of the last buddy in chunks, 0 if free
 66  * @first_num:          the starting number (for the first handle)
 67  */
 68 struct z3fold_header {
 69         struct list_head buddy;
 70         spinlock_t page_lock;
 71         struct kref refcount;
 72         struct work_struct work;
 73         struct z3fold_pool *pool;
 74         short cpu;
 75         unsigned short first_chunks;
 76         unsigned short middle_chunks;
 77         unsigned short last_chunks;
 78         unsigned short start_middle;
 79         unsigned short first_num:2;
 80 };
 81 
 82 /*
 83  * NCHUNKS_ORDER determines the internal allocation granularity, effectively
 84  * adjusting internal fragmentation.  It also determines the number of
 85  * freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the
 86  * allocation granularity will be in chunks of size PAGE_SIZE/64. Some chunks
 87  * in the beginning of an allocated page are occupied by z3fold header, so
 88  * NCHUNKS will be calculated to 63 (or 62 in case CONFIG_DEBUG_SPINLOCK=y),
 89  * which shows the max number of free chunks in z3fold page, also there will
 90  * be 63, or 62, respectively, freelists per pool.
 91  */
 92 #define NCHUNKS_ORDER   6
 93 
 94 #define CHUNK_SHIFT     (PAGE_SHIFT - NCHUNKS_ORDER)
 95 #define CHUNK_SIZE      (1 << CHUNK_SHIFT)
 96 #define ZHDR_SIZE_ALIGNED round_up(sizeof(struct z3fold_header), CHUNK_SIZE)
 97 #define ZHDR_CHUNKS     (ZHDR_SIZE_ALIGNED >> CHUNK_SHIFT)
 98 #define TOTAL_CHUNKS    (PAGE_SIZE >> CHUNK_SHIFT)
 99 #define NCHUNKS         ((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT)
100 
101 #define BUDDY_MASK      (0x3)
102 
103 /**
104  * struct z3fold_pool - stores metadata for each z3fold pool
105  * @name:       pool name
106  * @lock:       protects pool unbuddied/lru lists
107  * @stale_lock: protects pool stale page list
108  * @unbuddied:  per-cpu array of lists tracking z3fold pages that contain 2-
109  *              buddies; the list each z3fold page is added to depends on
110  *              the size of its free region.
111  * @lru:        list tracking the z3fold pages in LRU order by most recently
112  *              added buddy.
113  * @stale:      list of pages marked for freeing
114  * @pages_nr:   number of z3fold pages in the pool.
115  * @ops:        pointer to a structure of user defined operations specified at
116  *              pool creation time.
117  * @compact_wq: workqueue for page layout background optimization
118  * @release_wq: workqueue for safe page release
119  * @work:       work_struct for safe page release
120  *
121  * This structure is allocated at pool creation time and maintains metadata
122  * pertaining to a particular z3fold pool.
123  */
124 struct z3fold_pool {
125         const char *name;
126         spinlock_t lock;
127         spinlock_t stale_lock;
128         struct list_head *unbuddied;
129         struct list_head lru;
130         struct list_head stale;
131         atomic64_t pages_nr;
132         const struct z3fold_ops *ops;
133         struct zpool *zpool;
134         const struct zpool_ops *zpool_ops;
135         struct workqueue_struct *compact_wq;
136         struct workqueue_struct *release_wq;
137         struct work_struct work;
138 };
139 
140 /*
141  * Internal z3fold page flags
142  */
143 enum z3fold_page_flags {
144         PAGE_HEADLESS = 0,
145         MIDDLE_CHUNK_MAPPED,
146         NEEDS_COMPACTING,
147         PAGE_STALE,
148         UNDER_RECLAIM
149 };
150 
151 /*****************
152  * Helpers
153 *****************/
154 
155 /* Converts an allocation size in bytes to size in z3fold chunks */
156 static int size_to_chunks(size_t size)
157 {
158         return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
159 }
160 
161 #define for_each_unbuddied_list(_iter, _begin) \
162         for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
163 
164 static void compact_page_work(struct work_struct *w);
165 
166 /* Initializes the z3fold header of a newly allocated z3fold page */
167 static struct z3fold_header *init_z3fold_page(struct page *page,
168                                         struct z3fold_pool *pool)
169 {
170         struct z3fold_header *zhdr = page_address(page);
171 
172         INIT_LIST_HEAD(&page->lru);
173         clear_bit(PAGE_HEADLESS, &page->private);
174         clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
175         clear_bit(NEEDS_COMPACTING, &page->private);
176         clear_bit(PAGE_STALE, &page->private);
177         clear_bit(UNDER_RECLAIM, &page->private);
178 
179         spin_lock_init(&zhdr->page_lock);
180         kref_init(&zhdr->refcount);
181         zhdr->first_chunks = 0;
182         zhdr->middle_chunks = 0;
183         zhdr->last_chunks = 0;
184         zhdr->first_num = 0;
185         zhdr->start_middle = 0;
186         zhdr->cpu = -1;
187         zhdr->pool = pool;
188         INIT_LIST_HEAD(&zhdr->buddy);
189         INIT_WORK(&zhdr->work, compact_page_work);
190         return zhdr;
191 }
192 
193 /* Resets the struct page fields and frees the page */
194 static void free_z3fold_page(struct page *page)
195 {
196         __free_page(page);
197 }
198 
199 /* Lock a z3fold page */
200 static inline void z3fold_page_lock(struct z3fold_header *zhdr)
201 {
202         spin_lock(&zhdr->page_lock);
203 }
204 
205 /* Try to lock a z3fold page */
206 static inline int z3fold_page_trylock(struct z3fold_header *zhdr)
207 {
208         return spin_trylock(&zhdr->page_lock);
209 }
210 
211 /* Unlock a z3fold page */
212 static inline void z3fold_page_unlock(struct z3fold_header *zhdr)
213 {
214         spin_unlock(&zhdr->page_lock);
215 }
216 
217 /*
218  * Encodes the handle of a particular buddy within a z3fold page
219  * Pool lock should be held as this function accesses first_num
220  */
221 static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
222 {
223         unsigned long handle;
224 
225         handle = (unsigned long)zhdr;
226         if (bud != HEADLESS)
227                 handle += (bud + zhdr->first_num) & BUDDY_MASK;
228         return handle;
229 }
230 
231 /* Returns the z3fold page where a given handle is stored */
232 static struct z3fold_header *handle_to_z3fold_header(unsigned long handle)
233 {
234         return (struct z3fold_header *)(handle & PAGE_MASK);
235 }
236 
237 /*
238  * (handle & BUDDY_MASK) < zhdr->first_num is possible in encode_handle
239  *  but that doesn't matter. because the masking will result in the
240  *  correct buddy number.
241  */
242 static enum buddy handle_to_buddy(unsigned long handle)
243 {
244         struct z3fold_header *zhdr = handle_to_z3fold_header(handle);
245         return (handle - zhdr->first_num) & BUDDY_MASK;
246 }
247 
248 static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
249 {
250         struct page *page = virt_to_page(zhdr);
251         struct z3fold_pool *pool = zhdr->pool;
252 
253         WARN_ON(!list_empty(&zhdr->buddy));
254         set_bit(PAGE_STALE, &page->private);
255         clear_bit(NEEDS_COMPACTING, &page->private);
256         spin_lock(&pool->lock);
257         if (!list_empty(&page->lru))
258                 list_del(&page->lru);
259         spin_unlock(&pool->lock);
260         if (locked)
261                 z3fold_page_unlock(zhdr);
262         spin_lock(&pool->stale_lock);
263         list_add(&zhdr->buddy, &pool->stale);
264         queue_work(pool->release_wq, &pool->work);
265         spin_unlock(&pool->stale_lock);
266 }
267 
268 static void __attribute__((__unused__))
269                         release_z3fold_page(struct kref *ref)
270 {
271         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
272                                                 refcount);
273         __release_z3fold_page(zhdr, false);
274 }
275 
276 static void release_z3fold_page_locked(struct kref *ref)
277 {
278         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
279                                                 refcount);
280         WARN_ON(z3fold_page_trylock(zhdr));
281         __release_z3fold_page(zhdr, true);
282 }
283 
284 static void release_z3fold_page_locked_list(struct kref *ref)
285 {
286         struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
287                                                refcount);
288         spin_lock(&zhdr->pool->lock);
289         list_del_init(&zhdr->buddy);
290         spin_unlock(&zhdr->pool->lock);
291 
292         WARN_ON(z3fold_page_trylock(zhdr));
293         __release_z3fold_page(zhdr, true);
294 }
295 
296 static void free_pages_work(struct work_struct *w)
297 {
298         struct z3fold_pool *pool = container_of(w, struct z3fold_pool, work);
299 
300         spin_lock(&pool->stale_lock);
301         while (!list_empty(&pool->stale)) {
302                 struct z3fold_header *zhdr = list_first_entry(&pool->stale,
303                                                 struct z3fold_header, buddy);
304                 struct page *page = virt_to_page(zhdr);
305 
306                 list_del(&zhdr->buddy);
307                 if (WARN_ON(!test_bit(PAGE_STALE, &page->private)))
308                         continue;
309                 spin_unlock(&pool->stale_lock);
310                 cancel_work_sync(&zhdr->work);
311                 free_z3fold_page(page);
312                 cond_resched();
313                 spin_lock(&pool->stale_lock);
314         }
315         spin_unlock(&pool->stale_lock);
316 }
317 
318 /*
319  * Returns the number of free chunks in a z3fold page.
320  * NB: can't be used with HEADLESS pages.
321  */
322 static int num_free_chunks(struct z3fold_header *zhdr)
323 {
324         int nfree;
325         /*
326          * If there is a middle object, pick up the bigger free space
327          * either before or after it. Otherwise just subtract the number
328          * of chunks occupied by the first and the last objects.
329          */
330         if (zhdr->middle_chunks != 0) {
331                 int nfree_before = zhdr->first_chunks ?
332                         0 : zhdr->start_middle - ZHDR_CHUNKS;
333                 int nfree_after = zhdr->last_chunks ?
334                         0 : TOTAL_CHUNKS -
335                                 (zhdr->start_middle + zhdr->middle_chunks);
336                 nfree = max(nfree_before, nfree_after);
337         } else
338                 nfree = NCHUNKS - zhdr->first_chunks - zhdr->last_chunks;
339         return nfree;
340 }
341 
342 static inline void *mchunk_memmove(struct z3fold_header *zhdr,
343                                 unsigned short dst_chunk)
344 {
345         void *beg = zhdr;
346         return memmove(beg + (dst_chunk << CHUNK_SHIFT),
347                        beg + (zhdr->start_middle << CHUNK_SHIFT),
348                        zhdr->middle_chunks << CHUNK_SHIFT);
349 }
350 
351 #define BIG_CHUNK_GAP   3
352 /* Has to be called with lock held */
353 static int z3fold_compact_page(struct z3fold_header *zhdr)
354 {
355         struct page *page = virt_to_page(zhdr);
356 
357         if (test_bit(MIDDLE_CHUNK_MAPPED, &page->private))
358                 return 0; /* can't move middle chunk, it's used */
359 
360         if (zhdr->middle_chunks == 0)
361                 return 0; /* nothing to compact */
362 
363         if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
364                 /* move to the beginning */
365                 mchunk_memmove(zhdr, ZHDR_CHUNKS);
366                 zhdr->first_chunks = zhdr->middle_chunks;
367                 zhdr->middle_chunks = 0;
368                 zhdr->start_middle = 0;
369                 zhdr->first_num++;
370                 return 1;
371         }
372 
373         /*
374          * moving data is expensive, so let's only do that if
375          * there's substantial gain (at least BIG_CHUNK_GAP chunks)
376          */
377         if (zhdr->first_chunks != 0 && zhdr->last_chunks == 0 &&
378             zhdr->start_middle - (zhdr->first_chunks + ZHDR_CHUNKS) >=
379                         BIG_CHUNK_GAP) {
380                 mchunk_memmove(zhdr, zhdr->first_chunks + ZHDR_CHUNKS);
381                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
382                 return 1;
383         } else if (zhdr->last_chunks != 0 && zhdr->first_chunks == 0 &&
384                    TOTAL_CHUNKS - (zhdr->last_chunks + zhdr->start_middle
385                                         + zhdr->middle_chunks) >=
386                         BIG_CHUNK_GAP) {
387                 unsigned short new_start = TOTAL_CHUNKS - zhdr->last_chunks -
388                         zhdr->middle_chunks;
389                 mchunk_memmove(zhdr, new_start);
390                 zhdr->start_middle = new_start;
391                 return 1;
392         }
393 
394         return 0;
395 }
396 
397 static void do_compact_page(struct z3fold_header *zhdr, bool locked)
398 {
399         struct z3fold_pool *pool = zhdr->pool;
400         struct page *page;
401         struct list_head *unbuddied;
402         int fchunks;
403 
404         page = virt_to_page(zhdr);
405         if (locked)
406                 WARN_ON(z3fold_page_trylock(zhdr));
407         else
408                 z3fold_page_lock(zhdr);
409         if (WARN_ON(!test_and_clear_bit(NEEDS_COMPACTING, &page->private))) {
410                 z3fold_page_unlock(zhdr);
411                 return;
412         }
413         spin_lock(&pool->lock);
414         list_del_init(&zhdr->buddy);
415         spin_unlock(&pool->lock);
416 
417         if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
418                 atomic64_dec(&pool->pages_nr);
419                 return;
420         }
421 
422         z3fold_compact_page(zhdr);
423         unbuddied = get_cpu_ptr(pool->unbuddied);
424         fchunks = num_free_chunks(zhdr);
425         if (fchunks < NCHUNKS &&
426             (!zhdr->first_chunks || !zhdr->middle_chunks ||
427                         !zhdr->last_chunks)) {
428                 /* the page's not completely free and it's unbuddied */
429                 spin_lock(&pool->lock);
430                 list_add(&zhdr->buddy, &unbuddied[fchunks]);
431                 spin_unlock(&pool->lock);
432                 zhdr->cpu = smp_processor_id();
433         }
434         put_cpu_ptr(pool->unbuddied);
435         z3fold_page_unlock(zhdr);
436 }
437 
438 static void compact_page_work(struct work_struct *w)
439 {
440         struct z3fold_header *zhdr = container_of(w, struct z3fold_header,
441                                                 work);
442 
443         do_compact_page(zhdr, false);
444 }
445 
446 
447 /*
448  * API Functions
449  */
450 
451 /**
452  * z3fold_create_pool() - create a new z3fold pool
453  * @name:       pool name
454  * @gfp:        gfp flags when allocating the z3fold pool structure
455  * @ops:        user-defined operations for the z3fold pool
456  *
457  * Return: pointer to the new z3fold pool or NULL if the metadata allocation
458  * failed.
459  */
460 static struct z3fold_pool *z3fold_create_pool(const char *name, gfp_t gfp,
461                 const struct z3fold_ops *ops)
462 {
463         struct z3fold_pool *pool = NULL;
464         int i, cpu;
465 
466         pool = kzalloc(sizeof(struct z3fold_pool), gfp);
467         if (!pool)
468                 goto out;
469         spin_lock_init(&pool->lock);
470         spin_lock_init(&pool->stale_lock);
471         pool->unbuddied = __alloc_percpu(sizeof(struct list_head)*NCHUNKS, 2);
472         if (!pool->unbuddied)
473                 goto out_pool;
474         for_each_possible_cpu(cpu) {
475                 struct list_head *unbuddied =
476                                 per_cpu_ptr(pool->unbuddied, cpu);
477                 for_each_unbuddied_list(i, 0)
478                         INIT_LIST_HEAD(&unbuddied[i]);
479         }
480         INIT_LIST_HEAD(&pool->lru);
481         INIT_LIST_HEAD(&pool->stale);
482         atomic64_set(&pool->pages_nr, 0);
483         pool->name = name;
484         pool->compact_wq = create_singlethread_workqueue(pool->name);
485         if (!pool->compact_wq)
486                 goto out_unbuddied;
487         pool->release_wq = create_singlethread_workqueue(pool->name);
488         if (!pool->release_wq)
489                 goto out_wq;
490         INIT_WORK(&pool->work, free_pages_work);
491         pool->ops = ops;
492         return pool;
493 
494 out_wq:
495         destroy_workqueue(pool->compact_wq);
496 out_unbuddied:
497         free_percpu(pool->unbuddied);
498 out_pool:
499         kfree(pool);
500 out:
501         return NULL;
502 }
503 
504 /**
505  * z3fold_destroy_pool() - destroys an existing z3fold pool
506  * @pool:       the z3fold pool to be destroyed
507  *
508  * The pool should be emptied before this function is called.
509  */
510 static void z3fold_destroy_pool(struct z3fold_pool *pool)
511 {
512         destroy_workqueue(pool->release_wq);
513         destroy_workqueue(pool->compact_wq);
514         kfree(pool);
515 }
516 
517 /**
518  * z3fold_alloc() - allocates a region of a given size
519  * @pool:       z3fold pool from which to allocate
520  * @size:       size in bytes of the desired allocation
521  * @gfp:        gfp flags used if the pool needs to grow
522  * @handle:     handle of the new allocation
523  *
524  * This function will attempt to find a free region in the pool large enough to
525  * satisfy the allocation request.  A search of the unbuddied lists is
526  * performed first. If no suitable free region is found, then a new page is
527  * allocated and added to the pool to satisfy the request.
528  *
529  * gfp should not set __GFP_HIGHMEM as highmem pages cannot be used
530  * as z3fold pool pages.
531  *
532  * Return: 0 if success and handle is set, otherwise -EINVAL if the size or
533  * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
534  * a new page.
535  */
536 static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
537                         unsigned long *handle)
538 {
539         int chunks = 0, i, freechunks;
540         struct z3fold_header *zhdr = NULL;
541         struct page *page = NULL;
542         enum buddy bud;
543         bool can_sleep = gfpflags_allow_blocking(gfp);
544 
545         if (!size || (gfp & __GFP_HIGHMEM))
546                 return -EINVAL;
547 
548         if (size > PAGE_SIZE)
549                 return -ENOSPC;
550 
551         if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
552                 bud = HEADLESS;
553         else {
554                 struct list_head *unbuddied;
555                 chunks = size_to_chunks(size);
556 
557 lookup:
558                 /* First, try to find an unbuddied z3fold page. */
559                 unbuddied = get_cpu_ptr(pool->unbuddied);
560                 for_each_unbuddied_list(i, chunks) {
561                         struct list_head *l = &unbuddied[i];
562 
563                         zhdr = list_first_entry_or_null(READ_ONCE(l),
564                                                 struct z3fold_header, buddy);
565 
566                         if (!zhdr)
567                                 continue;
568 
569                         /* Re-check under lock. */
570                         spin_lock(&pool->lock);
571                         l = &unbuddied[i];
572                         if (unlikely(zhdr != list_first_entry(READ_ONCE(l),
573                                         struct z3fold_header, buddy)) ||
574                             !z3fold_page_trylock(zhdr)) {
575                                 spin_unlock(&pool->lock);
576                                 put_cpu_ptr(pool->unbuddied);
577                                 goto lookup;
578                         }
579                         list_del_init(&zhdr->buddy);
580                         zhdr->cpu = -1;
581                         spin_unlock(&pool->lock);
582 
583                         page = virt_to_page(zhdr);
584                         if (test_bit(NEEDS_COMPACTING, &page->private)) {
585                                 z3fold_page_unlock(zhdr);
586                                 zhdr = NULL;
587                                 put_cpu_ptr(pool->unbuddied);
588                                 if (can_sleep)
589                                         cond_resched();
590                                 goto lookup;
591                         }
592 
593                         /*
594                          * this page could not be removed from its unbuddied
595                          * list while pool lock was held, and then we've taken
596                          * page lock so kref_put could not be called before
597                          * we got here, so it's safe to just call kref_get()
598                          */
599                         kref_get(&zhdr->refcount);
600                         break;
601                 }
602                 put_cpu_ptr(pool->unbuddied);
603 
604                 if (zhdr) {
605                         if (zhdr->first_chunks == 0) {
606                                 if (zhdr->middle_chunks != 0 &&
607                                     chunks >= zhdr->start_middle)
608                                         bud = LAST;
609                                 else
610                                         bud = FIRST;
611                         } else if (zhdr->last_chunks == 0)
612                                 bud = LAST;
613                         else if (zhdr->middle_chunks == 0)
614                                 bud = MIDDLE;
615                         else {
616                                 if (kref_put(&zhdr->refcount,
617                                              release_z3fold_page_locked))
618                                         atomic64_dec(&pool->pages_nr);
619                                 else
620                                         z3fold_page_unlock(zhdr);
621                                 pr_err("No free chunks in unbuddied\n");
622                                 WARN_ON(1);
623                                 goto lookup;
624                         }
625                         goto found;
626                 }
627                 bud = FIRST;
628         }
629 
630         page = NULL;
631         if (can_sleep) {
632                 spin_lock(&pool->stale_lock);
633                 zhdr = list_first_entry_or_null(&pool->stale,
634                                                 struct z3fold_header, buddy);
635                 /*
636                  * Before allocating a page, let's see if we can take one from
637                  * the stale pages list. cancel_work_sync() can sleep so we
638                  * limit this case to the contexts where we can sleep
639                  */
640                 if (zhdr) {
641                         list_del(&zhdr->buddy);
642                         spin_unlock(&pool->stale_lock);
643                         cancel_work_sync(&zhdr->work);
644                         page = virt_to_page(zhdr);
645                 } else {
646                         spin_unlock(&pool->stale_lock);
647                 }
648         }
649         if (!page)
650                 page = alloc_page(gfp);
651 
652         if (!page)
653                 return -ENOMEM;
654 
655         atomic64_inc(&pool->pages_nr);
656         zhdr = init_z3fold_page(page, pool);
657 
658         if (bud == HEADLESS) {
659                 set_bit(PAGE_HEADLESS, &page->private);
660                 goto headless;
661         }
662         z3fold_page_lock(zhdr);
663 
664 found:
665         if (bud == FIRST)
666                 zhdr->first_chunks = chunks;
667         else if (bud == LAST)
668                 zhdr->last_chunks = chunks;
669         else {
670                 zhdr->middle_chunks = chunks;
671                 zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
672         }
673 
674         if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||
675                         zhdr->middle_chunks == 0) {
676                 struct list_head *unbuddied = get_cpu_ptr(pool->unbuddied);
677 
678                 /* Add to unbuddied list */
679                 freechunks = num_free_chunks(zhdr);
680                 spin_lock(&pool->lock);
681                 list_add(&zhdr->buddy, &unbuddied[freechunks]);
682                 spin_unlock(&pool->lock);
683                 zhdr->cpu = smp_processor_id();
684                 put_cpu_ptr(pool->unbuddied);
685         }
686 
687 headless:
688         spin_lock(&pool->lock);
689         /* Add/move z3fold page to beginning of LRU */
690         if (!list_empty(&page->lru))
691                 list_del(&page->lru);
692 
693         list_add(&page->lru, &pool->lru);
694 
695         *handle = encode_handle(zhdr, bud);
696         spin_unlock(&pool->lock);
697         if (bud != HEADLESS)
698                 z3fold_page_unlock(zhdr);
699 
700         return 0;
701 }
702 
703 /**
704  * z3fold_free() - frees the allocation associated with the given handle
705  * @pool:       pool in which the allocation resided
706  * @handle:     handle associated with the allocation returned by z3fold_alloc()
707  *
708  * In the case that the z3fold page in which the allocation resides is under
709  * reclaim, as indicated by the PG_reclaim flag being set, this function
710  * only sets the first|last_chunks to 0.  The page is actually freed
711  * once both buddies are evicted (see z3fold_reclaim_page() below).
712  */
713 static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
714 {
715         struct z3fold_header *zhdr;
716         struct page *page;
717         enum buddy bud;
718 
719         zhdr = handle_to_z3fold_header(handle);
720         page = virt_to_page(zhdr);
721 
722         if (test_bit(PAGE_HEADLESS, &page->private)) {
723                 /* HEADLESS page stored */
724                 bud = HEADLESS;
725         } else {
726                 z3fold_page_lock(zhdr);
727                 bud = handle_to_buddy(handle);
728 
729                 switch (bud) {
730                 case FIRST:
731                         zhdr->first_chunks = 0;
732                         break;
733                 case MIDDLE:
734                         zhdr->middle_chunks = 0;
735                         zhdr->start_middle = 0;
736                         break;
737                 case LAST:
738                         zhdr->last_chunks = 0;
739                         break;
740                 default:
741                         pr_err("%s: unknown bud %d\n", __func__, bud);
742                         WARN_ON(1);
743                         z3fold_page_unlock(zhdr);
744                         return;
745                 }
746         }
747 
748         if (bud == HEADLESS) {
749                 spin_lock(&pool->lock);
750                 list_del(&page->lru);
751                 spin_unlock(&pool->lock);
752                 free_z3fold_page(page);
753                 atomic64_dec(&pool->pages_nr);
754                 return;
755         }
756 
757         if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list)) {
758                 atomic64_dec(&pool->pages_nr);
759                 return;
760         }
761         if (test_bit(UNDER_RECLAIM, &page->private)) {
762                 z3fold_page_unlock(zhdr);
763                 return;
764         }
765         if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
766                 z3fold_page_unlock(zhdr);
767                 return;
768         }
769         if (zhdr->cpu < 0 || !cpu_online(zhdr->cpu)) {
770                 spin_lock(&pool->lock);
771                 list_del_init(&zhdr->buddy);
772                 spin_unlock(&pool->lock);
773                 zhdr->cpu = -1;
774                 kref_get(&zhdr->refcount);
775                 do_compact_page(zhdr, true);
776                 return;
777         }
778         kref_get(&zhdr->refcount);
779         queue_work_on(zhdr->cpu, pool->compact_wq, &zhdr->work);
780         z3fold_page_unlock(zhdr);
781 }
782 
783 /**
784  * z3fold_reclaim_page() - evicts allocations from a pool page and frees it
785  * @pool:       pool from which a page will attempt to be evicted
786  * @retries:    number of pages on the LRU list for which eviction will
787  *              be attempted before failing
788  *
789  * z3fold reclaim is different from normal system reclaim in that it is done
790  * from the bottom, up. This is because only the bottom layer, z3fold, has
791  * information on how the allocations are organized within each z3fold page.
792  * This has the potential to create interesting locking situations between
793  * z3fold and the user, however.
794  *
795  * To avoid these, this is how z3fold_reclaim_page() should be called:
796  *
797  * The user detects a page should be reclaimed and calls z3fold_reclaim_page().
798  * z3fold_reclaim_page() will remove a z3fold page from the pool LRU list and
799  * call the user-defined eviction handler with the pool and handle as
800  * arguments.
801  *
802  * If the handle can not be evicted, the eviction handler should return
803  * non-zero. z3fold_reclaim_page() will add the z3fold page back to the
804  * appropriate list and try the next z3fold page on the LRU up to
805  * a user defined number of retries.
806  *
807  * If the handle is successfully evicted, the eviction handler should
808  * return 0 _and_ should have called z3fold_free() on the handle. z3fold_free()
809  * contains logic to delay freeing the page if the page is under reclaim,
810  * as indicated by the setting of the PG_reclaim flag on the underlying page.
811  *
812  * If all buddies in the z3fold page are successfully evicted, then the
813  * z3fold page can be freed.
814  *
815  * Returns: 0 if page is successfully freed, otherwise -EINVAL if there are
816  * no pages to evict or an eviction handler is not registered, -EAGAIN if
817  * the retry limit was hit.
818  */
819 static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
820 {
821         int i, ret = 0;
822         struct z3fold_header *zhdr = NULL;
823         struct page *page = NULL;
824         struct list_head *pos;
825         unsigned long first_handle = 0, middle_handle = 0, last_handle = 0;
826 
827         spin_lock(&pool->lock);
828         if (!pool->ops || !pool->ops->evict || retries == 0) {
829                 spin_unlock(&pool->lock);
830                 return -EINVAL;
831         }
832         for (i = 0; i < retries; i++) {
833                 if (list_empty(&pool->lru)) {
834                         spin_unlock(&pool->lock);
835                         return -EINVAL;
836                 }
837                 list_for_each_prev(pos, &pool->lru) {
838                         page = list_entry(pos, struct page, lru);
839                         if (test_bit(PAGE_HEADLESS, &page->private))
840                                 /* candidate found */
841                                 break;
842 
843                         zhdr = page_address(page);
844                         if (!z3fold_page_trylock(zhdr))
845                                 continue; /* can't evict at this point */
846                         kref_get(&zhdr->refcount);
847                         list_del_init(&zhdr->buddy);
848                         zhdr->cpu = -1;
849                         set_bit(UNDER_RECLAIM, &page->private);
850                         break;
851                 }
852 
853                 list_del_init(&page->lru);
854                 spin_unlock(&pool->lock);
855 
856                 if (!test_bit(PAGE_HEADLESS, &page->private)) {
857                         /*
858                          * We need encode the handles before unlocking, since
859                          * we can race with free that will set
860                          * (first|last)_chunks to 0
861                          */
862                         first_handle = 0;
863                         last_handle = 0;
864                         middle_handle = 0;
865                         if (zhdr->first_chunks)
866                                 first_handle = encode_handle(zhdr, FIRST);
867                         if (zhdr->middle_chunks)
868                                 middle_handle = encode_handle(zhdr, MIDDLE);
869                         if (zhdr->last_chunks)
870                                 last_handle = encode_handle(zhdr, LAST);
871                         /*
872                          * it's safe to unlock here because we hold a
873                          * reference to this page
874                          */
875                         z3fold_page_unlock(zhdr);
876                 } else {
877                         first_handle = encode_handle(zhdr, HEADLESS);
878                         last_handle = middle_handle = 0;
879                 }
880 
881                 /* Issue the eviction callback(s) */
882                 if (middle_handle) {
883                         ret = pool->ops->evict(pool, middle_handle);
884                         if (ret)
885                                 goto next;
886                 }
887                 if (first_handle) {
888                         ret = pool->ops->evict(pool, first_handle);
889                         if (ret)
890                                 goto next;
891                 }
892                 if (last_handle) {
893                         ret = pool->ops->evict(pool, last_handle);
894                         if (ret)
895                                 goto next;
896                 }
897 next:
898                 if (test_bit(PAGE_HEADLESS, &page->private)) {
899                         if (ret == 0) {
900                                 free_z3fold_page(page);
901                                 return 0;
902                         }
903                         spin_lock(&pool->lock);
904                         list_add(&page->lru, &pool->lru);
905                         spin_unlock(&pool->lock);
906                 } else {
907                         z3fold_page_lock(zhdr);
908                         clear_bit(UNDER_RECLAIM, &page->private);
909                         if (kref_put(&zhdr->refcount,
910                                         release_z3fold_page_locked)) {
911                                 atomic64_dec(&pool->pages_nr);
912                                 return 0;
913                         }
914                         /*
915                          * if we are here, the page is still not completely
916                          * free. Take the global pool lock then to be able
917                          * to add it back to the lru list
918                          */
919                         spin_lock(&pool->lock);
920                         list_add(&page->lru, &pool->lru);
921                         spin_unlock(&pool->lock);
922                         z3fold_page_unlock(zhdr);
923                 }
924 
925                 /* We started off locked to we need to lock the pool back */
926                 spin_lock(&pool->lock);
927         }
928         spin_unlock(&pool->lock);
929         return -EAGAIN;
930 }
931 
932 /**
933  * z3fold_map() - maps the allocation associated with the given handle
934  * @pool:       pool in which the allocation resides
935  * @handle:     handle associated with the allocation to be mapped
936  *
937  * Extracts the buddy number from handle and constructs the pointer to the
938  * correct starting chunk within the page.
939  *
940  * Returns: a pointer to the mapped allocation
941  */
942 static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
943 {
944         struct z3fold_header *zhdr;
945         struct page *page;
946         void *addr;
947         enum buddy buddy;
948 
949         zhdr = handle_to_z3fold_header(handle);
950         addr = zhdr;
951         page = virt_to_page(zhdr);
952 
953         if (test_bit(PAGE_HEADLESS, &page->private))
954                 goto out;
955 
956         z3fold_page_lock(zhdr);
957         buddy = handle_to_buddy(handle);
958         switch (buddy) {
959         case FIRST:
960                 addr += ZHDR_SIZE_ALIGNED;
961                 break;
962         case MIDDLE:
963                 addr += zhdr->start_middle << CHUNK_SHIFT;
964                 set_bit(MIDDLE_CHUNK_MAPPED, &page->private);
965                 break;
966         case LAST:
967                 addr += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
968                 break;
969         default:
970                 pr_err("unknown buddy id %d\n", buddy);
971                 WARN_ON(1);
972                 addr = NULL;
973                 break;
974         }
975 
976         z3fold_page_unlock(zhdr);
977 out:
978         return addr;
979 }
980 
981 /**
982  * z3fold_unmap() - unmaps the allocation associated with the given handle
983  * @pool:       pool in which the allocation resides
984  * @handle:     handle associated with the allocation to be unmapped
985  */
986 static void z3fold_unmap(struct z3fold_pool *pool, unsigned long handle)
987 {
988         struct z3fold_header *zhdr;
989         struct page *page;
990         enum buddy buddy;
991 
992         zhdr = handle_to_z3fold_header(handle);
993         page = virt_to_page(zhdr);
994 
995         if (test_bit(PAGE_HEADLESS, &page->private))
996                 return;
997 
998         z3fold_page_lock(zhdr);
999         buddy = handle_to_buddy(handle);
1000         if (buddy == MIDDLE)
1001                 clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
1002         z3fold_page_unlock(zhdr);
1003 }
1004 
1005 /**
1006  * z3fold_get_pool_size() - gets the z3fold pool size in pages
1007  * @pool:       pool whose size is being queried
1008  *
1009  * Returns: size in pages of the given pool.
1010  */
1011 static u64 z3fold_get_pool_size(struct z3fold_pool *pool)
1012 {
1013         return atomic64_read(&pool->pages_nr);
1014 }
1015 
1016 /*****************
1017  * zpool
1018  ****************/
1019 
1020 static int z3fold_zpool_evict(struct z3fold_pool *pool, unsigned long handle)
1021 {
1022         if (pool->zpool && pool->zpool_ops && pool->zpool_ops->evict)
1023                 return pool->zpool_ops->evict(pool->zpool, handle);
1024         else
1025                 return -ENOENT;
1026 }
1027 
1028 static const struct z3fold_ops z3fold_zpool_ops = {
1029         .evict =        z3fold_zpool_evict
1030 };
1031 
1032 static void *z3fold_zpool_create(const char *name, gfp_t gfp,
1033                                const struct zpool_ops *zpool_ops,
1034                                struct zpool *zpool)
1035 {
1036         struct z3fold_pool *pool;
1037 
1038         pool = z3fold_create_pool(name, gfp,
1039                                 zpool_ops ? &z3fold_zpool_ops : NULL);
1040         if (pool) {
1041                 pool->zpool = zpool;
1042                 pool->zpool_ops = zpool_ops;
1043         }
1044         return pool;
1045 }
1046 
1047 static void z3fold_zpool_destroy(void *pool)
1048 {
1049         z3fold_destroy_pool(pool);
1050 }
1051 
1052 static int z3fold_zpool_malloc(void *pool, size_t size, gfp_t gfp,
1053                         unsigned long *handle)
1054 {
1055         return z3fold_alloc(pool, size, gfp, handle);
1056 }
1057 static void z3fold_zpool_free(void *pool, unsigned long handle)
1058 {
1059         z3fold_free(pool, handle);
1060 }
1061 
1062 static int z3fold_zpool_shrink(void *pool, unsigned int pages,
1063                         unsigned int *reclaimed)
1064 {
1065         unsigned int total = 0;
1066         int ret = -EINVAL;
1067 
1068         while (total < pages) {
1069                 ret = z3fold_reclaim_page(pool, 8);
1070                 if (ret < 0)
1071                         break;
1072                 total++;
1073         }
1074 
1075         if (reclaimed)
1076                 *reclaimed = total;
1077 
1078         return ret;
1079 }
1080 
1081 static void *z3fold_zpool_map(void *pool, unsigned long handle,
1082                         enum zpool_mapmode mm)
1083 {
1084         return z3fold_map(pool, handle);
1085 }
1086 static void z3fold_zpool_unmap(void *pool, unsigned long handle)
1087 {
1088         z3fold_unmap(pool, handle);
1089 }
1090 
1091 static u64 z3fold_zpool_total_size(void *pool)
1092 {
1093         return z3fold_get_pool_size(pool) * PAGE_SIZE;
1094 }
1095 
1096 static struct zpool_driver z3fold_zpool_driver = {
1097         .type =         "z3fold",
1098         .owner =        THIS_MODULE,
1099         .create =       z3fold_zpool_create,
1100         .destroy =      z3fold_zpool_destroy,
1101         .malloc =       z3fold_zpool_malloc,
1102         .free =         z3fold_zpool_free,
1103         .shrink =       z3fold_zpool_shrink,
1104         .map =          z3fold_zpool_map,
1105         .unmap =        z3fold_zpool_unmap,
1106         .total_size =   z3fold_zpool_total_size,
1107 };
1108 
1109 MODULE_ALIAS("zpool-z3fold");
1110 
1111 static int __init init_z3fold(void)
1112 {
1113         /* Make sure the z3fold header is not larger than the page size */
1114         BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE);
1115         zpool_register_driver(&z3fold_zpool_driver);
1116 
1117         return 0;
1118 }
1119 
1120 static void __exit exit_z3fold(void)
1121 {
1122         zpool_unregister_driver(&z3fold_zpool_driver);
1123 }
1124 
1125 module_init(init_z3fold);
1126 module_exit(exit_z3fold);
1127 
1128 MODULE_LICENSE("GPL");
1129 MODULE_AUTHOR("Vitaly Wool <vitalywool@gmail.com>");
1130 MODULE_DESCRIPTION("3-Fold Allocator for Compressed Pages");
1131 

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