cregit-Linux how code gets into the kernel

Release 4.7 mm/z3fold.c

Directory: mm
/*
 * z3fold.c
 *
 * Author: Vitaly Wool <vitaly.wool@konsulko.com>
 * Copyright (C) 2016, Sony Mobile Communications Inc.
 *
 * This implementation is based on zbud written by Seth Jennings.
 *
 * z3fold is an special purpose allocator for storing compressed pages. It
 * can store up to three compressed pages per page which improves the
 * compression ratio of zbud while retaining its main concepts (e. g. always
 * storing an integral number of objects per page) and simplicity.
 * It still has simple and deterministic reclaim properties that make it
 * preferable to a higher density approach (with no requirement on integral
 * number of object per page) when reclaim is used.
 *
 * As in zbud, pages are divided into "chunks".  The size of the chunks is
 * fixed at compile time and is determined by NCHUNKS_ORDER below.
 *
 * z3fold doesn't export any API and is meant to be used via zpool API.
 */


#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/atomic.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/preempt.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/zpool.h>

/*****************
 * Structures
*****************/
/*
 * NCHUNKS_ORDER determines the internal allocation granularity, effectively
 * adjusting internal fragmentation.  It also determines the number of
 * freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the
 * allocation granularity will be in chunks of size PAGE_SIZE/64. As one chunk
 * in allocated page is occupied by z3fold header, NCHUNKS will be calculated
 * to 63 which shows the max number of free chunks in z3fold page, also there
 * will be 63 freelists per pool.
 */

#define NCHUNKS_ORDER	6


#define CHUNK_SHIFT	(PAGE_SHIFT - NCHUNKS_ORDER)

#define CHUNK_SIZE	(1 << CHUNK_SHIFT)

#define ZHDR_SIZE_ALIGNED CHUNK_SIZE

#define NCHUNKS		((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT)


#define BUDDY_MASK	((1 << NCHUNKS_ORDER) - 1)

struct z3fold_pool;

struct z3fold_ops {
	
int (*evict)(struct z3fold_pool *pool, unsigned long handle);
};

/**
 * struct z3fold_pool - stores metadata for each z3fold pool
 * @lock:       protects all pool fields and first|last_chunk fields of any
 *              z3fold page in the pool
 * @unbuddied:  array of lists tracking z3fold pages that contain 2- buddies;
 *              the lists each z3fold page is added to depends on the size of
 *              its free region.
 * @buddied:    list tracking the z3fold pages that contain 3 buddies;
 *              these z3fold pages are full
 * @lru:        list tracking the z3fold pages in LRU order by most recently
 *              added buddy.
 * @pages_nr:   number of z3fold pages in the pool.
 * @ops:        pointer to a structure of user defined operations specified at
 *              pool creation time.
 *
 * This structure is allocated at pool creation time and maintains metadata
 * pertaining to a particular z3fold pool.
 */

struct z3fold_pool {
	
spinlock_t lock;
	
struct list_head unbuddied[NCHUNKS];
	
struct list_head buddied;
	
struct list_head lru;
	
u64 pages_nr;
	
const struct z3fold_ops *ops;
	
struct zpool *zpool;
	
const struct zpool_ops *zpool_ops;
};


enum buddy {
	
HEADLESS = 0,
	
FIRST,
	
MIDDLE,
	
LAST,
	
BUDDIES_MAX
};

/*
 * struct z3fold_header - z3fold page metadata occupying the first chunk of each
 *                      z3fold page, except for HEADLESS pages
 * @buddy:      links the z3fold page into the relevant list in the pool
 * @first_chunks:       the size of the first buddy in chunks, 0 if free
 * @middle_chunks:      the size of the middle buddy in chunks, 0 if free
 * @last_chunks:        the size of the last buddy in chunks, 0 if free
 * @first_num:          the starting number (for the first handle)
 */

struct z3fold_header {
	
struct list_head buddy;
	
unsigned short first_chunks;
	
unsigned short middle_chunks;
	
unsigned short last_chunks;
	
unsigned short start_middle;
	
unsigned short first_num:NCHUNKS_ORDER;
};

/*
 * Internal z3fold page flags
 */

enum z3fold_page_flags {
	
UNDER_RECLAIM = 0,
	
PAGE_HEADLESS,
	
MIDDLE_CHUNK_MAPPED,
};

/*****************
 * Helpers
*****************/

/* Converts an allocation size in bytes to size in z3fold chunks */

static int size_to_chunks(size_t size) { return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT; }

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#define for_each_unbuddied_list(_iter, _begin) \ for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++) /* Initializes the z3fold header of a newly allocated z3fold page */
static struct z3fold_header *init_z3fold_page(struct page *page) { struct z3fold_header *zhdr = page_address(page); INIT_LIST_HEAD(&page->lru); clear_bit(UNDER_RECLAIM, &page->private); clear_bit(PAGE_HEADLESS, &page->private); clear_bit(MIDDLE_CHUNK_MAPPED, &page->private); zhdr->first_chunks = 0; zhdr->middle_chunks = 0; zhdr->last_chunks = 0; zhdr->first_num = 0; zhdr->start_middle = 0; INIT_LIST_HEAD(&zhdr->buddy); return zhdr; }

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/* Resets the struct page fields and frees the page */
static void free_z3fold_page(struct z3fold_header *zhdr) { __free_page(virt_to_page(zhdr)); }

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/* * Encodes the handle of a particular buddy within a z3fold page * Pool lock should be held as this function accesses first_num */
static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud) { unsigned long handle; handle = (unsigned long)zhdr; if (bud != HEADLESS) handle += (bud + zhdr->first_num) & BUDDY_MASK; return handle; }

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/* Returns the z3fold page where a given handle is stored */
static struct z3fold_header *handle_to_z3fold_header(unsigned long handle) { return (struct z3fold_header *)(handle & PAGE_MASK); }

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/* Returns buddy number */
static enum buddy handle_to_buddy(unsigned long handle) { struct z3fold_header *zhdr = handle_to_z3fold_header(handle); return (handle - zhdr->first_num) & BUDDY_MASK; }

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/* * Returns the number of free chunks in a z3fold page. * NB: can't be used with HEADLESS pages. */
static int num_free_chunks(struct z3fold_header *zhdr) { int nfree; /* * If there is a middle object, pick up the bigger free space * either before or after it. Otherwise just subtract the number * of chunks occupied by the first and the last objects. */ if (zhdr->middle_chunks != 0) { int nfree_before = zhdr->first_chunks ? 0 : zhdr->start_middle - 1; int nfree_after = zhdr->last_chunks ? 0 : NCHUNKS - zhdr->start_middle - zhdr->middle_chunks; nfree = max(nfree_before, nfree_after); } else nfree = NCHUNKS - zhdr->first_chunks - zhdr->last_chunks; return nfree; }

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/***************** * API Functions *****************/ /** * z3fold_create_pool() - create a new z3fold pool * @gfp: gfp flags when allocating the z3fold pool structure * @ops: user-defined operations for the z3fold pool * * Return: pointer to the new z3fold pool or NULL if the metadata allocation * failed. */
static struct z3fold_pool *z3fold_create_pool(gfp_t gfp, const struct z3fold_ops *ops) { struct z3fold_pool *pool; int i; pool = kzalloc(sizeof(struct z3fold_pool), gfp); if (!pool) return NULL; spin_lock_init(&pool->lock); for_each_unbuddied_list(i, 0) INIT_LIST_HEAD(&pool->unbuddied[i]); INIT_LIST_HEAD(&pool->buddied); INIT_LIST_HEAD(&pool->lru); pool->pages_nr = 0; pool->ops = ops; return pool; }

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/** * z3fold_destroy_pool() - destroys an existing z3fold pool * @pool: the z3fold pool to be destroyed * * The pool should be emptied before this function is called. */
static void z3fold_destroy_pool(struct z3fold_pool *pool) { kfree(pool); }

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/* Has to be called with lock held */
static int z3fold_compact_page(struct z3fold_header *zhdr) { struct page *page = virt_to_page(zhdr); void *beg = zhdr; if (!test_bit(MIDDLE_CHUNK_MAPPED, &page->private) && zhdr->middle_chunks != 0 && zhdr->first_chunks == 0 && zhdr->last_chunks == 0) { memmove(beg + ZHDR_SIZE_ALIGNED, beg + (zhdr->start_middle << CHUNK_SHIFT), zhdr->middle_chunks << CHUNK_SHIFT); zhdr->first_chunks = zhdr->middle_chunks; zhdr->middle_chunks = 0; zhdr->start_middle = 0; zhdr->first_num++; return 1; } return 0; }

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/** * z3fold_alloc() - allocates a region of a given size * @pool: z3fold pool from which to allocate * @size: size in bytes of the desired allocation * @gfp: gfp flags used if the pool needs to grow * @handle: handle of the new allocation * * This function will attempt to find a free region in the pool large enough to * satisfy the allocation request. A search of the unbuddied lists is * performed first. If no suitable free region is found, then a new page is * allocated and added to the pool to satisfy the request. * * gfp should not set __GFP_HIGHMEM as highmem pages cannot be used * as z3fold pool pages. * * Return: 0 if success and handle is set, otherwise -EINVAL if the size or * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate * a new page. */
static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp, unsigned long *handle) { int chunks = 0, i, freechunks; struct z3fold_header *zhdr = NULL; enum buddy bud; struct page *page; if (!size || (gfp & __GFP_HIGHMEM)) return -EINVAL; if (size > PAGE_SIZE) return -ENOSPC; if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE) bud = HEADLESS; else { chunks = size_to_chunks(size); spin_lock(&pool->lock); /* First, try to find an unbuddied z3fold page. */ zhdr = NULL; for_each_unbuddied_list(i, chunks) { if (!list_empty(&pool->unbuddied[i])) { zhdr = list_first_entry(&pool->unbuddied[i], struct z3fold_header, buddy); page = virt_to_page(zhdr); if (zhdr->first_chunks == 0) { if (zhdr->middle_chunks != 0 && chunks >= zhdr->start_middle) bud = LAST; else bud = FIRST; } else if (zhdr->last_chunks == 0) bud = LAST; else if (zhdr->middle_chunks == 0) bud = MIDDLE; else { pr_err("No free chunks in unbuddied\n"); WARN_ON(1); continue; } list_del(&zhdr->buddy); goto found; } } bud = FIRST; spin_unlock(&pool->lock); } /* Couldn't find unbuddied z3fold page, create new one */ page = alloc_page(gfp); if (!page) return -ENOMEM; spin_lock(&pool->lock); pool->pages_nr++; zhdr = init_z3fold_page(page); if (bud == HEADLESS) { set_bit(PAGE_HEADLESS, &page->private); goto headless; } found: if (bud == FIRST) zhdr->first_chunks = chunks; else if (bud == LAST) zhdr->last_chunks = chunks; else { zhdr->middle_chunks = chunks; zhdr->start_middle = zhdr->first_chunks + 1; } if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 || zhdr->middle_chunks == 0) { /* Add to unbuddied list */ freechunks = num_free_chunks(zhdr); list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); } else { /* Add to buddied list */ list_add(&zhdr->buddy, &pool->buddied); } headless: /* Add/move z3fold page to beginning of LRU */ if (!list_empty(&page->lru)) list_del(&page->lru); list_add(&page->lru, &pool->lru); *handle = encode_handle(zhdr, bud); spin_unlock(&pool->lock); return 0; }

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/** * z3fold_free() - frees the allocation associated with the given handle * @pool: pool in which the allocation resided * @handle: handle associated with the allocation returned by z3fold_alloc() * * In the case that the z3fold page in which the allocation resides is under * reclaim, as indicated by the PG_reclaim flag being set, this function * only sets the first|last_chunks to 0. The page is actually freed * once both buddies are evicted (see z3fold_reclaim_page() below). */
static void z3fold_free(struct z3fold_pool *pool, unsigned long handle) { struct z3fold_header *zhdr; int freechunks; struct page *page; enum buddy bud; spin_lock(&pool->lock); zhdr = handle_to_z3fold_header(handle); page = virt_to_page(zhdr); if (test_bit(PAGE_HEADLESS, &page->private)) { /* HEADLESS page stored */ bud = HEADLESS; } else { bud = handle_to_buddy(handle); switch (bud) { case FIRST: zhdr->first_chunks = 0; break; case MIDDLE: zhdr->middle_chunks = 0; zhdr->start_middle = 0; break; case LAST: zhdr->last_chunks = 0; break; default: pr_err("%s: unknown bud %d\n", __func__, bud); WARN_ON(1); spin_unlock(&pool->lock); return; } } if (test_bit(UNDER_RECLAIM, &page->private)) { /* z3fold page is under reclaim, reclaim will free */ spin_unlock(&pool->lock); return; } if (bud != HEADLESS) { /* Remove from existing buddy list */ list_del(&zhdr->buddy); } if (bud == HEADLESS || (zhdr->first_chunks == 0 && zhdr->middle_chunks == 0 && zhdr->last_chunks == 0)) { /* z3fold page is empty, free */ list_del(&page->lru); clear_bit(PAGE_HEADLESS, &page->private); free_z3fold_page(zhdr); pool->pages_nr--; } else { z3fold_compact_page(zhdr); /* Add to the unbuddied list */ freechunks = num_free_chunks(zhdr); list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); } spin_unlock(&pool->lock); }

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/** * z3fold_reclaim_page() - evicts allocations from a pool page and frees it * @pool: pool from which a page will attempt to be evicted * @retires: number of pages on the LRU list for which eviction will * be attempted before failing * * z3fold reclaim is different from normal system reclaim in that it is done * from the bottom, up. This is because only the bottom layer, z3fold, has * information on how the allocations are organized within each z3fold page. * This has the potential to create interesting locking situations between * z3fold and the user, however. * * To avoid these, this is how z3fold_reclaim_page() should be called: * The user detects a page should be reclaimed and calls z3fold_reclaim_page(). * z3fold_reclaim_page() will remove a z3fold page from the pool LRU list and * call the user-defined eviction handler with the pool and handle as * arguments. * * If the handle can not be evicted, the eviction handler should return * non-zero. z3fold_reclaim_page() will add the z3fold page back to the * appropriate list and try the next z3fold page on the LRU up to * a user defined number of retries. * * If the handle is successfully evicted, the eviction handler should * return 0 _and_ should have called z3fold_free() on the handle. z3fold_free() * contains logic to delay freeing the page if the page is under reclaim, * as indicated by the setting of the PG_reclaim flag on the underlying page. * * If all buddies in the z3fold page are successfully evicted, then the * z3fold page can be freed. * * Returns: 0 if page is successfully freed, otherwise -EINVAL if there are * no pages to evict or an eviction handler is not registered, -EAGAIN if * the retry limit was hit. */
static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) { int i, ret = 0, freechunks; struct z3fold_header *zhdr; struct page *page; unsigned long first_handle = 0, middle_handle = 0, last_handle = 0; spin_lock(&pool->lock); if (!pool->ops || !pool->ops->evict || list_empty(&pool->lru) || retries == 0) { spin_unlock(&pool->lock); return -EINVAL; } for (i = 0; i < retries; i++) { page = list_last_entry(&pool->lru, struct page, lru); list_del(&page->lru); /* Protect z3fold page against free */ set_bit(UNDER_RECLAIM, &page->private); zhdr = page_address(page); if (!test_bit(PAGE_HEADLESS, &page->private)) { list_del(&zhdr->buddy); /* * We need encode the handles before unlocking, since * we can race with free that will set * (first|last)_chunks to 0 */ first_handle = 0; last_handle = 0; middle_handle = 0; if (zhdr->first_chunks) first_handle = encode_handle(zhdr, FIRST); if (zhdr->middle_chunks) middle_handle = encode_handle(zhdr, MIDDLE); if (zhdr->last_chunks) last_handle = encode_handle(zhdr, LAST); } else { first_handle = encode_handle(zhdr, HEADLESS); last_handle = middle_handle = 0; } spin_unlock(&pool->lock); /* Issue the eviction callback(s) */ if (middle_handle) { ret = pool->ops->evict(pool, middle_handle); if (ret) goto next; } if (first_handle) { ret = pool->ops->evict(pool, first_handle); if (ret) goto next; } if (last_handle) { ret = pool->ops->evict(pool, last_handle); if (ret) goto next; } next: spin_lock(&pool->lock); clear_bit(UNDER_RECLAIM, &page->private); if ((test_bit(PAGE_HEADLESS, &page->private) && ret == 0) || (zhdr->first_chunks == 0 && zhdr->last_chunks == 0 && zhdr->middle_chunks == 0)) { /* * All buddies are now free, free the z3fold page and * return success. */ clear_bit(PAGE_HEADLESS, &page->private); free_z3fold_page(zhdr); pool->pages_nr--; spin_unlock(&pool->lock); return 0; } else if (!test_bit(PAGE_HEADLESS, &page->private)) { if (zhdr->first_chunks != 0 && zhdr->last_chunks != 0 && zhdr->middle_chunks != 0) { /* Full, add to buddied list */ list_add(&zhdr->buddy, &pool->buddied); } else { z3fold_compact_page(zhdr); /* add to unbuddied list */ freechunks = num_free_chunks(zhdr); list_add(&zhdr->buddy, &pool->unbuddied[freechunks]); } } /* add to beginning of LRU */ list_add(&page->lru, &pool->lru); } spin_unlock(&pool->lock); return -EAGAIN; }

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/** * z3fold_map() - maps the allocation associated with the given handle * @pool: pool in which the allocation resides * @handle: handle associated with the allocation to be mapped * * Extracts the buddy number from handle and constructs the pointer to the * correct starting chunk within the page. * * Returns: a pointer to the mapped allocation */
static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle) { struct z3fold_header *zhdr; struct page *page; void *addr; enum buddy buddy; spin_lock(&pool->lock); zhdr = handle_to_z3fold_header(handle); addr = zhdr; page = virt_to_page(zhdr); if (test_bit(PAGE_HEADLESS, &page->private)) goto out; buddy = handle_to_buddy(handle); switch (buddy) { case FIRST: addr += ZHDR_SIZE_ALIGNED; break; case MIDDLE: addr += zhdr->start_middle << CHUNK_SHIFT; set_bit(MIDDLE_CHUNK_MAPPED, &page->private); break; case LAST: addr += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT); break; default: pr_err("unknown buddy id %d\n", buddy); WARN_ON(1); addr = NULL; break; } out: spin_unlock(&pool->lock); return addr; }

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/** * z3fold_unmap() - unmaps the allocation associated with the given handle * @pool: pool in which the allocation resides * @handle: handle associated with the allocation to be unmapped */
static void z3fold_unmap(struct z3fold_pool *pool, unsigned long handle) { struct z3fold_header *zhdr; struct page *page; enum buddy buddy; spin_lock(&pool->lock); zhdr = handle_to_z3fold_header(handle); page = virt_to_page(zhdr); if (test_bit(PAGE_HEADLESS, &page->private)) { spin_unlock(&pool->lock); return; } buddy = handle_to_buddy(handle); if (buddy == MIDDLE) clear_bit(MIDDLE_CHUNK_MAPPED, &page->private); spin_unlock(&pool->lock); }

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/** * z3fold_get_pool_size() - gets the z3fold pool size in pages * @pool: pool whose size is being queried * * Returns: size in pages of the given pool. The pool lock need not be * taken to access pages_nr. */
static u64 z3fold_get_pool_size(struct z3fold_pool *pool) { return pool->pages_nr; }

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/***************** * zpool ****************/
static int z3fold_zpool_evict(struct z3fold_pool *pool, unsigned long handle) { if (pool->zpool && pool->zpool_ops && pool->zpool_ops->evict) return pool->zpool_ops->evict(pool->zpool, handle); else return -ENOENT; }

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static const struct z3fold_ops z3fold_zpool_ops = { .evict = z3fold_zpool_evict };
static void *z3fold_zpool_create(const char *name, gfp_t gfp, const struct zpool_ops *zpool_ops, struct zpool *zpool) { struct z3fold_pool *pool; pool = z3fold_create_pool(gfp, zpool_ops ? &z3fold_zpool_ops : NULL); if (pool) { pool->zpool = zpool; pool->zpool_ops = zpool_ops; } return pool; }

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static void z3fold_zpool_destroy(void *pool) { z3fold_destroy_pool(pool); }

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static int z3fold_zpool_malloc(void *pool, size_t size, gfp_t gfp, unsigned long *handle) { return z3fold_alloc(pool, size, gfp, handle); }

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static void z3fold_zpool_free(void *pool, unsigned long handle) { z3fold_free(pool, handle); }

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static int z3fold_zpool_shrink(void *pool, unsigned int pages, unsigned int *reclaimed) { unsigned int total = 0; int ret = -EINVAL; while (total < pages) { ret = z3fold_reclaim_page(pool, 8); if (ret < 0) break; total++; } if (reclaimed) *reclaimed = total; return ret; }

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static void *z3fold_zpool_map(void *pool, unsigned long handle, enum zpool_mapmode mm) { return z3fold_map(pool, handle); }

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static void z3fold_zpool_unmap(void *pool, unsigned long handle) { z3fold_unmap(pool, handle); }

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static u64 z3fold_zpool_total_size(void *pool) { return z3fold_get_pool_size(pool) * PAGE_SIZE; }

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static struct zpool_driver z3fold_zpool_driver = { .type = "z3fold", .owner = THIS_MODULE, .create = z3fold_zpool_create, .destroy = z3fold_zpool_destroy, .malloc = z3fold_zpool_malloc, .free = z3fold_zpool_free, .shrink = z3fold_zpool_shrink, .map = z3fold_zpool_map, .unmap = z3fold_zpool_unmap, .total_size = z3fold_zpool_total_size, }; MODULE_ALIAS("zpool-z3fold");
static int __init init_z3fold(void) { /* Make sure the z3fold header will fit in one chunk */ BUILD_BUG_ON(sizeof(struct z3fold_header) > ZHDR_SIZE_ALIGNED); zpool_register_driver(&z3fold_zpool_driver); return 0; }

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static void __exit exit_z3fold(void) { zpool_unregister_driver(&z3fold_zpool_driver); }

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module_init(init_z3fold); module_exit(exit_z3fold); MODULE_LICENSE("GPL"); MODULE_AUTHOR("Vitaly Wool <vitalywool@gmail.com>"); MODULE_DESCRIPTION("3-Fold Allocator for Compressed Pages");

Overall Contributors

PersonTokensPropCommitsCommitProp
vitaly woolvitaly wool2834100.00%2100.00%
Total2834100.00%2100.00%
Directory: mm
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