zbud: add to mm/

zbud is an special purpose allocator for storing compressed pages. It is designed to store up to two compressed pages per physical page. While this design limits storage density, it has simple and deterministic reclaim properties that make it preferable to a higher density approach when reclaim will be used. zbud works by storing compressed pages, or "zpages", together in pairs in a single memory page called a "zbud page". The first buddy is "left justifed" at the beginning of the zbud page, and the last buddy is "right justified" at the end of the zbud page. The benefit is that if either buddy is freed, the freed buddy space, coalesced with whatever slack space that existed between the buddies, results in the largest possible free region within the zbud page. zbud also provides an attractive lower bound on density. The ratio of zpages to zbud pages can not be less than 1. This ensures that zbud can never "do harm" by using more pages to store zpages than the uncompressed zpages would have used on their own. This implementation is a rewrite of the zbud allocator internally used by zcache in the driver/staging tree. The rewrite was necessary to remove some of the zcache specific elements that were ingrained throughout and provide a generic allocation interface that can later be used by zsmalloc and others. This patch adds zbud to mm/ for later use by zswap. Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com> Acked-by: Rik van Riel <riel@redhat.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Minchan Kim <minchan@kernel.org> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Dan Magenheimer <dan.magenheimer@oracle.com> Cc: Robert Jennings <rcj@linux.vnet.ibm.com> Cc: Jenifer Hopper <jhopper@us.ibm.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Johannes Weiner <jweiner@redhat.com> Cc: Larry Woodman <lwoodman@redhat.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Dave Hansen <dave@sr71.net> Cc: Joe Perches <joe@perches.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Cody P Schafer <cody@linux.vnet.ibm.com> Cc: Hugh Dickens <hughd@google.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Bob Liu <bob.liu@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

zbud: add to mm/
zbud is an special purpose allocator for storing compressed pages. It is designed to store up to two compressed pages per physical page. While this design limits storage density, it has simple and deterministic reclaim properties that make it preferable to a higher density approach when reclaim will be used. zbud works by storing compressed pages, or "zpages", together in pairs in a single memory page called a "zbud page". The first buddy is "left justifed" at the beginning of the zbud page, and the last buddy is "right justified" at the end of the zbud page. The benefit is that if either buddy is freed, the freed buddy space, coalesced with whatever slack space that existed between the buddies, results in the largest possible free region within the zbud page. zbud also provides an attractive lower bound on density. The ratio of zpages to zbud pages can not be less than 1. This ensures that zbud can never "do harm" by using more pages to store zpages than the uncompressed zpages would have used on their own. This implementation is a rewrite of the zbud allocator internally used by zcache in the driver/staging tree. The rewrite was necessary to remove some of the zcache specific elements that were ingrained throughout and provide a generic allocation interface that can later be used by zsmalloc and others. This patch adds zbud to mm/ for later use by zswap. Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com> Acked-by: Rik van Riel <riel@redhat.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Minchan Kim <minchan@kernel.org> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Dan Magenheimer <dan.magenheimer@oracle.com> Cc: Robert Jennings <rcj@linux.vnet.ibm.com> Cc: Jenifer Hopper <jhopper@us.ibm.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Johannes Weiner <jweiner@redhat.com> Cc: Larry Woodman <lwoodman@redhat.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Dave Hansen <dave@sr71.net> Cc: Joe Perches <joe@perches.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Cody P Schafer <cody@linux.vnet.ibm.com> Cc: Hugh Dickens <hughd@google.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Bob Liu <bob.liu@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Seth Jennings · Linus Torvalds
1 parent bfffbea1aa
Showing 4 changed files with 560 additions and 0 deletions Side-by-side Diff
include/linux/zbud.h
mm/Kconfig
mm/Makefile
mm/zbud.c
+#ifndef _ZBUD_H_
+#define _ZBUD_H_
+
+#include <linux/types.h>
+
+struct zbud_pool;
+
+struct zbud_ops {
+	int (*evict)(struct zbud_pool *pool, unsigned long handle);
+};
+
+struct zbud_pool *zbud_create_pool(gfp_t gfp, struct zbud_ops *ops);
+void zbud_destroy_pool(struct zbud_pool *pool);
+int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp,
+	unsigned long *handle);
+void zbud_free(struct zbud_pool *pool, unsigned long handle);
+int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries);
+void *zbud_map(struct zbud_pool *pool, unsigned long handle);
+void zbud_unmap(struct zbud_pool *pool, unsigned long handle);
+u64 zbud_get_pool_size(struct zbud_pool *pool);
+
+#endif /* _ZBUD_H_ */
@@ -478,6 +478,16 @@
  
 	  If unsure, say Y to enable frontswap.
  
+config ZBUD
+	tristate
+	default n
+	help
+	  A special purpose allocator for storing compressed pages.
+	  It is designed to store up to two compressed pages per physical
+	  page.  While this design limits storage density, it has simple and
+	  deterministic reclaim properties that make it preferable to a higher
+	  density approach when reclaim will be used.
+
 config MEM_SOFT_DIRTY
 	bool "Track memory changes"
 	depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY
@@ -58,4 +58,5 @@
 obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
 obj-$(CONFIG_CLEANCACHE) += cleancache.o
 obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
+obj-$(CONFIG_ZBUD)	+= zbud.o
+/*
+ * zbud.c
+ *
+ * Copyright (C) 2013, Seth Jennings, IBM
+ *
+ * Concepts based on zcache internal zbud allocator by Dan Magenheimer.
+ *
+ * zbud is an special purpose allocator for storing compressed pages.  Contrary
+ * to what its name may suggest, zbud is not a buddy allocator, but rather an
+ * allocator that "buddies" two compressed pages together in a single memory
+ * page.
+ *
+ * While this design limits storage density, it has simple and deterministic
+ * reclaim properties that make it preferable to a higher density approach when
+ * reclaim will be used.
+ *
+ * zbud works by storing compressed pages, or "zpages", together in pairs in a
+ * single memory page called a "zbud page".  The first buddy is "left
+ * justifed" at the beginning of the zbud page, and the last buddy is "right
+ * justified" at the end of the zbud page.  The benefit is that if either
+ * buddy is freed, the freed buddy space, coalesced with whatever slack space
+ * that existed between the buddies, results in the largest possible free region
+ * within the zbud page.
+ *
+ * zbud also provides an attractive lower bound on density. The ratio of zpages
+ * to zbud pages can not be less than 1.  This ensures that zbud can never "do
+ * harm" by using more pages to store zpages than the uncompressed zpages would
+ * have used on their own.
+ *
+ * zbud pages are divided into "chunks".  The size of the chunks is fixed at
+ * compile time and determined by NCHUNKS_ORDER below.  Dividing zbud pages
+ * into chunks allows organizing unbuddied zbud pages into a manageable number
+ * of unbuddied lists according to the number of free chunks available in the
+ * zbud page.
+ *
+ * The zbud API differs from that of conventional allocators in that the
+ * allocation function, zbud_alloc(), returns an opaque handle to the user,
+ * not a dereferenceable pointer.  The user must map the handle using
+ * zbud_map() in order to get a usable pointer by which to access the
+ * allocation data and unmap the handle with zbud_unmap() when operations
+ * on the allocation data are complete.
+ */
+
+#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/zbud.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, and there
+ * will be 64 freelists per pool.
+ */
+#define NCHUNKS_ORDER	6
+
+#define CHUNK_SHIFT	(PAGE_SHIFT - NCHUNKS_ORDER)
+#define CHUNK_SIZE	(1 << CHUNK_SHIFT)
+#define NCHUNKS		(PAGE_SIZE >> CHUNK_SHIFT)
+#define ZHDR_SIZE_ALIGNED CHUNK_SIZE
+
+/**
+ * struct zbud_pool - stores metadata for each zbud pool
+ * @lock:	protects all pool fields and first|last_chunk fields of any
+ *		zbud page in the pool
+ * @unbuddied:	array of lists tracking zbud pages that only contain one buddy;
+ *		the lists each zbud page is added to depends on the size of
+ *		its free region.
+ * @buddied:	list tracking the zbud pages that contain two buddies;
+ *		these zbud pages are full
+ * @lru:	list tracking the zbud pages in LRU order by most recently
+ *		added buddy.
+ * @pages_nr:	number of zbud 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 zbud pool.
+ */
+struct zbud_pool {
+	spinlock_t lock;
+	struct list_head unbuddied[NCHUNKS];
+	struct list_head buddied;
+	struct list_head lru;
+	u64 pages_nr;
+	struct zbud_ops *ops;
+};
+
+/*
+ * struct zbud_header - zbud page metadata occupying the first chunk of each
+ *			zbud page.
+ * @buddy:	links the zbud page into the unbuddied/buddied lists in the pool
+ * @lru:	links the zbud page into the lru list in the pool
+ * @first_chunks:	the size of the first buddy in chunks, 0 if free
+ * @last_chunks:	the size of the last buddy in chunks, 0 if free
+ */
+struct zbud_header {
+	struct list_head buddy;
+	struct list_head lru;
+	unsigned int first_chunks;
+	unsigned int last_chunks;
+	bool under_reclaim;
+};
+
+/*****************
+ * Helpers
+*****************/
+/* Just to make the code easier to read */
+enum buddy {
+	FIRST,
+	LAST
+};
+
+/* Converts an allocation size in bytes to size in zbud chunks */
+static int size_to_chunks(int size)
+{
+	return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
+}
+
+#define for_each_unbuddied_list(_iter, _begin) \
+	for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
+
+/* Initializes the zbud header of a newly allocated zbud page */
+static struct zbud_header *init_zbud_page(struct page *page)
+{
+	struct zbud_header *zhdr = page_address(page);
+	zhdr->first_chunks = 0;
+	zhdr->last_chunks = 0;
+	INIT_LIST_HEAD(&zhdr->buddy);
+	INIT_LIST_HEAD(&zhdr->lru);
+	zhdr->under_reclaim = 0;
+	return zhdr;
+}
+
+/* Resets the struct page fields and frees the page */
+static void free_zbud_page(struct zbud_header *zhdr)
+{
+	__free_page(virt_to_page(zhdr));
+}
+
+/*
+ * Encodes the handle of a particular buddy within a zbud page
+ * Pool lock should be held as this function accesses first|last_chunks
+ */
+static unsigned long encode_handle(struct zbud_header *zhdr, enum buddy bud)
+{
+	unsigned long handle;
+
+	/*
+	 * For now, the encoded handle is actually just the pointer to the data
+	 * but this might not always be the case.  A little information hiding.
+	 * Add CHUNK_SIZE to the handle if it is the first allocation to jump
+	 * over the zbud header in the first chunk.
+	 */
+	handle = (unsigned long)zhdr;
+	if (bud == FIRST)
+		/* skip over zbud header */
+		handle += ZHDR_SIZE_ALIGNED;
+	else /* bud == LAST */
+		handle += PAGE_SIZE - (zhdr->last_chunks  << CHUNK_SHIFT);
+	return handle;
+}
+
+/* Returns the zbud page where a given handle is stored */
+static struct zbud_header *handle_to_zbud_header(unsigned long handle)
+{
+	return (struct zbud_header *)(handle & PAGE_MASK);
+}
+
+/* Returns the number of free chunks in a zbud page */
+static int num_free_chunks(struct zbud_header *zhdr)
+{
+	/*
+	 * Rather than branch for different situations, just use the fact that
+	 * free buddies have a length of zero to simplify everything. -1 at the
+	 * end for the zbud header.
+	 */
+	return NCHUNKS - zhdr->first_chunks - zhdr->last_chunks - 1;
+}
+
+/*****************
+ * API Functions
+*****************/
+/**
+ * zbud_create_pool() - create a new zbud pool
+ * @gfp:	gfp flags when allocating the zbud pool structure
+ * @ops:	user-defined operations for the zbud pool
+ *
+ * Return: pointer to the new zbud pool or NULL if the metadata allocation
+ * failed.
+ */
+struct zbud_pool *zbud_create_pool(gfp_t gfp, struct zbud_ops *ops)
+{
+	struct zbud_pool *pool;
+	int i;
+
+	pool = kmalloc(sizeof(struct zbud_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;
+}
+
+/**
+ * zbud_destroy_pool() - destroys an existing zbud pool
+ * @pool:	the zbud pool to be destroyed
+ *
+ * The pool should be emptied before this function is called.
+ */
+void zbud_destroy_pool(struct zbud_pool *pool)
+{
+	kfree(pool);
+}
+
+/**
+ * zbud_alloc() - allocates a region of a given size
+ * @pool:	zbud 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 zbud pool pages.
+ *
+ * Return: 0 if success and handle is set, otherwise -EINVAL is the size or
+ * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
+ * a new page.
+ */
+int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp,
+			unsigned long *handle)
+{
+	int chunks, i, freechunks;
+	struct zbud_header *zhdr = NULL;
+	enum buddy bud;
+	struct page *page;
+
+	if (size <= 0 || gfp & __GFP_HIGHMEM)
+		return -EINVAL;
+	if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED)
+		return -ENOSPC;
+	chunks = size_to_chunks(size);
+	spin_lock(&pool->lock);
+
+	/* First, try to find an unbuddied zbud page. */
+	zhdr = NULL;
+	for_each_unbuddied_list(i, chunks) {
+		if (!list_empty(&pool->unbuddied[i])) {
+			zhdr = list_first_entry(&pool->unbuddied[i],
+					struct zbud_header, buddy);
+			list_del(&zhdr->buddy);
+			if (zhdr->first_chunks == 0)
+				bud = FIRST;
+			else
+				bud = LAST;
+			goto found;
+		}
+	}
+
+	/* Couldn't find unbuddied zbud page, create new one */
+	spin_unlock(&pool->lock);
+	page = alloc_page(gfp);
+	if (!page)
+		return -ENOMEM;
+	spin_lock(&pool->lock);
+	pool->pages_nr++;
+	zhdr = init_zbud_page(page);
+	bud = FIRST;
+
+found:
+	if (bud == FIRST)
+		zhdr->first_chunks = chunks;
+	else
+		zhdr->last_chunks = chunks;
+
+	if (zhdr->first_chunks == 0 || zhdr->last_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);
+	}
+
+	/* Add/move zbud page to beginning of LRU */
+	if (!list_empty(&zhdr->lru))
+		list_del(&zhdr->lru);
+	list_add(&zhdr->lru, &pool->lru);
+
+	*handle = encode_handle(zhdr, bud);
+	spin_unlock(&pool->lock);
+
+	return 0;
+}
+
+/**
+ * zbud_free() - frees the allocation associated with the given handle
+ * @pool:	pool in which the allocation resided
+ * @handle:	handle associated with the allocation returned by zbud_alloc()
+ *
+ * In the case that the zbud 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 zbud_reclaim_page() below).
+ */
+void zbud_free(struct zbud_pool *pool, unsigned long handle)
+{
+	struct zbud_header *zhdr;
+	int freechunks;
+
+	spin_lock(&pool->lock);
+	zhdr = handle_to_zbud_header(handle);
+
+	/* If first buddy, handle will be page aligned */
+	if ((handle - ZHDR_SIZE_ALIGNED) & ~PAGE_MASK)
+		zhdr->last_chunks = 0;
+	else
+		zhdr->first_chunks = 0;
+
+	if (zhdr->under_reclaim) {
+		/* zbud page is under reclaim, reclaim will free */
+		spin_unlock(&pool->lock);
+		return;
+	}
+
+	/* Remove from existing buddy list */
+	list_del(&zhdr->buddy);
+
+	if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
+		/* zbud page is empty, free */
+		list_del(&zhdr->lru);
+		free_zbud_page(zhdr);
+		pool->pages_nr--;
+	} else {
+		/* Add to unbuddied list */
+		freechunks = num_free_chunks(zhdr);
+		list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
+	}
+
+	spin_unlock(&pool->lock);
+}
+
+#define list_tail_entry(ptr, type, member) \
+	list_entry((ptr)->prev, type, member)
+
+/**
+ * zbud_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
+ *
+ * zbud reclaim is different from normal system reclaim in that the reclaim is
+ * done from the bottom, up.  This is because only the bottom layer, zbud, has
+ * information on how the allocations are organized within each zbud page. This
+ * has the potential to create interesting locking situations between zbud and
+ * the user, however.
+ *
+ * To avoid these, this is how zbud_reclaim_page() should be called:
+
+ * The user detects a page should be reclaimed and calls zbud_reclaim_page().
+ * zbud_reclaim_page() will remove a zbud 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. zbud_reclaim_page() will add the zbud page back to the
+ * appropriate list and try the next zbud 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 zbud_free() on the handle. zbud_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 zbud page are successfully evicted, then the
+ * zbud 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.
+ */
+int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries)
+{
+	int i, ret, freechunks;
+	struct zbud_header *zhdr;
+	unsigned long first_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++) {
+		zhdr = list_tail_entry(&pool->lru, struct zbud_header, lru);
+		list_del(&zhdr->lru);
+		list_del(&zhdr->buddy);
+		/* Protect zbud page against free */
+		zhdr->under_reclaim = true;
+		/*
+		 * 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;
+		if (zhdr->first_chunks)
+			first_handle = encode_handle(zhdr, FIRST);
+		if (zhdr->last_chunks)
+			last_handle = encode_handle(zhdr, LAST);
+		spin_unlock(&pool->lock);
+
+		/* Issue the eviction callback(s) */
+		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);
+		zhdr->under_reclaim = false;
+		if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
+			/*
+			 * Both buddies are now free, free the zbud page and
+			 * return success.
+			 */
+			free_zbud_page(zhdr);
+			pool->pages_nr--;
+			spin_unlock(&pool->lock);
+			return 0;
+		} else if (zhdr->first_chunks == 0 ||
+				zhdr->last_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);
+		}
+
+		/* add to beginning of LRU */
+		list_add(&zhdr->lru, &pool->lru);
+	}
+	spin_unlock(&pool->lock);
+	return -EAGAIN;
+}
+
+/**
+ * zbud_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
+ *
+ * While trivial for zbud, the mapping functions for others allocators
+ * implementing this allocation API could have more complex information encoded
+ * in the handle and could create temporary mappings to make the data
+ * accessible to the user.
+ *
+ * Returns: a pointer to the mapped allocation
+ */
+void *zbud_map(struct zbud_pool *pool, unsigned long handle)
+{
+	return (void *)(handle);
+}
+
+/**
+ * zbud_unmap() - maps the allocation associated with the given handle
+ * @pool:	pool in which the allocation resides
+ * @handle:	handle associated with the allocation to be unmapped
+ */
+void zbud_unmap(struct zbud_pool *pool, unsigned long handle)
+{
+}
+
+/**
+ * zbud_get_pool_size() - gets the zbud 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.
+ */
+u64 zbud_get_pool_size(struct zbud_pool *pool)
+{
+	return pool->pages_nr;
+}
+
+static int __init init_zbud(void)
+{
+	/* Make sure the zbud header will fit in one chunk */
+	BUILD_BUG_ON(sizeof(struct zbud_header) > ZHDR_SIZE_ALIGNED);
+	pr_info("loaded\n");
+	return 0;
+}
+
+static void __exit exit_zbud(void)
+{
+	pr_info("unloaded\n");
+}
+
+module_init(init_zbud);
+module_exit(exit_zbud);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
+MODULE_DESCRIPTION("Buddy Allocator for Compressed Pages");
	1	+#ifndef _ZBUD_H_
	2	+#define _ZBUD_H_
	3	+
	4	+#include <linux/types.h>
	5	+
	6	+struct zbud_pool;
	7	+
	8	+struct zbud_ops {
	9	+ int (evict)(struct zbud_pool pool, unsigned long handle);
	10	+};
	11	+
	12	+struct zbud_pool zbud_create_pool(gfp_t gfp, struct zbud_ops ops);
	13	+void zbud_destroy_pool(struct zbud_pool *pool);
	14	+int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp,
	15	+ unsigned long *handle);
	16	+void zbud_free(struct zbud_pool *pool, unsigned long handle);
	17	+int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries);
	18	+void zbud_map(struct zbud_pool pool, unsigned long handle);
	19	+void zbud_unmap(struct zbud_pool *pool, unsigned long handle);
	20	+u64 zbud_get_pool_size(struct zbud_pool *pool);
	21	+
	22	+#endif /* _ZBUD_H_ */
...	...	@@ -478,6 +478,16 @@
478	478
479	479	If unsure, say Y to enable frontswap.
480	480
	481	+config ZBUD
	482	+ tristate
	483	+ default n
	484	+ help
	485	+ A special purpose allocator for storing compressed pages.
	486	+ It is designed to store up to two compressed pages per physical
	487	+ page. While this design limits storage density, it has simple and
	488	+ deterministic reclaim properties that make it preferable to a higher
	489	+ density approach when reclaim will be used.
	490	+
481	491	config MEM_SOFT_DIRTY
482	492	bool "Track memory changes"
483	493	depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY
...	...	@@ -58,4 +58,5 @@
58	58	obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
59	59	obj-$(CONFIG_CLEANCACHE) += cleancache.o
60	60	obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
	61	+obj-$(CONFIG_ZBUD) += zbud.o
	1	+/*
	2	+ * zbud.c
	3	+ *
	4	+ * Copyright (C) 2013, Seth Jennings, IBM
	5	+ *
	6	+ * Concepts based on zcache internal zbud allocator by Dan Magenheimer.
	7	+ *
	8	+ * zbud is an special purpose allocator for storing compressed pages. Contrary
	9	+ * to what its name may suggest, zbud is not a buddy allocator, but rather an
	10	+ * allocator that "buddies" two compressed pages together in a single memory
	11	+ * page.
	12	+ *
	13	+ * While this design limits storage density, it has simple and deterministic
	14	+ * reclaim properties that make it preferable to a higher density approach when
	15	+ * reclaim will be used.
	16	+ *
	17	+ * zbud works by storing compressed pages, or "zpages", together in pairs in a
	18	+ * single memory page called a "zbud page". The first buddy is "left
	19	+ * justifed" at the beginning of the zbud page, and the last buddy is "right
	20	+ * justified" at the end of the zbud page. The benefit is that if either
	21	+ * buddy is freed, the freed buddy space, coalesced with whatever slack space
	22	+ * that existed between the buddies, results in the largest possible free region
	23	+ * within the zbud page.
	24	+ *
	25	+ * zbud also provides an attractive lower bound on density. The ratio of zpages
	26	+ * to zbud pages can not be less than 1. This ensures that zbud can never "do
	27	+ * harm" by using more pages to store zpages than the uncompressed zpages would
	28	+ * have used on their own.
	29	+ *
	30	+ * zbud pages are divided into "chunks". The size of the chunks is fixed at
	31	+ * compile time and determined by NCHUNKS_ORDER below. Dividing zbud pages
	32	+ * into chunks allows organizing unbuddied zbud pages into a manageable number
	33	+ * of unbuddied lists according to the number of free chunks available in the
	34	+ * zbud page.
	35	+ *
	36	+ * The zbud API differs from that of conventional allocators in that the
	37	+ * allocation function, zbud_alloc(), returns an opaque handle to the user,
	38	+ * not a dereferenceable pointer. The user must map the handle using
	39	+ * zbud_map() in order to get a usable pointer by which to access the
	40	+ * allocation data and unmap the handle with zbud_unmap() when operations
	41	+ * on the allocation data are complete.
	42	+ */
	43	+
	44	+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
	45	+
	46	+#include <linux/atomic.h>
	47	+#include <linux/list.h>
	48	+#include <linux/mm.h>
	49	+#include <linux/module.h>
	50	+#include <linux/preempt.h>
	51	+#include <linux/slab.h>
	52	+#include <linux/spinlock.h>
	53	+#include <linux/zbud.h>
	54	+
	55	+/*****************
	56	+ * Structures
	57	+*****************/
	58	+/*
	59	+ * NCHUNKS_ORDER determines the internal allocation granularity, effectively
	60	+ * adjusting internal fragmentation. It also determines the number of
	61	+ * freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the
	62	+ * allocation granularity will be in chunks of size PAGE_SIZE/64, and there
	63	+ * will be 64 freelists per pool.
	64	+ */
	65	+#define NCHUNKS_ORDER 6
	66	+
	67	+#define CHUNK_SHIFT (PAGE_SHIFT - NCHUNKS_ORDER)
	68	+#define CHUNK_SIZE (1 << CHUNK_SHIFT)
	69	+#define NCHUNKS (PAGE_SIZE >> CHUNK_SHIFT)
	70	+#define ZHDR_SIZE_ALIGNED CHUNK_SIZE
	71	+
	72	+/**
	73	+ * struct zbud_pool - stores metadata for each zbud pool
	74	+ * @lock: protects all pool fields and first\|last_chunk fields of any
	75	+ * zbud page in the pool
	76	+ * @unbuddied: array of lists tracking zbud pages that only contain one buddy;
	77	+ * the lists each zbud page is added to depends on the size of
	78	+ * its free region.
	79	+ * @buddied: list tracking the zbud pages that contain two buddies;
	80	+ * these zbud pages are full
	81	+ * @lru: list tracking the zbud pages in LRU order by most recently
	82	+ * added buddy.
	83	+ * @pages_nr: number of zbud pages in the pool.
	84	+ * @ops: pointer to a structure of user defined operations specified at
	85	+ * pool creation time.
	86	+ *
	87	+ * This structure is allocated at pool creation time and maintains metadata
	88	+ * pertaining to a particular zbud pool.
	89	+ */
	90	+struct zbud_pool {
	91	+ spinlock_t lock;
	92	+ struct list_head unbuddied[NCHUNKS];
	93	+ struct list_head buddied;
	94	+ struct list_head lru;
	95	+ u64 pages_nr;
	96	+ struct zbud_ops *ops;
	97	+};
	98	+
	99	+/*
	100	+ * struct zbud_header - zbud page metadata occupying the first chunk of each
	101	+ * zbud page.
	102	+ * @buddy: links the zbud page into the unbuddied/buddied lists in the pool
	103	+ * @lru: links the zbud page into the lru list in the pool
	104	+ * @first_chunks: the size of the first buddy in chunks, 0 if free
	105	+ * @last_chunks: the size of the last buddy in chunks, 0 if free
	106	+ */
	107	+struct zbud_header {
	108	+ struct list_head buddy;
	109	+ struct list_head lru;
	110	+ unsigned int first_chunks;
	111	+ unsigned int last_chunks;
	112	+ bool under_reclaim;
	113	+};
	114	+
	115	+/*****************
	116	+ * Helpers
	117	+*****************/
	118	+/* Just to make the code easier to read */
	119	+enum buddy {
	120	+ FIRST,
	121	+ LAST
	122	+};
	123	+
	124	+/* Converts an allocation size in bytes to size in zbud chunks */
	125	+static int size_to_chunks(int size)
	126	+{
	127	+ return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
	128	+}
	129	+
	130	+#define for_each_unbuddied_list(_iter, _begin) \
	131	+ for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
	132	+
	133	+/* Initializes the zbud header of a newly allocated zbud page */
	134	+static struct zbud_header init_zbud_page(struct page page)
	135	+{
	136	+ struct zbud_header *zhdr = page_address(page);
	137	+ zhdr->first_chunks = 0;
	138	+ zhdr->last_chunks = 0;
	139	+ INIT_LIST_HEAD(&zhdr->buddy);
	140	+ INIT_LIST_HEAD(&zhdr->lru);
	141	+ zhdr->under_reclaim = 0;
	142	+ return zhdr;
	143	+}
	144	+
	145	+/* Resets the struct page fields and frees the page */
	146	+static void free_zbud_page(struct zbud_header *zhdr)
	147	+{
	148	+ __free_page(virt_to_page(zhdr));
	149	+}
	150	+
	151	+/*
	152	+ * Encodes the handle of a particular buddy within a zbud page
	153	+ * Pool lock should be held as this function accesses first\|last_chunks
	154	+ */
	155	+static unsigned long encode_handle(struct zbud_header *zhdr, enum buddy bud)
	156	+{
	157	+ unsigned long handle;
	158	+
	159	+ /*
	160	+ * For now, the encoded handle is actually just the pointer to the data
	161	+ * but this might not always be the case. A little information hiding.
	162	+ * Add CHUNK_SIZE to the handle if it is the first allocation to jump
	163	+ * over the zbud header in the first chunk.
	164	+ */
	165	+ handle = (unsigned long)zhdr;
	166	+ if (bud == FIRST)
	167	+ /* skip over zbud header */
	168	+ handle += ZHDR_SIZE_ALIGNED;
	169	+ else /* bud == LAST */
	170	+ handle += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
	171	+ return handle;
	172	+}
	173	+
	174	+/* Returns the zbud page where a given handle is stored */
	175	+static struct zbud_header *handle_to_zbud_header(unsigned long handle)
	176	+{
	177	+ return (struct zbud_header *)(handle & PAGE_MASK);
	178	+}
	179	+
	180	+/* Returns the number of free chunks in a zbud page */
	181	+static int num_free_chunks(struct zbud_header *zhdr)
	182	+{
	183	+ /*
	184	+ * Rather than branch for different situations, just use the fact that
	185	+ * free buddies have a length of zero to simplify everything. -1 at the
	186	+ * end for the zbud header.
	187	+ */
	188	+ return NCHUNKS - zhdr->first_chunks - zhdr->last_chunks - 1;
	189	+}
	190	+
	191	+/*****************
	192	+ * API Functions
	193	+*****************/
	194	+/**
	195	+ * zbud_create_pool() - create a new zbud pool
	196	+ * @gfp: gfp flags when allocating the zbud pool structure
	197	+ * @ops: user-defined operations for the zbud pool
	198	+ *
	199	+ * Return: pointer to the new zbud pool or NULL if the metadata allocation
	200	+ * failed.
	201	+ */
	202	+struct zbud_pool zbud_create_pool(gfp_t gfp, struct zbud_ops ops)
	203	+{
	204	+ struct zbud_pool *pool;
	205	+ int i;
	206	+
	207	+ pool = kmalloc(sizeof(struct zbud_pool), gfp);
	208	+ if (!pool)
	209	+ return NULL;
	210	+ spin_lock_init(&pool->lock);
	211	+ for_each_unbuddied_list(i, 0)
	212	+ INIT_LIST_HEAD(&pool->unbuddied[i]);
	213	+ INIT_LIST_HEAD(&pool->buddied);
	214	+ INIT_LIST_HEAD(&pool->lru);
	215	+ pool->pages_nr = 0;
	216	+ pool->ops = ops;
	217	+ return pool;
	218	+}
	219	+
	220	+/**
	221	+ * zbud_destroy_pool() - destroys an existing zbud pool
	222	+ * @pool: the zbud pool to be destroyed
	223	+ *
	224	+ * The pool should be emptied before this function is called.
	225	+ */
	226	+void zbud_destroy_pool(struct zbud_pool *pool)
	227	+{
	228	+ kfree(pool);
	229	+}
	230	+
	231	+/**
	232	+ * zbud_alloc() - allocates a region of a given size
	233	+ * @pool: zbud pool from which to allocate
	234	+ * @size: size in bytes of the desired allocation
	235	+ * @gfp: gfp flags used if the pool needs to grow
	236	+ * @handle: handle of the new allocation
	237	+ *
	238	+ * This function will attempt to find a free region in the pool large enough to
	239	+ * satisfy the allocation request. A search of the unbuddied lists is
	240	+ * performed first. If no suitable free region is found, then a new page is
	241	+ * allocated and added to the pool to satisfy the request.
	242	+ *
	243	+ * gfp should not set __GFP_HIGHMEM as highmem pages cannot be used
	244	+ * as zbud pool pages.
	245	+ *
	246	+ * Return: 0 if success and handle is set, otherwise -EINVAL is the size or
	247	+ * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
	248	+ * a new page.
	249	+ */
	250	+int zbud_alloc(struct zbud_pool *pool, int size, gfp_t gfp,
	251	+ unsigned long *handle)
	252	+{
	253	+ int chunks, i, freechunks;
	254	+ struct zbud_header *zhdr = NULL;
	255	+ enum buddy bud;
	256	+ struct page *page;
	257	+
	258	+ if (size <= 0 \|\| gfp & __GFP_HIGHMEM)
	259	+ return -EINVAL;
	260	+ if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED)
	261	+ return -ENOSPC;
	262	+ chunks = size_to_chunks(size);
	263	+ spin_lock(&pool->lock);
	264	+
	265	+ /* First, try to find an unbuddied zbud page. */
	266	+ zhdr = NULL;
	267	+ for_each_unbuddied_list(i, chunks) {
	268	+ if (!list_empty(&pool->unbuddied[i])) {
	269	+ zhdr = list_first_entry(&pool->unbuddied[i],
	270	+ struct zbud_header, buddy);
	271	+ list_del(&zhdr->buddy);
	272	+ if (zhdr->first_chunks == 0)
	273	+ bud = FIRST;
	274	+ else
	275	+ bud = LAST;
	276	+ goto found;
	277	+ }
	278	+ }
	279	+
	280	+ /* Couldn't find unbuddied zbud page, create new one */
	281	+ spin_unlock(&pool->lock);
	282	+ page = alloc_page(gfp);
	283	+ if (!page)
	284	+ return -ENOMEM;
	285	+ spin_lock(&pool->lock);
	286	+ pool->pages_nr++;
	287	+ zhdr = init_zbud_page(page);
	288	+ bud = FIRST;
	289	+
	290	+found:
	291	+ if (bud == FIRST)
	292	+ zhdr->first_chunks = chunks;
	293	+ else
	294	+ zhdr->last_chunks = chunks;
	295	+
	296	+ if (zhdr->first_chunks == 0 \|\| zhdr->last_chunks == 0) {
	297	+ /* Add to unbuddied list */
	298	+ freechunks = num_free_chunks(zhdr);
	299	+ list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
	300	+ } else {
	301	+ /* Add to buddied list */
	302	+ list_add(&zhdr->buddy, &pool->buddied);
	303	+ }
	304	+
	305	+ /* Add/move zbud page to beginning of LRU */
	306	+ if (!list_empty(&zhdr->lru))
	307	+ list_del(&zhdr->lru);
	308	+ list_add(&zhdr->lru, &pool->lru);
	309	+
	310	+ *handle = encode_handle(zhdr, bud);
	311	+ spin_unlock(&pool->lock);
	312	+
	313	+ return 0;
	314	+}
	315	+
	316	+/**
	317	+ * zbud_free() - frees the allocation associated with the given handle
	318	+ * @pool: pool in which the allocation resided
	319	+ * @handle: handle associated with the allocation returned by zbud_alloc()
	320	+ *
	321	+ * In the case that the zbud page in which the allocation resides is under
	322	+ * reclaim, as indicated by the PG_reclaim flag being set, this function
	323	+ * only sets the first\|last_chunks to 0. The page is actually freed
	324	+ * once both buddies are evicted (see zbud_reclaim_page() below).
	325	+ */
	326	+void zbud_free(struct zbud_pool *pool, unsigned long handle)
	327	+{
	328	+ struct zbud_header *zhdr;
	329	+ int freechunks;
	330	+
	331	+ spin_lock(&pool->lock);
	332	+ zhdr = handle_to_zbud_header(handle);
	333	+
	334	+ /* If first buddy, handle will be page aligned */
	335	+ if ((handle - ZHDR_SIZE_ALIGNED) & ~PAGE_MASK)
	336	+ zhdr->last_chunks = 0;
	337	+ else
	338	+ zhdr->first_chunks = 0;
	339	+
	340	+ if (zhdr->under_reclaim) {
	341	+ /* zbud page is under reclaim, reclaim will free */
	342	+ spin_unlock(&pool->lock);
	343	+ return;
	344	+ }
	345	+
	346	+ /* Remove from existing buddy list */
	347	+ list_del(&zhdr->buddy);
	348	+
	349	+ if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
	350	+ /* zbud page is empty, free */
	351	+ list_del(&zhdr->lru);
	352	+ free_zbud_page(zhdr);
	353	+ pool->pages_nr--;
	354	+ } else {
	355	+ /* Add to unbuddied list */
	356	+ freechunks = num_free_chunks(zhdr);
	357	+ list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
	358	+ }
	359	+
	360	+ spin_unlock(&pool->lock);
	361	+}
	362	+
	363	+#define list_tail_entry(ptr, type, member) \
	364	+ list_entry((ptr)->prev, type, member)
	365	+
	366	+/**
	367	+ * zbud_reclaim_page() - evicts allocations from a pool page and frees it
	368	+ * @pool: pool from which a page will attempt to be evicted
	369	+ * @retires: number of pages on the LRU list for which eviction will
	370	+ * be attempted before failing
	371	+ *
	372	+ * zbud reclaim is different from normal system reclaim in that the reclaim is
	373	+ * done from the bottom, up. This is because only the bottom layer, zbud, has
	374	+ * information on how the allocations are organized within each zbud page. This
	375	+ * has the potential to create interesting locking situations between zbud and
	376	+ * the user, however.
	377	+ *
	378	+ * To avoid these, this is how zbud_reclaim_page() should be called:
	379	+
	380	+ * The user detects a page should be reclaimed and calls zbud_reclaim_page().
	381	+ * zbud_reclaim_page() will remove a zbud page from the pool LRU list and call
	382	+ * the user-defined eviction handler with the pool and handle as arguments.
	383	+ *
	384	+ * If the handle can not be evicted, the eviction handler should return
	385	+ * non-zero. zbud_reclaim_page() will add the zbud page back to the
	386	+ * appropriate list and try the next zbud page on the LRU up to
	387	+ * a user defined number of retries.
	388	+ *
	389	+ * If the handle is successfully evicted, the eviction handler should
	390	+ * return 0 _and_ should have called zbud_free() on the handle. zbud_free()
	391	+ * contains logic to delay freeing the page if the page is under reclaim,
	392	+ * as indicated by the setting of the PG_reclaim flag on the underlying page.
	393	+ *
	394	+ * If all buddies in the zbud page are successfully evicted, then the
	395	+ * zbud page can be freed.
	396	+ *
	397	+ * Returns: 0 if page is successfully freed, otherwise -EINVAL if there are
	398	+ * no pages to evict or an eviction handler is not registered, -EAGAIN if
	399	+ * the retry limit was hit.
	400	+ */
	401	+int zbud_reclaim_page(struct zbud_pool *pool, unsigned int retries)
	402	+{
	403	+ int i, ret, freechunks;
	404	+ struct zbud_header *zhdr;
	405	+ unsigned long first_handle = 0, last_handle = 0;
	406	+
	407	+ spin_lock(&pool->lock);
	408	+ if (!pool->ops \|\| !pool->ops->evict \|\| list_empty(&pool->lru) \|\|
	409	+ retries == 0) {
	410	+ spin_unlock(&pool->lock);
	411	+ return -EINVAL;
	412	+ }
	413	+ for (i = 0; i < retries; i++) {
	414	+ zhdr = list_tail_entry(&pool->lru, struct zbud_header, lru);
	415	+ list_del(&zhdr->lru);
	416	+ list_del(&zhdr->buddy);
	417	+ /* Protect zbud page against free */
	418	+ zhdr->under_reclaim = true;
	419	+ /*
	420	+ * We need encode the handles before unlocking, since we can
	421	+ * race with free that will set (first\|last)_chunks to 0
	422	+ */
	423	+ first_handle = 0;
	424	+ last_handle = 0;
	425	+ if (zhdr->first_chunks)
	426	+ first_handle = encode_handle(zhdr, FIRST);
	427	+ if (zhdr->last_chunks)
	428	+ last_handle = encode_handle(zhdr, LAST);
	429	+ spin_unlock(&pool->lock);
	430	+
	431	+ /* Issue the eviction callback(s) */
	432	+ if (first_handle) {
	433	+ ret = pool->ops->evict(pool, first_handle);
	434	+ if (ret)
	435	+ goto next;
	436	+ }
	437	+ if (last_handle) {
	438	+ ret = pool->ops->evict(pool, last_handle);
	439	+ if (ret)
	440	+ goto next;
	441	+ }
	442	+next:
	443	+ spin_lock(&pool->lock);
	444	+ zhdr->under_reclaim = false;
	445	+ if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
	446	+ /*
	447	+ * Both buddies are now free, free the zbud page and
	448	+ * return success.
	449	+ */
	450	+ free_zbud_page(zhdr);
	451	+ pool->pages_nr--;
	452	+ spin_unlock(&pool->lock);
	453	+ return 0;
	454	+ } else if (zhdr->first_chunks == 0 \|\|
	455	+ zhdr->last_chunks == 0) {
	456	+ /* add to unbuddied list */
	457	+ freechunks = num_free_chunks(zhdr);
	458	+ list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
	459	+ } else {
	460	+ /* add to buddied list */
	461	+ list_add(&zhdr->buddy, &pool->buddied);
	462	+ }
	463	+
	464	+ /* add to beginning of LRU */
	465	+ list_add(&zhdr->lru, &pool->lru);
	466	+ }
	467	+ spin_unlock(&pool->lock);
	468	+ return -EAGAIN;
	469	+}
	470	+
	471	+/**
	472	+ * zbud_map() - maps the allocation associated with the given handle
	473	+ * @pool: pool in which the allocation resides
	474	+ * @handle: handle associated with the allocation to be mapped
	475	+ *
	476	+ * While trivial for zbud, the mapping functions for others allocators
	477	+ * implementing this allocation API could have more complex information encoded
	478	+ * in the handle and could create temporary mappings to make the data
	479	+ * accessible to the user.
	480	+ *
	481	+ * Returns: a pointer to the mapped allocation
	482	+ */
	483	+void zbud_map(struct zbud_pool pool, unsigned long handle)
	484	+{
	485	+ return (void *)(handle);
	486	+}
	487	+
	488	+/**
	489	+ * zbud_unmap() - maps the allocation associated with the given handle
	490	+ * @pool: pool in which the allocation resides
	491	+ * @handle: handle associated with the allocation to be unmapped
	492	+ */
	493	+void zbud_unmap(struct zbud_pool *pool, unsigned long handle)
	494	+{
	495	+}
	496	+
	497	+/**
	498	+ * zbud_get_pool_size() - gets the zbud pool size in pages
	499	+ * @pool: pool whose size is being queried
	500	+ *
	501	+ * Returns: size in pages of the given pool. The pool lock need not be
	502	+ * taken to access pages_nr.
	503	+ */
	504	+u64 zbud_get_pool_size(struct zbud_pool *pool)
	505	+{
	506	+ return pool->pages_nr;
	507	+}
	508	+
	509	+static int __init init_zbud(void)
	510	+{
	511	+ /* Make sure the zbud header will fit in one chunk */
	512	+ BUILD_BUG_ON(sizeof(struct zbud_header) > ZHDR_SIZE_ALIGNED);
	513	+ pr_info("loaded\n");
	514	+ return 0;
	515	+}
	516	+
	517	+static void __exit exit_zbud(void)
	518	+{
	519	+ pr_info("unloaded\n");
	520	+}
	521	+
	522	+module_init(init_zbud);
	523	+module_exit(exit_zbud);
	524	+
	525	+MODULE_LICENSE("GPL");
	526	+MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
	527	+MODULE_DESCRIPTION("Buddy Allocator for Compressed Pages");