Message-Id: <1314801641-15059-2-git-send-email-sjenning@linux.vnet.ibm.com>
Date:	Wed, 31 Aug 2011 09:40:39 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	gregkh@...e.de
Cc:	devel@...verdev.osuosl.org, dan.magenheimer@...cle.com,
	ngupta@...are.org, cascardo@...oscopio.com, rdunlap@...otime.net,
	linux-kernel@...r.kernel.org,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Subject: [PATCH 1/3] staging: zcache: xcfmalloc memory allocator for zcache

xcfmalloc is a memory allocator based on a scatter-gather model that
allows for cross-page storage and relocatable data blocks.  This is
achieved through a simple, though non-standard, memory allocation API.

xcfmalloc is a replacement for the xvmalloc allocator used by zcache
for persistent compressed page storage.

xcfmalloc uses a scatter-gather block model in order to reduce external
fragmentation (at the expense of an extra memcpy).  Low fragmentation
is especially important for a zcache allocator since memory will already
be under pressure.

It also uses relocatable data blocks in order to allow compaction to take
place.  Compacting seeks to move blocks to other, less sparsely used,
pages such that the maximum number of pages can be returned to the kernel
buddy allocator. Compaction is not yet implemented in this patch.

Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
---
 drivers/staging/zcache/Makefile    |    2 +-
 drivers/staging/zcache/xcfmalloc.c |  653 ++++++++++++++++++++++++++++++++++++
 drivers/staging/zcache/xcfmalloc.h |   29 ++
 3 files changed, 683 insertions(+), 1 deletions(-)
 create mode 100644 drivers/staging/zcache/xcfmalloc.c
 create mode 100644 drivers/staging/zcache/xcfmalloc.h

diff --git a/drivers/staging/zcache/Makefile b/drivers/staging/zcache/Makefile
index 60daa27..c7aa772 100644
--- a/drivers/staging/zcache/Makefile
+++ b/drivers/staging/zcache/Makefile
@@ -1,3 +1,3 @@
-zcache-y	:=	zcache-main.o tmem.o
+zcache-y	:=	zcache-main.o tmem.o xcfmalloc.o
 
 obj-$(CONFIG_ZCACHE)	+=	zcache.o
diff --git a/drivers/staging/zcache/xcfmalloc.c b/drivers/staging/zcache/xcfmalloc.c
new file mode 100644
index 0000000..0c6bf49
--- /dev/null
+++ b/drivers/staging/zcache/xcfmalloc.c
@@ -0,0 +1,653 @@
+/* xcfmalloc.c */
+
+/*
+ * xcfmalloc is a memory allocator based on a scatter-gather model that
+ * allows for cross-page storage and relocatable data blocks.  This is
+ * achieved through a simple, though non-standard, memory allocation API.
+ *
+ * xcfmalloc is a replacement for the xvmalloc allocator used by zcache
+ * for persistent compressed page storage.
+ *
+ * xcfmalloc uses a scatter-gather block model in order to reduce external
+ * fragmentation (at the expense of an extra memcpy).  Low fragmentation
+ * is especially important for a zcache allocator since memory will already
+ * be under pressure.
+ *
+ * It also uses relocatable data blocks in order to allow compaction to take
+ * place.  Compacting seeks to move blocks to other, less sparsely used,
+ * pages such that the maximum number of pages can be returned to the kernel
+ * buddy allocator.  NOTE: Compaction is not yet implemented.
+*/
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/bitops.h>
+#include <linux/errno.h>
+#include <linux/highmem.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+
+#include "xcfmalloc.h"
+
+/* turn debugging on */
+#define XCFM_DEBUG
+
+/* tunables */
+#define XCF_BLOCK_SHIFT 6
+#define XCF_MAX_RESERVE_PAGES 32
+#define XCF_MAX_BLOCKS_PER_ALLOC 2
+
+#define XCF_BLOCK_ALIGN (1 << XCF_BLOCK_SHIFT)
+#define XCF_NUM_FREELISTS (PAGE_SIZE >> XCF_BLOCK_SHIFT)
+#define XCF_RESERVED_INDEX (XCF_NUM_FREELISTS - 1)
+
+static inline int xcf_align_to_block(int size)
+{
+	return ALIGN(size, XCF_BLOCK_ALIGN);
+}
+
+static inline int xcf_size_to_flindex(int size)
+{
+
+	return (xcf_align_to_block(size) >> XCF_BLOCK_SHIFT) - 1;
+}
+
+/* pool structure */
+struct xcf_pool {
+	struct xcf_blkdesc *freelists[XCF_NUM_FREELISTS];
+	spinlock_t lock;
+	gfp_t flags; /* flags used for page allocations */
+	int reserve_count; /* number of reserved (completely unused) pages */
+	int page_count; /* number of pages used and reserved */
+	int desc_count; /* number of block descriptors */
+};
+
+/* block descriptor structure and helper functions */
+struct xcf_blkdesc {
+	struct page *page;
+	struct xcf_blkdesc *next;
+	struct xcf_blkdesc *prev;
+	int offxcf_set_flags;
+#define XCF_FLAG_MASK (XCF_BLOCK_ALIGN - 1)
+#define XCF_OFFSET_MASK (~XCF_FLAG_MASK)
+#define XCF_BLOCK_FREE (1<<0)
+#define XCF_BLOCK_USED (1<<1)
+	/* size means different things depending on whether the block is
+	 * in use or not. If the block is free, the size is the aligned size
+	 * of the block and the block can contain an allocation of up to
+	 * (size - sizeof(struct xcf_blkhdr)). If the block is in use,
+	 * size is the actual number of bytes used by the allocation plus
+	 * sizeof(struct xcf_blkhdr) */
+	int size;
+};
+
+static inline void xcf_set_offset(struct xcf_blkdesc *desc, int offset)
+{
+	BUG_ON(offset != (offset & XCF_OFFSET_MASK));
+	desc->offxcf_set_flags = offset |
+		(desc->offxcf_set_flags & XCF_FLAG_MASK);
+}
+
+static inline int xcf_get_offset(struct xcf_blkdesc *desc)
+{
+	return desc->offxcf_set_flags & XCF_OFFSET_MASK;
+}
+
+static inline void xcf_set_flags(struct xcf_blkdesc *desc, int flags)
+{
+	BUG_ON(flags != (flags & XCF_FLAG_MASK));
+	desc->offxcf_set_flags = flags |
+		(desc->offxcf_set_flags & XCF_OFFSET_MASK);
+}
+
+static inline bool xcf_is_free(struct xcf_blkdesc *desc)
+{
+	return desc->offxcf_set_flags & XCF_BLOCK_FREE;
+}
+
+static inline bool xcf_is_used(struct xcf_blkdesc *desc)
+{
+	return desc->offxcf_set_flags & XCF_BLOCK_USED;
+}
+
+/* block header structure and helper functions */
+#ifdef XCFM_DEBUG
+#define DECL_SENTINEL int sentinel
+#define SENTINEL 0xdeadbeef
+#define SET_SENTINEL(_obj) ((_obj)->sentinel = SENTINEL)
+#define ASSERT_SENTINEL(_obj) BUG_ON((_obj)->sentinel != SENTINEL)
+#define CLEAR_SENTINEL(_obj) ((_obj)->sentinel = 0)
+#else
+#define DECL_SENTINEL
+#define SET_SENTINEL(_obj) do { } while (0)
+#define ASSERT_SENTINEL(_obj) do { } while (0)
+#define CLEAR_SENTINEL(_obj) do { } while (0)
+#endif
+
+struct xcf_blkhdr {
+	struct xcf_blkdesc *desc;
+	int prevoffset;
+	DECL_SENTINEL;
+};
+
+#define MAX_ALLOC_SIZE (PAGE_SIZE - sizeof(struct xcf_blkhdr))
+
+static inline void *xcf_page_start(struct xcf_blkhdr *block)
+{
+	return (void *)((unsigned long)block & PAGE_MASK);
+}
+
+static inline struct xcf_blkhdr *xcf_block_offset(struct xcf_blkhdr *block,
+						int offset)
+{
+	return (struct xcf_blkhdr *)((char *)block + offset);
+}
+
+static inline bool xcf_same_page(struct xcf_blkhdr *block1,
+				struct xcf_blkhdr *block2)
+{
+	return (xcf_page_start(block1) == xcf_page_start(block2));
+}
+
+static inline void *__xcf_map_block(struct xcf_blkdesc *desc,
+					enum km_type type)
+{
+	return kmap_atomic(desc->page, type) + xcf_get_offset(desc);
+}
+
+static inline void *xcf_map_block(struct xcf_blkdesc *desc, enum km_type type)
+{
+	struct xcf_blkhdr *block;
+	block = __xcf_map_block(desc, type);
+	ASSERT_SENTINEL(block);
+	return block;
+}
+
+static inline void xcf_unmap_block(struct xcf_blkhdr *block, enum km_type type)
+{
+	kunmap_atomic(xcf_page_start(block), type);
+}
+
+/* descriptor memory cache */
+static struct kmem_cache *xcf_desc_cache;
+
+/* descriptor management */
+
+struct xcf_blkdesc *xcf_alloc_desc(struct xcf_pool *pool, gfp_t flags)
+{
+	struct xcf_blkdesc *desc;
+	desc = kmem_cache_zalloc(xcf_desc_cache, flags);
+	if (desc)
+		pool->desc_count++;
+	return desc;
+}
+
+void xcf_free_desc(struct xcf_pool *pool, struct xcf_blkdesc *desc)
+{
+	kmem_cache_free(xcf_desc_cache, desc);
+	pool->desc_count--;
+}
+
+/* block management */
+
+static void xcf_remove_block(struct xcf_pool *pool, struct xcf_blkdesc *desc)
+{
+	u32 flindex;
+
+	BUG_ON(!xcf_is_free(desc));
+	flindex = xcf_size_to_flindex(desc->size);
+	if (flindex == XCF_RESERVED_INDEX)
+		pool->reserve_count--;
+	if (pool->freelists[flindex] == desc)
+		pool->freelists[flindex] = desc->next;
+	if (desc->prev)
+		desc->prev->next = desc->next;
+	if (desc->next)
+		desc->next->prev = desc->prev;
+	desc->next = NULL;
+	desc->prev = NULL;
+}
+
+static void xcf_insert_block(struct xcf_pool *pool, struct xcf_blkdesc *desc)
+{
+	u32 flindex;
+
+	flindex = xcf_size_to_flindex(desc->size);
+	if (flindex == XCF_RESERVED_INDEX)
+		pool->reserve_count++;
+	/* the block size needs to be realigned since it was previously
+	 * set to the actual allocation size */
+	desc->size = xcf_align_to_block(desc->size);
+	desc->next = pool->freelists[flindex];
+	desc->prev = NULL;
+	xcf_set_flags(desc, XCF_BLOCK_FREE);
+	pool->freelists[flindex] = desc;
+	if (desc->next)
+		desc->next->prev = desc;
+}
+
+/*
+ * The xcf_find_remove_block function contains the block selection logic for
+ * this allocator.
+ *
+ * This selection pattern has the advantage of utilizing blocks in partially
+ * used pages before considering a completely unused page.  This results
+ * in high utilization of the pool pages and the expense of higher allocation
+ * fragmentation (i.e. more blocks per allocation).  This is acceptable
+ * though since, at this point, memory is the resource under pressure.
+*/
+static struct xcf_blkdesc *xcf_find_remove_block(struct xcf_pool *pool,
+	int size, int blocknum)
+{
+	int flindex, i;
+	struct xcf_blkdesc *desc = NULL;
+
+	flindex = xcf_size_to_flindex(size + sizeof(struct xcf_blkhdr));
+
+	/* look for best fit */
+	if (pool->freelists[flindex])
+		goto remove;
+
+	/* if this is the last block allowed in the allocation, we shouldn't
+	 * consider smaller blocks.  it's all or nothing now */
+	if (blocknum == XCF_MAX_BLOCKS_PER_ALLOC) {
+		/* look for largest smaller block */
+		for (i = flindex; i > 0; i--) {
+			if (pool->freelists[i]) {
+				flindex = i;
+				goto remove;
+			}
+		}
+	}
+
+	/* look for smallest larger block */
+	for (i = flindex + 1; i < XCF_NUM_FREELISTS; i++) {
+		if (pool->freelists[i]) {
+			flindex = i;
+			goto remove;
+		}
+	}
+
+	/* if we get here, there are no blocks that satisfy the request */
+	return NULL;
+
+remove:
+	desc = pool->freelists[flindex];
+	xcf_remove_block(pool, desc);
+	return desc;
+}
+
+struct xcf_blkdesc *xcf_merge_free_block(struct xcf_pool *pool,
+					struct xcf_blkdesc *desc)
+{
+	struct xcf_blkdesc *next, *prev;
+	struct xcf_blkhdr *block, *nextblock, *prevblock;
+
+	block = xcf_map_block(desc, KM_USER0);
+
+	prevblock = xcf_block_offset(xcf_page_start(block), block->prevoffset);
+	if (xcf_get_offset(desc) == 0) {
+		prev = NULL;
+	} else {
+		ASSERT_SENTINEL(prevblock);
+		prev = prevblock->desc;
+	}
+
+	nextblock = xcf_block_offset(block, desc->size);
+	if (!xcf_same_page(block, nextblock)) {
+		next = NULL;
+	} else {
+		ASSERT_SENTINEL(nextblock);
+		next = nextblock->desc;
+	}
+
+	/* merge adjacent free blocks in page */
+	if (prev && xcf_is_free(prev)) {
+		/* merge with previous block */
+		xcf_remove_block(pool, prev);
+		prev->size += desc->size;
+		xcf_free_desc(pool, desc);
+		CLEAR_SENTINEL(block);
+		desc = prev;
+		block = prevblock;
+	}
+
+	if (next && xcf_is_free(next)) {
+		/* merge with next block */
+		xcf_remove_block(pool, next);
+		desc->size += next->size;
+		CLEAR_SENTINEL(nextblock);
+		nextblock = xcf_block_offset(nextblock, next->size);
+		xcf_free_desc(pool, next);
+		if (!xcf_same_page(nextblock, block)) {
+			next = NULL;
+		} else {
+			ASSERT_SENTINEL(nextblock);
+			next = nextblock->desc;
+		}
+	}
+
+	if (next)
+		nextblock->prevoffset = xcf_get_offset(desc);
+
+	xcf_unmap_block(block, KM_USER0);
+
+	return desc;
+}
+
+/* pool management */
+
+/* try to get pool->reserve_count up to XCF_MAX_RESERVE_PAGES */
+static void xcf_increase_pool(struct xcf_pool *pool, gfp_t flags)
+{
+	struct xcf_blkdesc *desc;
+	int deficit_pages;
+	struct xcf_blkhdr *block;
+	struct page *page;
+
+	/* if we are at or above our desired number of
+	 * reserved pages, nothing to do */
+	if (pool->reserve_count >= XCF_MAX_RESERVE_PAGES)
+		return;
+
+	/* alloc some pages (if we can) */
+	deficit_pages = XCF_MAX_RESERVE_PAGES - pool->reserve_count;
+	while (deficit_pages--) {
+		desc = xcf_alloc_desc(pool, GFP_NOWAIT);
+		if (!desc)
+			break;
+		/* we use our own scatter-gather mechanism that maps high
+		 * memory pages under the covers, so we add HIGHMEM
+		 * even if the caller did not explicitly request it */
+		page = alloc_page(flags | __GFP_HIGHMEM);
+		if (!page) {
+			xcf_free_desc(pool, desc);
+			break;
+		}
+		pool->page_count++;
+		desc->page = page;
+		xcf_set_offset(desc, 0);
+		desc->size = PAGE_SIZE;
+		xcf_insert_block(pool, desc);
+		block = __xcf_map_block(desc, KM_USER0);
+		block->desc = desc;
+		block->prevoffset = 0;
+		SET_SENTINEL(block);
+		xcf_unmap_block(block, KM_USER0);
+	}
+}
+
+/* tries to get pool->reserve_count down to XCF_MAX_RESERVE_PAGES */
+static void xcf_decrease_pool(struct xcf_pool *pool)
+{
+	struct xcf_blkdesc *desc;
+	int surplus_pages;
+
+	/* if we are at are below our desired number of
+	 * reserved pages, nothing to do */
+	if (pool->reserve_count <= XCF_MAX_RESERVE_PAGES)
+		return;
+
+	/* free some pages */
+	surplus_pages = pool->reserve_count - XCF_MAX_RESERVE_PAGES;
+	while (surplus_pages--) {
+		desc = pool->freelists[XCF_RESERVED_INDEX];
+		BUG_ON(!desc);
+		xcf_remove_block(pool, desc);
+		__free_page(desc->page);
+		pool->page_count--;
+		xcf_free_desc(pool, desc);
+	}
+}
+
+/* public functions */
+
+/* return handle to new descect with specified size */
+void *xcf_malloc(struct xcf_pool *pool, int size, gfp_t flags)
+{
+	struct xcf_blkdesc *first, *prev, *next, *desc, *splitdesc;
+	int i, sizeleft, alignedleft;
+	struct xcf_blkhdr *block, *nextblock, *splitblock;
+
+	if (size > MAX_ALLOC_SIZE)
+		return NULL;
+
+	spin_lock(&pool->lock);
+
+	/* check and possibly increase (alloc) pool's page reserves */
+	xcf_increase_pool(pool, flags);
+
+	sizeleft = size;
+	first = NULL;
+	prev = NULL;
+
+	/* find block(s) to contain the allocation */
+	for (i = 1; i <= XCF_MAX_BLOCKS_PER_ALLOC; i++) {
+		desc = xcf_find_remove_block(pool, sizeleft, i);
+		if (!desc)
+			goto return_blocks;
+		if (!first)
+			first = desc;
+		desc->prev = prev;
+		if (prev)
+			prev->next = desc;
+		xcf_set_flags(desc, XCF_BLOCK_USED);
+		if (desc->size >= sizeleft + sizeof(struct xcf_blkhdr))
+			break;
+		sizeleft -= desc->size - sizeof(struct xcf_blkhdr);
+		prev = desc;
+	}
+
+	/* split is only possible on the last block */
+	alignedleft = xcf_align_to_block(sizeleft + sizeof(struct xcf_blkhdr));
+	if (desc->size > alignedleft) {
+		splitdesc = xcf_alloc_desc(pool, GFP_NOWAIT);
+		if (!splitdesc)
+			goto return_blocks;
+		splitdesc->size = desc->size - alignedleft;
+		splitdesc->page = desc->page;
+		xcf_set_offset(splitdesc, xcf_get_offset(desc) + alignedleft);
+
+		block = xcf_map_block(desc, KM_USER0);
+		ASSERT_SENTINEL(block);
+		nextblock = xcf_block_offset(block, desc->size);
+		if (xcf_same_page(nextblock, block))
+			nextblock->prevoffset = xcf_get_offset(splitdesc);
+		splitblock = xcf_block_offset(block, alignedleft);
+		splitblock->desc = splitdesc;
+		splitblock->prevoffset = xcf_get_offset(desc);
+		SET_SENTINEL(splitblock);
+		xcf_unmap_block(block, KM_USER0);
+
+		xcf_insert_block(pool, splitdesc);
+	}
+
+	desc->size = sizeleft + sizeof(struct xcf_blkhdr);
+
+	/* ensure the changes to desc are written before a potential
+	 read in xcf_get_alloc_size() since it does not aquire a
+	 lock */
+	wmb();
+
+	spin_unlock(&pool->lock);
+	return first;
+
+return_blocks:
+	desc = first;
+	while (desc) {
+		next = desc->next;
+		xcf_insert_block(pool, desc);
+		desc = next;
+	}
+	spin_unlock(&pool->lock);
+	return NULL;
+}
+
+enum xcf_op {
+	XCFMOP_READ,
+	XCFMOP_WRITE
+};
+
+static int access_allocation(void *handle, char *buf, enum xcf_op op)
+{
+	struct xcf_blkdesc *desc;
+	int count, offset;
+	char *block;
+
+	desc = handle;
+	count = XCF_MAX_BLOCKS_PER_ALLOC;
+	offset = 0;
+	while (desc && count--) {
+		BUG_ON(!xcf_is_used(desc));
+		BUG_ON(offset > MAX_ALLOC_SIZE);
+
+		block = xcf_map_block(desc, KM_USER0);
+		if (op == XCFMOP_WRITE)
+			memcpy(block + sizeof(struct xcf_blkhdr),
+				buf + offset,
+				desc->size - sizeof(struct xcf_blkhdr));
+		else /* XCFMOP_READ */
+			memcpy(buf + offset,
+				block + sizeof(struct xcf_blkhdr),
+				desc->size - sizeof(struct xcf_blkhdr));
+		xcf_unmap_block((struct xcf_blkhdr *)block, KM_USER0);
+
+		offset += desc->size - sizeof(struct xcf_blkhdr);
+		desc = desc->next;
+	}
+
+	BUG_ON(desc);
+
+	return 0;
+}
+
+/* write data from buf into allocation */
+int xcf_write(struct xcf_handle *handle, void *buf)
+{
+	return access_allocation(handle, buf, XCFMOP_WRITE);
+}
+
+/* read data from allocation into buf */
+int xcf_read(struct xcf_handle *handle, void *buf)
+{
+	return access_allocation(handle, buf, XCFMOP_READ);
+}
+
+/* free an allocation */
+void xcf_free(struct xcf_pool *pool, struct xcf_handle *handle)
+{
+	struct xcf_blkdesc *desc, *nextdesc;
+	int count;
+
+	spin_lock(&pool->lock);
+
+	desc = (struct xcf_blkdesc *)handle;
+	count = XCF_MAX_BLOCKS_PER_ALLOC;
+	while (desc && count--) {
+		nextdesc = desc->next;
+		BUG_ON(xcf_is_free(desc));
+		xcf_set_flags(desc, XCF_BLOCK_FREE);
+		desc->size = xcf_align_to_block(desc->size);
+		/* xcf_merge_free_block may merge with a previous block which
+		 * will cause desc to change */
+		desc = xcf_merge_free_block(pool, desc);
+		xcf_insert_block(pool, desc);
+		desc = nextdesc;
+	}
+
+	BUG_ON(desc);
+
+	/* check and possibly decrease (free) pool's page reserves */
+	xcf_decrease_pool(pool);
+
+	spin_unlock(&pool->lock);
+}
+
+/* create an xcfmalloc memory pool */
+struct xcf_pool *xcf_create_pool(gfp_t flags)
+{
+	struct xcf_pool *pool = NULL;
+
+	if (!xcf_desc_cache)
+		xcf_desc_cache = kmem_cache_create("xcf_desc_cache",
+			sizeof(struct xcf_blkdesc), 0, 0, NULL);
+
+	if (!xcf_desc_cache)
+		goto out;
+
+	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
+	if (!pool)
+		goto out;
+
+	spin_lock_init(&pool->lock);
+
+	xcf_increase_pool(pool, flags);
+
+out:
+	return pool;
+}
+
+/* destroy an xcfmalloc memory pool */
+void xcf_destroy_pool(struct xcf_pool *pool)
+{
+	struct xcf_blkdesc *desc, *nextdesc;
+
+	/* free reserved pages */
+	desc = pool->freelists[XCF_RESERVED_INDEX];
+	while (desc) {
+		nextdesc = desc->next;
+		__free_page(desc->page);
+		xcf_free_desc(pool, desc);
+		desc = nextdesc;
+	}
+
+	kfree(pool);
+}
+
+/* get size of allocation associated with handle */
+int xcf_get_alloc_size(struct xcf_handle *handle)
+{
+	struct xcf_blkdesc *desc;
+	int count, size = 0;
+
+	if (!handle)
+		goto out;
+
+	/* ensure the changes to desc by xcf_malloc() are written before
+	 we access here since we don't acquire a lock */
+	rmb();
+
+	desc = (struct xcf_blkdesc *)handle;
+	count = XCF_MAX_BLOCKS_PER_ALLOC;
+	while (desc && count--) {
+		BUG_ON(!xcf_is_used(desc));
+		size += desc->size - sizeof(struct xcf_blkhdr);
+		desc = desc->next;
+	}
+
+out:
+	return size;
+}
+
+/* get total number of pages in use by pool not including the reserved pages */
+u64 xcf_get_total_size_bytes(struct xcf_pool *pool)
+{
+	u64 ret;
+	spin_lock(&pool->lock);
+	ret = pool->page_count - pool->reserve_count;
+	spin_unlock(&pool->lock);
+	return ret << PAGE_SHIFT;
+}
+
+/* get number of descriptors in use by pool not including the descriptors for
+ * reserved pages */
+int xcf_get_desc_count(struct xcf_pool *pool)
+{
+	int ret;
+	spin_lock(&pool->lock);
+	ret = pool->desc_count - pool->reserve_count;
+	spin_unlock(&pool->lock);
+	return ret;
+}
+
diff --git a/drivers/staging/zcache/xcfmalloc.h b/drivers/staging/zcache/xcfmalloc.h
new file mode 100644
index 0000000..38e2df9
--- /dev/null
+++ b/drivers/staging/zcache/xcfmalloc.h
@@ -0,0 +1,29 @@
+/* xcfmalloc.h */
+
+#ifndef _XCFMALLOC_H_
+#define _XCFMALLOC_H_
+
+#include <linux/kernel.h>
+#include <linux/types.h>
+
+struct xcf_pool;
+struct xcf_handle {
+	void *desc;
+};
+
+void *xcf_malloc(struct xcf_pool *pool, int size, gfp_t flags);
+void xcf_free(struct xcf_pool *pool, struct xcf_handle *handle);
+
+int xcf_write(struct xcf_handle *handle, void *buf);
+int xcf_read(struct xcf_handle *handle, void *buf);
+
+struct xcf_pool *xcf_create_pool(gfp_t flags);
+void xcf_destroy_pool(struct xcf_pool *pool);
+
+int xcf_get_alloc_size(struct xcf_handle *handle);
+
+u64 xcf_get_total_size_bytes(struct xcf_pool *pool);
+int xcf_get_desc_count(struct xcf_pool *pool);
+
+#endif /* _XCFMALLOC_H_ */
+
-- 
1.7.4.1

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