diff --git a/drivers/staging/zcache/zcache.c b/drivers/staging/zcache/zcache.c
new file mode 100644
index 000000000000..61be8498fb06
--- /dev/null
+++ b/drivers/staging/zcache/zcache.c
@@ -0,0 +1,1657 @@
+/*
+ * zcache.c
+ *
+ * Copyright (c) 2010,2011, Dan Magenheimer, Oracle Corp.
+ * Copyright (c) 2010,2011, Nitin Gupta
+ *
+ * Zcache provides an in-kernel "host implementation" for transcendent memory
+ * and, thus indirectly, for cleancache and frontswap.  Zcache includes two
+ * page-accessible memory [1] interfaces, both utilizing lzo1x compression:
+ * 1) "compression buddies" ("zbud") is used for ephemeral pages
+ * 2) xvmalloc is used for persistent pages.
+ * Xvmalloc (based on the TLSF allocator) has very low fragmentation
+ * so maximizes space efficiency, while zbud allows pairs (and potentially,
+ * in the future, more than a pair of) compressed pages to be closely linked
+ * so that reclaiming can be done via the kernel's physical-page-oriented
+ * "shrinker" interface.
+ *
+ * [1] For a definition of page-accessible memory (aka PAM), see:
+ *   http://marc.info/?l=linux-mm&m=127811271605009
+ */
+
+#include <linux/cpu.h>
+#include <linux/highmem.h>
+#include <linux/list.h>
+#include <linux/lzo.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include <linux/atomic.h>
+#include "tmem.h"
+
+#include "../zram/xvmalloc.h" /* if built in drivers/staging */
+
+#if (!defined(CONFIG_CLEANCACHE) && !defined(CONFIG_FRONTSWAP))
+#error "zcache is useless without CONFIG_CLEANCACHE or CONFIG_FRONTSWAP"
+#endif
+#ifdef CONFIG_CLEANCACHE
+#include <linux/cleancache.h>
+#endif
+#ifdef CONFIG_FRONTSWAP
+#include <linux/frontswap.h>
+#endif
+
+#if 0
+/* this is more aggressive but may cause other problems? */
+#define ZCACHE_GFP_MASK	(GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN)
+#else
+#define ZCACHE_GFP_MASK \
+	(__GFP_FS | __GFP_NORETRY | __GFP_NOWARN | __GFP_NOMEMALLOC)
+#endif
+
+/**********
+ * Compression buddies ("zbud") provides for packing two (or, possibly
+ * in the future, more) compressed ephemeral pages into a single "raw"
+ * (physical) page and tracking them with data structures so that
+ * the raw pages can be easily reclaimed.
+ *
+ * A zbud page ("zbpg") is an aligned page containing a list_head,
+ * a lock, and two "zbud headers".  The remainder of the physical
+ * page is divided up into aligned 64-byte "chunks" which contain
+ * the compressed data for zero, one, or two zbuds.  Each zbpg
+ * resides on: (1) an "unused list" if it has no zbuds; (2) a
+ * "buddied" list if it is fully populated  with two zbuds; or
+ * (3) one of PAGE_SIZE/64 "unbuddied" lists indexed by how many chunks
+ * the one unbuddied zbud uses.  The data inside a zbpg cannot be
+ * read or written unless the zbpg's lock is held.
+ */
+
+#define ZBH_SENTINEL  0x43214321
+#define ZBPG_SENTINEL  0xdeadbeef
+
+#define ZBUD_MAX_BUDS 2
+
+struct zbud_hdr {
+	uint32_t pool_id;
+	struct tmem_oid oid;
+	uint32_t index;
+	uint16_t size; /* compressed size in bytes, zero means unused */
+	DECL_SENTINEL
+};
+
+struct zbud_page {
+	struct list_head bud_list;
+	spinlock_t lock;
+	struct zbud_hdr buddy[ZBUD_MAX_BUDS];
+	DECL_SENTINEL
+	/* followed by NUM_CHUNK aligned CHUNK_SIZE-byte chunks */
+};
+
+#define CHUNK_SHIFT	6
+#define CHUNK_SIZE	(1 << CHUNK_SHIFT)
+#define CHUNK_MASK	(~(CHUNK_SIZE-1))
+#define NCHUNKS		(((PAGE_SIZE - sizeof(struct zbud_page)) & \
+				CHUNK_MASK) >> CHUNK_SHIFT)
+#define MAX_CHUNK	(NCHUNKS-1)
+
+static struct {
+	struct list_head list;
+	unsigned count;
+} zbud_unbuddied[NCHUNKS];
+/* list N contains pages with N chunks USED and NCHUNKS-N unused */
+/* element 0 is never used but optimizing that isn't worth it */
+static unsigned long zbud_cumul_chunk_counts[NCHUNKS];
+
+struct list_head zbud_buddied_list;
+static unsigned long zcache_zbud_buddied_count;
+
+/* protects the buddied list and all unbuddied lists */
+static DEFINE_SPINLOCK(zbud_budlists_spinlock);
+
+static LIST_HEAD(zbpg_unused_list);
+static unsigned long zcache_zbpg_unused_list_count;
+
+/* protects the unused page list */
+static DEFINE_SPINLOCK(zbpg_unused_list_spinlock);
+
+static atomic_t zcache_zbud_curr_raw_pages;
+static atomic_t zcache_zbud_curr_zpages;
+static unsigned long zcache_zbud_curr_zbytes;
+static unsigned long zcache_zbud_cumul_zpages;
+static unsigned long zcache_zbud_cumul_zbytes;
+static unsigned long zcache_compress_poor;
+
+/* forward references */
+static void *zcache_get_free_page(void);
+static void zcache_free_page(void *p);
+
+/*
+ * zbud helper functions
+ */
+
+static inline unsigned zbud_max_buddy_size(void)
+{
+	return MAX_CHUNK << CHUNK_SHIFT;
+}
+
+static inline unsigned zbud_size_to_chunks(unsigned size)
+{
+	BUG_ON(size == 0 || size > zbud_max_buddy_size());
+	return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
+}
+
+static inline int zbud_budnum(struct zbud_hdr *zh)
+{
+	unsigned offset = (unsigned long)zh & (PAGE_SIZE - 1);
+	struct zbud_page *zbpg = NULL;
+	unsigned budnum = -1U;
+	int i;
+
+	for (i = 0; i < ZBUD_MAX_BUDS; i++)
+		if (offset == offsetof(typeof(*zbpg), buddy[i])) {
+			budnum = i;
+			break;
+		}
+	BUG_ON(budnum == -1U);
+	return budnum;
+}
+
+static char *zbud_data(struct zbud_hdr *zh, unsigned size)
+{
+	struct zbud_page *zbpg;
+	char *p;
+	unsigned budnum;
+
+	ASSERT_SENTINEL(zh, ZBH);
+	budnum = zbud_budnum(zh);
+	BUG_ON(size == 0 || size > zbud_max_buddy_size());
+	zbpg = container_of(zh, struct zbud_page, buddy[budnum]);
+	ASSERT_SPINLOCK(&zbpg->lock);
+	p = (char *)zbpg;
+	if (budnum == 0)
+		p += ((sizeof(struct zbud_page) + CHUNK_SIZE - 1) &
+							CHUNK_MASK);
+	else if (budnum == 1)
+		p += PAGE_SIZE - ((size + CHUNK_SIZE - 1) & CHUNK_MASK);
+	return p;
+}
+
+/*
+ * zbud raw page management
+ */
+
+static struct zbud_page *zbud_alloc_raw_page(void)
+{
+	struct zbud_page *zbpg = NULL;
+	struct zbud_hdr *zh0, *zh1;
+	bool recycled = 0;
+
+	/* if any pages on the zbpg list, use one */
+	spin_lock(&zbpg_unused_list_spinlock);
+	if (!list_empty(&zbpg_unused_list)) {
+		zbpg = list_first_entry(&zbpg_unused_list,
+				struct zbud_page, bud_list);
+		list_del_init(&zbpg->bud_list);
+		zcache_zbpg_unused_list_count--;
+		recycled = 1;
+	}
+	spin_unlock(&zbpg_unused_list_spinlock);
+	if (zbpg == NULL)
+		/* none on zbpg list, try to get a kernel page */
+		zbpg = zcache_get_free_page();
+	if (likely(zbpg != NULL)) {
+		INIT_LIST_HEAD(&zbpg->bud_list);
+		zh0 = &zbpg->buddy[0]; zh1 = &zbpg->buddy[1];
+		spin_lock_init(&zbpg->lock);
+		if (recycled) {
+			ASSERT_INVERTED_SENTINEL(zbpg, ZBPG);
+			SET_SENTINEL(zbpg, ZBPG);
+			BUG_ON(zh0->size != 0 || tmem_oid_valid(&zh0->oid));
+			BUG_ON(zh1->size != 0 || tmem_oid_valid(&zh1->oid));
+		} else {
+			atomic_inc(&zcache_zbud_curr_raw_pages);
+			INIT_LIST_HEAD(&zbpg->bud_list);
+			SET_SENTINEL(zbpg, ZBPG);
+			zh0->size = 0; zh1->size = 0;
+			tmem_oid_set_invalid(&zh0->oid);
+			tmem_oid_set_invalid(&zh1->oid);
+		}
+	}
+	return zbpg;
+}
+
+static void zbud_free_raw_page(struct zbud_page *zbpg)
+{
+	struct zbud_hdr *zh0 = &zbpg->buddy[0], *zh1 = &zbpg->buddy[1];
+
+	ASSERT_SENTINEL(zbpg, ZBPG);
+	BUG_ON(!list_empty(&zbpg->bud_list));
+	ASSERT_SPINLOCK(&zbpg->lock);
+	BUG_ON(zh0->size != 0 || tmem_oid_valid(&zh0->oid));
+	BUG_ON(zh1->size != 0 || tmem_oid_valid(&zh1->oid));
+	INVERT_SENTINEL(zbpg, ZBPG);
+	spin_unlock(&zbpg->lock);
+	spin_lock(&zbpg_unused_list_spinlock);
+	list_add(&zbpg->bud_list, &zbpg_unused_list);
+	zcache_zbpg_unused_list_count++;
+	spin_unlock(&zbpg_unused_list_spinlock);
+}
+
+/*
+ * core zbud handling routines
+ */
+
+static unsigned zbud_free(struct zbud_hdr *zh)
+{
+	unsigned size;
+
+	ASSERT_SENTINEL(zh, ZBH);
+	BUG_ON(!tmem_oid_valid(&zh->oid));
+	size = zh->size;
+	BUG_ON(zh->size == 0 || zh->size > zbud_max_buddy_size());
+	zh->size = 0;
+	tmem_oid_set_invalid(&zh->oid);
+	INVERT_SENTINEL(zh, ZBH);
+	zcache_zbud_curr_zbytes -= size;
+	atomic_dec(&zcache_zbud_curr_zpages);
+	return size;
+}
+
+static void zbud_free_and_delist(struct zbud_hdr *zh)
+{
+	unsigned chunks;
+	struct zbud_hdr *zh_other;
+	unsigned budnum = zbud_budnum(zh), size;
+	struct zbud_page *zbpg =
+		container_of(zh, struct zbud_page, buddy[budnum]);
+
+	spin_lock(&zbpg->lock);
+	if (list_empty(&zbpg->bud_list)) {
+		/* ignore zombie page... see zbud_evict_pages() */
+		spin_unlock(&zbpg->lock);
+		return;
+	}
+	size = zbud_free(zh);
+	ASSERT_SPINLOCK(&zbpg->lock);
+	zh_other = &zbpg->buddy[(budnum == 0) ? 1 : 0];
+	if (zh_other->size == 0) { /* was unbuddied: unlist and free */
+		chunks = zbud_size_to_chunks(size) ;
+		spin_lock(&zbud_budlists_spinlock);
+		BUG_ON(list_empty(&zbud_unbuddied[chunks].list));
+		list_del_init(&zbpg->bud_list);
+		zbud_unbuddied[chunks].count--;
+		spin_unlock(&zbud_budlists_spinlock);
+		zbud_free_raw_page(zbpg);
+	} else { /* was buddied: move remaining buddy to unbuddied list */
+		chunks = zbud_size_to_chunks(zh_other->size) ;
+		spin_lock(&zbud_budlists_spinlock);
+		list_del_init(&zbpg->bud_list);
+		zcache_zbud_buddied_count--;
+		list_add_tail(&zbpg->bud_list, &zbud_unbuddied[chunks].list);
+		zbud_unbuddied[chunks].count++;
+		spin_unlock(&zbud_budlists_spinlock);
+		spin_unlock(&zbpg->lock);
+	}
+}
+
+static struct zbud_hdr *zbud_create(uint32_t pool_id, struct tmem_oid *oid,
+					uint32_t index, struct page *page,
+					void *cdata, unsigned size)
+{
+	struct zbud_hdr *zh0, *zh1, *zh = NULL;
+	struct zbud_page *zbpg = NULL, *ztmp;
+	unsigned nchunks;
+	char *to;
+	int i, found_good_buddy = 0;
+
+	nchunks = zbud_size_to_chunks(size) ;
+	for (i = MAX_CHUNK - nchunks + 1; i > 0; i--) {
+		spin_lock(&zbud_budlists_spinlock);
+		if (!list_empty(&zbud_unbuddied[i].list)) {
+			list_for_each_entry_safe(zbpg, ztmp,
+				    &zbud_unbuddied[i].list, bud_list) {
+				if (spin_trylock(&zbpg->lock)) {
+					found_good_buddy = i;
+					goto found_unbuddied;
+				}
+			}
+		}
+		spin_unlock(&zbud_budlists_spinlock);
+	}
+	/* didn't find a good buddy, try allocating a new page */
+	zbpg = zbud_alloc_raw_page();
+	if (unlikely(zbpg == NULL))
+		goto out;
+	/* ok, have a page, now compress the data before taking locks */
+	spin_lock(&zbpg->lock);
+	spin_lock(&zbud_budlists_spinlock);
+	list_add_tail(&zbpg->bud_list, &zbud_unbuddied[nchunks].list);
+	zbud_unbuddied[nchunks].count++;
+	zh = &zbpg->buddy[0];
+	goto init_zh;
+
+found_unbuddied:
+	ASSERT_SPINLOCK(&zbpg->lock);
+	zh0 = &zbpg->buddy[0]; zh1 = &zbpg->buddy[1];
+	BUG_ON(!((zh0->size == 0) ^ (zh1->size == 0)));
+	if (zh0->size != 0) { /* buddy0 in use, buddy1 is vacant */
+		ASSERT_SENTINEL(zh0, ZBH);
+		zh = zh1;
+	} else if (zh1->size != 0) { /* buddy1 in use, buddy0 is vacant */
+		ASSERT_SENTINEL(zh1, ZBH);
+		zh = zh0;
+	} else
+		BUG();
+	list_del_init(&zbpg->bud_list);
+	zbud_unbuddied[found_good_buddy].count--;
+	list_add_tail(&zbpg->bud_list, &zbud_buddied_list);
+	zcache_zbud_buddied_count++;
+
+init_zh:
+	SET_SENTINEL(zh, ZBH);
+	zh->size = size;
+	zh->index = index;
+	zh->oid = *oid;
+	zh->pool_id = pool_id;
+	/* can wait to copy the data until the list locks are dropped */
+	spin_unlock(&zbud_budlists_spinlock);
+
+	to = zbud_data(zh, size);
+	memcpy(to, cdata, size);
+	spin_unlock(&zbpg->lock);
+	zbud_cumul_chunk_counts[nchunks]++;
+	atomic_inc(&zcache_zbud_curr_zpages);
+	zcache_zbud_cumul_zpages++;
+	zcache_zbud_curr_zbytes += size;
+	zcache_zbud_cumul_zbytes += size;
+out:
+	return zh;
+}
+
+static int zbud_decompress(struct page *page, struct zbud_hdr *zh)
+{
+	struct zbud_page *zbpg;
+	unsigned budnum = zbud_budnum(zh);
+	size_t out_len = PAGE_SIZE;
+	char *to_va, *from_va;
+	unsigned size;
+	int ret = 0;
+
+	zbpg = container_of(zh, struct zbud_page, buddy[budnum]);
+	spin_lock(&zbpg->lock);
+	if (list_empty(&zbpg->bud_list)) {
+		/* ignore zombie page... see zbud_evict_pages() */
+		ret = -EINVAL;
+		goto out;
+	}
+	ASSERT_SENTINEL(zh, ZBH);
+	BUG_ON(zh->size == 0 || zh->size > zbud_max_buddy_size());
+	to_va = kmap_atomic(page, KM_USER0);
+	size = zh->size;
+	from_va = zbud_data(zh, size);
+	ret = lzo1x_decompress_safe(from_va, size, to_va, &out_len);
+	BUG_ON(ret != LZO_E_OK);
+	BUG_ON(out_len != PAGE_SIZE);
+	kunmap_atomic(to_va, KM_USER0);
+out:
+	spin_unlock(&zbpg->lock);
+	return ret;
+}
+
+/*
+ * The following routines handle shrinking of ephemeral pages by evicting
+ * pages "least valuable" first.
+ */
+
+static unsigned long zcache_evicted_raw_pages;
+static unsigned long zcache_evicted_buddied_pages;
+static unsigned long zcache_evicted_unbuddied_pages;
+
+static struct tmem_pool *zcache_get_pool_by_id(uint32_t poolid);
+static void zcache_put_pool(struct tmem_pool *pool);
+
+/*
+ * Flush and free all zbuds in a zbpg, then free the pageframe
+ */
+static void zbud_evict_zbpg(struct zbud_page *zbpg)
+{
+	struct zbud_hdr *zh;
+	int i, j;
+	uint32_t pool_id[ZBUD_MAX_BUDS], index[ZBUD_MAX_BUDS];
+	struct tmem_oid oid[ZBUD_MAX_BUDS];
+	struct tmem_pool *pool;
+
+	ASSERT_SPINLOCK(&zbpg->lock);
+	BUG_ON(!list_empty(&zbpg->bud_list));
+	for (i = 0, j = 0; i < ZBUD_MAX_BUDS; i++) {
+		zh = &zbpg->buddy[i];
+		if (zh->size) {
+			pool_id[j] = zh->pool_id;
+			oid[j] = zh->oid;
+			index[j] = zh->index;
+			j++;
+			zbud_free(zh);
+		}
+	}
+	spin_unlock(&zbpg->lock);
+	for (i = 0; i < j; i++) {
+		pool = zcache_get_pool_by_id(pool_id[i]);
+		if (pool != NULL) {
+			tmem_flush_page(pool, &oid[i], index[i]);
+			zcache_put_pool(pool);
+		}
+	}
+	ASSERT_SENTINEL(zbpg, ZBPG);
+	spin_lock(&zbpg->lock);
+	zbud_free_raw_page(zbpg);
+}
+
+/*
+ * Free nr pages.  This code is funky because we want to hold the locks
+ * protecting various lists for as short a time as possible, and in some
+ * circumstances the list may change asynchronously when the list lock is
+ * not held.  In some cases we also trylock not only to avoid waiting on a
+ * page in use by another cpu, but also to avoid potential deadlock due to
+ * lock inversion.
+ */
+static void zbud_evict_pages(int nr)
+{
+	struct zbud_page *zbpg;
+	int i;
+
+	/* first try freeing any pages on unused list */
+retry_unused_list:
+	spin_lock_bh(&zbpg_unused_list_spinlock);
+	if (!list_empty(&zbpg_unused_list)) {
+		/* can't walk list here, since it may change when unlocked */
+		zbpg = list_first_entry(&zbpg_unused_list,
+				struct zbud_page, bud_list);
+		list_del_init(&zbpg->bud_list);
+		zcache_zbpg_unused_list_count--;
+		atomic_dec(&zcache_zbud_curr_raw_pages);
+		spin_unlock_bh(&zbpg_unused_list_spinlock);
+		zcache_free_page(zbpg);
+		zcache_evicted_raw_pages++;
+		if (--nr <= 0)
+			goto out;
+		goto retry_unused_list;
+	}
+	spin_unlock_bh(&zbpg_unused_list_spinlock);
+
+	/* now try freeing unbuddied pages, starting with least space avail */
+	for (i = 0; i < MAX_CHUNK; i++) {
+retry_unbud_list_i:
+		spin_lock_bh(&zbud_budlists_spinlock);
+		if (list_empty(&zbud_unbuddied[i].list)) {
+			spin_unlock_bh(&zbud_budlists_spinlock);
+			continue;
+		}
+		list_for_each_entry(zbpg, &zbud_unbuddied[i].list, bud_list) {
+			if (unlikely(!spin_trylock(&zbpg->lock)))
+				continue;
+			list_del_init(&zbpg->bud_list);
+			zbud_unbuddied[i].count--;
+			spin_unlock(&zbud_budlists_spinlock);
+			zcache_evicted_unbuddied_pages++;
+			/* want budlists unlocked when doing zbpg eviction */
+			zbud_evict_zbpg(zbpg);
+			local_bh_enable();
+			if (--nr <= 0)
+				goto out;
+			goto retry_unbud_list_i;
+		}
+		spin_unlock_bh(&zbud_budlists_spinlock);
+	}
+
+	/* as a last resort, free buddied pages */
+retry_bud_list:
+	spin_lock_bh(&zbud_budlists_spinlock);
+	if (list_empty(&zbud_buddied_list)) {
+		spin_unlock_bh(&zbud_budlists_spinlock);
+		goto out;
+	}
+	list_for_each_entry(zbpg, &zbud_buddied_list, bud_list) {
+		if (unlikely(!spin_trylock(&zbpg->lock)))
+			continue;
+		list_del_init(&zbpg->bud_list);
+		zcache_zbud_buddied_count--;
+		spin_unlock(&zbud_budlists_spinlock);
+		zcache_evicted_buddied_pages++;
+		/* want budlists unlocked when doing zbpg eviction */
+		zbud_evict_zbpg(zbpg);
+		local_bh_enable();
+		if (--nr <= 0)
+			goto out;
+		goto retry_bud_list;
+	}
+	spin_unlock_bh(&zbud_budlists_spinlock);
+out:
+	return;
+}
+
+static void zbud_init(void)
+{
+	int i;
+
+	INIT_LIST_HEAD(&zbud_buddied_list);
+	zcache_zbud_buddied_count = 0;
+	for (i = 0; i < NCHUNKS; i++) {
+		INIT_LIST_HEAD(&zbud_unbuddied[i].list);
+		zbud_unbuddied[i].count = 0;
+	}
+}
+
+#ifdef CONFIG_SYSFS
+/*
+ * These sysfs routines show a nice distribution of how many zbpg's are
+ * currently (and have ever been placed) in each unbuddied list.  It's fun
+ * to watch but can probably go away before final merge.
+ */
+static int zbud_show_unbuddied_list_counts(char *buf)
+{
+	int i;
+	char *p = buf;
+
+	for (i = 0; i < NCHUNKS - 1; i++)
+		p += sprintf(p, "%u ", zbud_unbuddied[i].count);
+	p += sprintf(p, "%d\n", zbud_unbuddied[i].count);
+	return p - buf;
+}
+
+static int zbud_show_cumul_chunk_counts(char *buf)
+{
+	unsigned long i, chunks = 0, total_chunks = 0, sum_total_chunks = 0;
+	unsigned long total_chunks_lte_21 = 0, total_chunks_lte_32 = 0;
+	unsigned long total_chunks_lte_42 = 0;
+	char *p = buf;
+
+	for (i = 0; i < NCHUNKS; i++) {
+		p += sprintf(p, "%lu ", zbud_cumul_chunk_counts[i]);
+		chunks += zbud_cumul_chunk_counts[i];
+		total_chunks += zbud_cumul_chunk_counts[i];
+		sum_total_chunks += i * zbud_cumul_chunk_counts[i];
+		if (i == 21)
+			total_chunks_lte_21 = total_chunks;
+		if (i == 32)
+			total_chunks_lte_32 = total_chunks;
+		if (i == 42)
+			total_chunks_lte_42 = total_chunks;
+	}
+	p += sprintf(p, "<=21:%lu <=32:%lu <=42:%lu, mean:%lu\n",
+		total_chunks_lte_21, total_chunks_lte_32, total_chunks_lte_42,
+		chunks == 0 ? 0 : sum_total_chunks / chunks);
+	return p - buf;
+}
+#endif
+
+/**********
+ * This "zv" PAM implementation combines the TLSF-based xvMalloc
+ * with lzo1x compression to maximize the amount of data that can
+ * be packed into a physical page.
+ *
+ * Zv represents a PAM page with the index and object (plus a "size" value
+ * necessary for decompression) immediately preceding the compressed data.
+ */
+
+#define ZVH_SENTINEL  0x43214321
+
+struct zv_hdr {
+	uint32_t pool_id;
+	struct tmem_oid oid;
+	uint32_t index;
+	DECL_SENTINEL
+};
+
+static const int zv_max_page_size = (PAGE_SIZE / 8) * 7;
+
+static struct zv_hdr *zv_create(struct xv_pool *xvpool, uint32_t pool_id,
+				struct tmem_oid *oid, uint32_t index,
+				void *cdata, unsigned clen)
+{
+	struct page *page;
+	struct zv_hdr *zv = NULL;
+	uint32_t offset;
+	int ret;
+
+	BUG_ON(!irqs_disabled());
+	ret = xv_malloc(xvpool, clen + sizeof(struct zv_hdr),
+			&page, &offset, ZCACHE_GFP_MASK);
+	if (unlikely(ret))
+		goto out;
+	zv = kmap_atomic(page, KM_USER0) + offset;
+	zv->index = index;
+	zv->oid = *oid;
+	zv->pool_id = pool_id;
+	SET_SENTINEL(zv, ZVH);
+	memcpy((char *)zv + sizeof(struct zv_hdr), cdata, clen);
+	kunmap_atomic(zv, KM_USER0);
+out:
+	return zv;
+}
+
+static void zv_free(struct xv_pool *xvpool, struct zv_hdr *zv)
+{
+	unsigned long flags;
+	struct page *page;
+	uint32_t offset;
+	uint16_t size;
+
+	ASSERT_SENTINEL(zv, ZVH);
+	size = xv_get_object_size(zv) - sizeof(*zv);
+	BUG_ON(size == 0 || size > zv_max_page_size);
+	INVERT_SENTINEL(zv, ZVH);
+	page = virt_to_page(zv);
+	offset = (unsigned long)zv & ~PAGE_MASK;
+	local_irq_save(flags);
+	xv_free(xvpool, page, offset);
+	local_irq_restore(flags);
+}
+
+static void zv_decompress(struct page *page, struct zv_hdr *zv)
+{
+	size_t clen = PAGE_SIZE;
+	char *to_va;
+	unsigned size;
+	int ret;
+
+	ASSERT_SENTINEL(zv, ZVH);
+	size = xv_get_object_size(zv) - sizeof(*zv);
+	BUG_ON(size == 0 || size > zv_max_page_size);
+	to_va = kmap_atomic(page, KM_USER0);
+	ret = lzo1x_decompress_safe((char *)zv + sizeof(*zv),
+					size, to_va, &clen);
+	kunmap_atomic(to_va, KM_USER0);
+	BUG_ON(ret != LZO_E_OK);
+	BUG_ON(clen != PAGE_SIZE);
+}
+
+/*
+ * zcache core code starts here
+ */
+
+/* useful stats not collected by cleancache or frontswap */
+static unsigned long zcache_flush_total;
+static unsigned long zcache_flush_found;
+static unsigned long zcache_flobj_total;
+static unsigned long zcache_flobj_found;
+static unsigned long zcache_failed_eph_puts;
+static unsigned long zcache_failed_pers_puts;
+
+#define MAX_POOLS_PER_CLIENT 16
+
+static struct {
+	struct tmem_pool *tmem_pools[MAX_POOLS_PER_CLIENT];
+	struct xv_pool *xvpool;
+} zcache_client;
+
+/*
+ * Tmem operations assume the poolid implies the invoking client.
+ * Zcache only has one client (the kernel itself), so translate
+ * the poolid into the tmem_pool allocated for it.  A KVM version
+ * of zcache would have one client per guest and each client might
+ * have a poolid==N.
+ */
+static struct tmem_pool *zcache_get_pool_by_id(uint32_t poolid)
+{
+	struct tmem_pool *pool = NULL;
+
+	if (poolid >= 0) {
+		pool = zcache_client.tmem_pools[poolid];
+		if (pool != NULL)
+			atomic_inc(&pool->refcount);
+	}
+	return pool;
+}
+
+static void zcache_put_pool(struct tmem_pool *pool)
+{
+	if (pool != NULL)
+		atomic_dec(&pool->refcount);
+}
+
+/* counters for debugging */
+static unsigned long zcache_failed_get_free_pages;
+static unsigned long zcache_failed_alloc;
+static unsigned long zcache_put_to_flush;
+static unsigned long zcache_aborted_preload;
+static unsigned long zcache_aborted_shrink;
+
+/*
+ * Ensure that memory allocation requests in zcache don't result
+ * in direct reclaim requests via the shrinker, which would cause
+ * an infinite loop.  Maybe a GFP flag would be better?
+ */
+static DEFINE_SPINLOCK(zcache_direct_reclaim_lock);
+
+/*
+ * for now, used named slabs so can easily track usage; later can
+ * either just use kmalloc, or perhaps add a slab-like allocator
+ * to more carefully manage total memory utilization
+ */
+static struct kmem_cache *zcache_objnode_cache;
+static struct kmem_cache *zcache_obj_cache;
+static atomic_t zcache_curr_obj_count = ATOMIC_INIT(0);
+static unsigned long zcache_curr_obj_count_max;
+static atomic_t zcache_curr_objnode_count = ATOMIC_INIT(0);
+static unsigned long zcache_curr_objnode_count_max;
+
+/*
+ * to avoid memory allocation recursion (e.g. due to direct reclaim), we
+ * preload all necessary data structures so the hostops callbacks never
+ * actually do a malloc
+ */
+struct zcache_preload {
+	void *page;
+	struct tmem_obj *obj;
+	int nr;
+	struct tmem_objnode *objnodes[OBJNODE_TREE_MAX_PATH];
+};
+static DEFINE_PER_CPU(struct zcache_preload, zcache_preloads) = { 0, };
+
+static int zcache_do_preload(struct tmem_pool *pool)
+{
+	struct zcache_preload *kp;
+	struct tmem_objnode *objnode;
+	struct tmem_obj *obj;
+	void *page;
+	int ret = -ENOMEM;
+
+	if (unlikely(zcache_objnode_cache == NULL))
+		goto out;
+	if (unlikely(zcache_obj_cache == NULL))
+		goto out;
+	if (!spin_trylock(&zcache_direct_reclaim_lock)) {
+		zcache_aborted_preload++;
+		goto out;
+	}
+	preempt_disable();
+	kp = &__get_cpu_var(zcache_preloads);
+	while (kp->nr < ARRAY_SIZE(kp->objnodes)) {
+		preempt_enable_no_resched();
+		objnode = kmem_cache_alloc(zcache_objnode_cache,
+				ZCACHE_GFP_MASK);
+		if (unlikely(objnode == NULL)) {
+			zcache_failed_alloc++;
+			goto unlock_out;
+		}
+		preempt_disable();
+		kp = &__get_cpu_var(zcache_preloads);
+		if (kp->nr < ARRAY_SIZE(kp->objnodes))
+			kp->objnodes[kp->nr++] = objnode;
+		else
+			kmem_cache_free(zcache_objnode_cache, objnode);
+	}
+	preempt_enable_no_resched();
+	obj = kmem_cache_alloc(zcache_obj_cache, ZCACHE_GFP_MASK);
+	if (unlikely(obj == NULL)) {
+		zcache_failed_alloc++;
+		goto unlock_out;
+	}
+	page = (void *)__get_free_page(ZCACHE_GFP_MASK);
+	if (unlikely(page == NULL)) {
+		zcache_failed_get_free_pages++;
+		goto unlock_out;
+	}
+	preempt_disable();
+	kp = &__get_cpu_var(zcache_preloads);
+	if (kp->obj == NULL)
+		kp->obj = obj;
+	else
+		kmem_cache_free(zcache_obj_cache, obj);
+	if (kp->page == NULL)
+		kp->page = page;
+	else
+		free_page((unsigned long)page);
+	ret = 0;
+unlock_out:
+	spin_unlock(&zcache_direct_reclaim_lock);
+out:
+	return ret;
+}
+
+static void *zcache_get_free_page(void)
+{
+	struct zcache_preload *kp;
+	void *page;
+
+	kp = &__get_cpu_var(zcache_preloads);
+	page = kp->page;
+	BUG_ON(page == NULL);
+	kp->page = NULL;
+	return page;
+}
+
+static void zcache_free_page(void *p)
+{
+	free_page((unsigned long)p);
+}
+
+/*
+ * zcache implementation for tmem host ops
+ */
+
+static struct tmem_objnode *zcache_objnode_alloc(struct tmem_pool *pool)
+{
+	struct tmem_objnode *objnode = NULL;
+	unsigned long count;
+	struct zcache_preload *kp;
+
+	kp = &__get_cpu_var(zcache_preloads);
+	if (kp->nr <= 0)
+		goto out;
+	objnode = kp->objnodes[kp->nr - 1];
+	BUG_ON(objnode == NULL);
+	kp->objnodes[kp->nr - 1] = NULL;
+	kp->nr--;
+	count = atomic_inc_return(&zcache_curr_objnode_count);
+	if (count > zcache_curr_objnode_count_max)
+		zcache_curr_objnode_count_max = count;
+out:
+	return objnode;
+}
+
+static void zcache_objnode_free(struct tmem_objnode *objnode,
+					struct tmem_pool *pool)
+{
+	atomic_dec(&zcache_curr_objnode_count);
+	BUG_ON(atomic_read(&zcache_curr_objnode_count) < 0);
+	kmem_cache_free(zcache_objnode_cache, objnode);
+}
+
+static struct tmem_obj *zcache_obj_alloc(struct tmem_pool *pool)
+{
+	struct tmem_obj *obj = NULL;
+	unsigned long count;
+	struct zcache_preload *kp;
+
+	kp = &__get_cpu_var(zcache_preloads);
+	obj = kp->obj;
+	BUG_ON(obj == NULL);
+	kp->obj = NULL;
+	count = atomic_inc_return(&zcache_curr_obj_count);
+	if (count > zcache_curr_obj_count_max)
+		zcache_curr_obj_count_max = count;
+	return obj;
+}
+
+static void zcache_obj_free(struct tmem_obj *obj, struct tmem_pool *pool)
+{
+	atomic_dec(&zcache_curr_obj_count);
+	BUG_ON(atomic_read(&zcache_curr_obj_count) < 0);
+	kmem_cache_free(zcache_obj_cache, obj);
+}
+
+static struct tmem_hostops zcache_hostops = {
+	.obj_alloc = zcache_obj_alloc,
+	.obj_free = zcache_obj_free,
+	.objnode_alloc = zcache_objnode_alloc,
+	.objnode_free = zcache_objnode_free,
+};
+
+/*
+ * zcache implementations for PAM page descriptor ops
+ */
+
+static atomic_t zcache_curr_eph_pampd_count = ATOMIC_INIT(0);
+static unsigned long zcache_curr_eph_pampd_count_max;
+static atomic_t zcache_curr_pers_pampd_count = ATOMIC_INIT(0);
+static unsigned long zcache_curr_pers_pampd_count_max;
+
+/* forward reference */
+static int zcache_compress(struct page *from, void **out_va, size_t *out_len);
+
+static void *zcache_pampd_create(struct tmem_pool *pool, struct tmem_oid *oid,
+				 uint32_t index, struct page *page)
+{
+	void *pampd = NULL, *cdata;
+	size_t clen;
+	int ret;
+	bool ephemeral = is_ephemeral(pool);
+	unsigned long count;
+
+	if (ephemeral) {
+		ret = zcache_compress(page, &cdata, &clen);
+		if (ret == 0)
+
+			goto out;
+		if (clen == 0 || clen > zbud_max_buddy_size()) {
+			zcache_compress_poor++;
+			goto out;
+		}
+		pampd = (void *)zbud_create(pool->pool_id, oid, index,
+						page, cdata, clen);
+		if (pampd != NULL) {
+			count = atomic_inc_return(&zcache_curr_eph_pampd_count);
+			if (count > zcache_curr_eph_pampd_count_max)
+				zcache_curr_eph_pampd_count_max = count;
+		}
+	} else {
+		/*
+		 * FIXME: This is all the "policy" there is for now.
+		 * 3/4 totpages should allow ~37% of RAM to be filled with
+		 * compressed frontswap pages
+		 */
+		if (atomic_read(&zcache_curr_pers_pampd_count) >
+							3 * totalram_pages / 4)
+			goto out;
+		ret = zcache_compress(page, &cdata, &clen);
+		if (ret == 0)
+			goto out;
+		if (clen > zv_max_page_size) {
+			zcache_compress_poor++;
+			goto out;
+		}
+		pampd = (void *)zv_create(zcache_client.xvpool, pool->pool_id,
+						oid, index, cdata, clen);
+		if (pampd == NULL)
+			goto out;
+		count = atomic_inc_return(&zcache_curr_pers_pampd_count);
+		if (count > zcache_curr_pers_pampd_count_max)
+			zcache_curr_pers_pampd_count_max = count;
+	}
+out:
+	return pampd;
+}
+
+/*
+ * fill the pageframe corresponding to the struct page with the data
+ * from the passed pampd
+ */
+static int zcache_pampd_get_data(struct page *page, void *pampd,
+						struct tmem_pool *pool)
+{
+	int ret = 0;
+
+	if (is_ephemeral(pool))
+		ret = zbud_decompress(page, pampd);
+	else
+		zv_decompress(page, pampd);
+	return ret;
+}
+
+/*
+ * free the pampd and remove it from any zcache lists
+ * pampd must no longer be pointed to from any tmem data structures!
+ */
+static void zcache_pampd_free(void *pampd, struct tmem_pool *pool)
+{
+	if (is_ephemeral(pool)) {
+		zbud_free_and_delist((struct zbud_hdr *)pampd);
+		atomic_dec(&zcache_curr_eph_pampd_count);
+		BUG_ON(atomic_read(&zcache_curr_eph_pampd_count) < 0);
+	} else {
+		zv_free(zcache_client.xvpool, (struct zv_hdr *)pampd);
+		atomic_dec(&zcache_curr_pers_pampd_count);
+		BUG_ON(atomic_read(&zcache_curr_pers_pampd_count) < 0);
+	}
+}
+
+static struct tmem_pamops zcache_pamops = {
+	.create = zcache_pampd_create,
+	.get_data = zcache_pampd_get_data,
+	.free = zcache_pampd_free,
+};
+
+/*
+ * zcache compression/decompression and related per-cpu stuff
+ */
+
+#define LZO_WORKMEM_BYTES LZO1X_1_MEM_COMPRESS
+#define LZO_DSTMEM_PAGE_ORDER 1
+static DEFINE_PER_CPU(unsigned char *, zcache_workmem);
+static DEFINE_PER_CPU(unsigned char *, zcache_dstmem);
+
+static int zcache_compress(struct page *from, void **out_va, size_t *out_len)
+{
+	int ret = 0;
+	unsigned char *dmem = __get_cpu_var(zcache_dstmem);
+	unsigned char *wmem = __get_cpu_var(zcache_workmem);
+	char *from_va;
+
+	BUG_ON(!irqs_disabled());
+	if (unlikely(dmem == NULL || wmem == NULL))
+		goto out;  /* no buffer, so can't compress */
+	from_va = kmap_atomic(from, KM_USER0);
+	mb();
+	ret = lzo1x_1_compress(from_va, PAGE_SIZE, dmem, out_len, wmem);
+	BUG_ON(ret != LZO_E_OK);
+	*out_va = dmem;
+	kunmap_atomic(from_va, KM_USER0);
+	ret = 1;
+out:
+	return ret;
+}
+
+
+static int zcache_cpu_notifier(struct notifier_block *nb,
+				unsigned long action, void *pcpu)
+{
+	int cpu = (long)pcpu;
+	struct zcache_preload *kp;
+
+	switch (action) {
+	case CPU_UP_PREPARE:
+		per_cpu(zcache_dstmem, cpu) = (void *)__get_free_pages(
+			GFP_KERNEL | __GFP_REPEAT,
+			LZO_DSTMEM_PAGE_ORDER),
+		per_cpu(zcache_workmem, cpu) =
+			kzalloc(LZO1X_MEM_COMPRESS,
+				GFP_KERNEL | __GFP_REPEAT);
+		break;
+	case CPU_DEAD:
+	case CPU_UP_CANCELED:
+		free_pages((unsigned long)per_cpu(zcache_dstmem, cpu),
+				LZO_DSTMEM_PAGE_ORDER);
+		per_cpu(zcache_dstmem, cpu) = NULL;
+		kfree(per_cpu(zcache_workmem, cpu));
+		per_cpu(zcache_workmem, cpu) = NULL;
+		kp = &per_cpu(zcache_preloads, cpu);
+		while (kp->nr) {
+			kmem_cache_free(zcache_objnode_cache,
+					kp->objnodes[kp->nr - 1]);
+			kp->objnodes[kp->nr - 1] = NULL;
+			kp->nr--;
+		}
+		kmem_cache_free(zcache_obj_cache, kp->obj);
+		free_page((unsigned long)kp->page);
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block zcache_cpu_notifier_block = {
+	.notifier_call = zcache_cpu_notifier
+};
+
+#ifdef CONFIG_SYSFS
+#define ZCACHE_SYSFS_RO(_name) \
+	static ssize_t zcache_##_name##_show(struct kobject *kobj, \
+				struct kobj_attribute *attr, char *buf) \
+	{ \
+		return sprintf(buf, "%lu\n", zcache_##_name); \
+	} \
+	static struct kobj_attribute zcache_##_name##_attr = { \
+		.attr = { .name = __stringify(_name), .mode = 0444 }, \
+		.show = zcache_##_name##_show, \
+	}
+
+#define ZCACHE_SYSFS_RO_ATOMIC(_name) \
+	static ssize_t zcache_##_name##_show(struct kobject *kobj, \
+				struct kobj_attribute *attr, char *buf) \
+	{ \
+	    return sprintf(buf, "%d\n", atomic_read(&zcache_##_name)); \
+	} \
+	static struct kobj_attribute zcache_##_name##_attr = { \
+		.attr = { .name = __stringify(_name), .mode = 0444 }, \
+		.show = zcache_##_name##_show, \
+	}
+
+#define ZCACHE_SYSFS_RO_CUSTOM(_name, _func) \
+	static ssize_t zcache_##_name##_show(struct kobject *kobj, \
+				struct kobj_attribute *attr, char *buf) \
+	{ \
+	    return _func(buf); \
+	} \
+	static struct kobj_attribute zcache_##_name##_attr = { \
+		.attr = { .name = __stringify(_name), .mode = 0444 }, \
+		.show = zcache_##_name##_show, \
+	}
+
+ZCACHE_SYSFS_RO(curr_obj_count_max);
+ZCACHE_SYSFS_RO(curr_objnode_count_max);
+ZCACHE_SYSFS_RO(flush_total);
+ZCACHE_SYSFS_RO(flush_found);
+ZCACHE_SYSFS_RO(flobj_total);
+ZCACHE_SYSFS_RO(flobj_found);
+ZCACHE_SYSFS_RO(failed_eph_puts);
+ZCACHE_SYSFS_RO(failed_pers_puts);
+ZCACHE_SYSFS_RO(zbud_curr_zbytes);
+ZCACHE_SYSFS_RO(zbud_cumul_zpages);
+ZCACHE_SYSFS_RO(zbud_cumul_zbytes);
+ZCACHE_SYSFS_RO(zbud_buddied_count);
+ZCACHE_SYSFS_RO(zbpg_unused_list_count);
+ZCACHE_SYSFS_RO(evicted_raw_pages);
+ZCACHE_SYSFS_RO(evicted_unbuddied_pages);
+ZCACHE_SYSFS_RO(evicted_buddied_pages);
+ZCACHE_SYSFS_RO(failed_get_free_pages);
+ZCACHE_SYSFS_RO(failed_alloc);
+ZCACHE_SYSFS_RO(put_to_flush);
+ZCACHE_SYSFS_RO(aborted_preload);
+ZCACHE_SYSFS_RO(aborted_shrink);
+ZCACHE_SYSFS_RO(compress_poor);
+ZCACHE_SYSFS_RO_ATOMIC(zbud_curr_raw_pages);
+ZCACHE_SYSFS_RO_ATOMIC(zbud_curr_zpages);
+ZCACHE_SYSFS_RO_ATOMIC(curr_obj_count);
+ZCACHE_SYSFS_RO_ATOMIC(curr_objnode_count);
+ZCACHE_SYSFS_RO_CUSTOM(zbud_unbuddied_list_counts,
+			zbud_show_unbuddied_list_counts);
+ZCACHE_SYSFS_RO_CUSTOM(zbud_cumul_chunk_counts,
+			zbud_show_cumul_chunk_counts);
+
+static struct attribute *zcache_attrs[] = {
+	&zcache_curr_obj_count_attr.attr,
+	&zcache_curr_obj_count_max_attr.attr,
+	&zcache_curr_objnode_count_attr.attr,
+	&zcache_curr_objnode_count_max_attr.attr,
+	&zcache_flush_total_attr.attr,
+	&zcache_flobj_total_attr.attr,
+	&zcache_flush_found_attr.attr,
+	&zcache_flobj_found_attr.attr,
+	&zcache_failed_eph_puts_attr.attr,
+	&zcache_failed_pers_puts_attr.attr,
+	&zcache_compress_poor_attr.attr,
+	&zcache_zbud_curr_raw_pages_attr.attr,
+	&zcache_zbud_curr_zpages_attr.attr,
+	&zcache_zbud_curr_zbytes_attr.attr,
+	&zcache_zbud_cumul_zpages_attr.attr,
+	&zcache_zbud_cumul_zbytes_attr.attr,
+	&zcache_zbud_buddied_count_attr.attr,
+	&zcache_zbpg_unused_list_count_attr.attr,
+	&zcache_evicted_raw_pages_attr.attr,
+	&zcache_evicted_unbuddied_pages_attr.attr,
+	&zcache_evicted_buddied_pages_attr.attr,
+	&zcache_failed_get_free_pages_attr.attr,
+	&zcache_failed_alloc_attr.attr,
+	&zcache_put_to_flush_attr.attr,
+	&zcache_aborted_preload_attr.attr,
+	&zcache_aborted_shrink_attr.attr,
+	&zcache_zbud_unbuddied_list_counts_attr.attr,
+	&zcache_zbud_cumul_chunk_counts_attr.attr,
+	NULL,
+};
+
+static struct attribute_group zcache_attr_group = {
+	.attrs = zcache_attrs,
+	.name = "zcache",
+};
+
+#endif /* CONFIG_SYSFS */
+/*
+ * When zcache is disabled ("frozen"), pools can be created and destroyed,
+ * but all puts (and thus all other operations that require memory allocation)
+ * must fail.  If zcache is unfrozen, accepts puts, then frozen again,
+ * data consistency requires all puts while frozen to be converted into
+ * flushes.
+ */
+static bool zcache_freeze;
+
+/*
+ * zcache shrinker interface (only useful for ephemeral pages, so zbud only)
+ */
+static int shrink_zcache_memory(struct shrinker *shrink, int nr, gfp_t gfp_mask)
+{
+	int ret = -1;
+
+	if (nr >= 0) {
+		if (!(gfp_mask & __GFP_FS))
+			/* does this case really need to be skipped? */
+			goto out;
+		if (spin_trylock(&zcache_direct_reclaim_lock)) {
+			zbud_evict_pages(nr);
+			spin_unlock(&zcache_direct_reclaim_lock);
+		} else
+			zcache_aborted_shrink++;
+	}
+	ret = (int)atomic_read(&zcache_zbud_curr_raw_pages);
+out:
+	return ret;
+}
+
+static struct shrinker zcache_shrinker = {
+	.shrink = shrink_zcache_memory,
+	.seeks = DEFAULT_SEEKS,
+};
+
+/*
+ * zcache shims between cleancache/frontswap ops and tmem
+ */
+
+static int zcache_put_page(int pool_id, struct tmem_oid *oidp,
+				uint32_t index, struct page *page)
+{
+	struct tmem_pool *pool;
+	int ret = -1;
+
+	BUG_ON(!irqs_disabled());
+	pool = zcache_get_pool_by_id(pool_id);
+	if (unlikely(pool == NULL))
+		goto out;
+	if (!zcache_freeze && zcache_do_preload(pool) == 0) {
+		/* preload does preempt_disable on success */
+		ret = tmem_put(pool, oidp, index, page);
+		if (ret < 0) {
+			if (is_ephemeral(pool))
+				zcache_failed_eph_puts++;
+			else
+				zcache_failed_pers_puts++;
+		}
+		zcache_put_pool(pool);
+		preempt_enable_no_resched();
+	} else {
+		zcache_put_to_flush++;
+		if (atomic_read(&pool->obj_count) > 0)
+			/* the put fails whether the flush succeeds or not */
+			(void)tmem_flush_page(pool, oidp, index);
+		zcache_put_pool(pool);
+	}
+out:
+	return ret;
+}
+
+static int zcache_get_page(int pool_id, struct tmem_oid *oidp,
+				uint32_t index, struct page *page)
+{
+	struct tmem_pool *pool;
+	int ret = -1;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	pool = zcache_get_pool_by_id(pool_id);
+	if (likely(pool != NULL)) {
+		if (atomic_read(&pool->obj_count) > 0)
+			ret = tmem_get(pool, oidp, index, page);
+		zcache_put_pool(pool);
+	}
+	local_irq_restore(flags);
+	return ret;
+}
+
+static int zcache_flush_page(int pool_id, struct tmem_oid *oidp, uint32_t index)
+{
+	struct tmem_pool *pool;
+	int ret = -1;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	zcache_flush_total++;
+	pool = zcache_get_pool_by_id(pool_id);
+	if (likely(pool != NULL)) {
+		if (atomic_read(&pool->obj_count) > 0)
+			ret = tmem_flush_page(pool, oidp, index);
+		zcache_put_pool(pool);
+	}
+	if (ret >= 0)
+		zcache_flush_found++;
+	local_irq_restore(flags);
+	return ret;
+}
+
+static int zcache_flush_object(int pool_id, struct tmem_oid *oidp)
+{
+	struct tmem_pool *pool;
+	int ret = -1;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	zcache_flobj_total++;
+	pool = zcache_get_pool_by_id(pool_id);
+	if (likely(pool != NULL)) {
+		if (atomic_read(&pool->obj_count) > 0)
+			ret = tmem_flush_object(pool, oidp);
+		zcache_put_pool(pool);
+	}
+	if (ret >= 0)
+		zcache_flobj_found++;
+	local_irq_restore(flags);
+	return ret;
+}
+
+static int zcache_destroy_pool(int pool_id)
+{
+	struct tmem_pool *pool = NULL;
+	int ret = -1;
+
+	if (pool_id < 0)
+		goto out;
+	pool = zcache_client.tmem_pools[pool_id];
+	if (pool == NULL)
+		goto out;
+	zcache_client.tmem_pools[pool_id] = NULL;
+	/* wait for pool activity on other cpus to quiesce */
+	while (atomic_read(&pool->refcount) != 0)
+		;
+	local_bh_disable();
+	ret = tmem_destroy_pool(pool);
+	local_bh_enable();
+	kfree(pool);
+	pr_info("zcache: destroyed pool id=%d\n", pool_id);
+out:
+	return ret;
+}
+
+static int zcache_new_pool(uint32_t flags)
+{
+	int poolid = -1;
+	struct tmem_pool *pool;
+
+	pool = kmalloc(sizeof(struct tmem_pool), GFP_KERNEL);
+	if (pool == NULL) {
+		pr_info("zcache: pool creation failed: out of memory\n");
+		goto out;
+	}
+
+	for (poolid = 0; poolid < MAX_POOLS_PER_CLIENT; poolid++)
+		if (zcache_client.tmem_pools[poolid] == NULL)
+			break;
+	if (poolid >= MAX_POOLS_PER_CLIENT) {
+		pr_info("zcache: pool creation failed: max exceeded\n");
+		kfree(pool);
+		poolid = -1;
+		goto out;
+	}
+	atomic_set(&pool->refcount, 0);
+	pool->client = &zcache_client;
+	pool->pool_id = poolid;
+	tmem_new_pool(pool, flags);
+	zcache_client.tmem_pools[poolid] = pool;
+	pr_info("zcache: created %s tmem pool, id=%d\n",
+		flags & TMEM_POOL_PERSIST ? "persistent" : "ephemeral",
+		poolid);
+out:
+	return poolid;
+}
+
+/**********
+ * Two kernel functionalities currently can be layered on top of tmem.
+ * These are "cleancache" which is used as a second-chance cache for clean
+ * page cache pages; and "frontswap" which is used for swap pages
+ * to avoid writes to disk.  A generic "shim" is provided here for each
+ * to translate in-kernel semantics to zcache semantics.
+ */
+
+#ifdef CONFIG_CLEANCACHE
+static void zcache_cleancache_put_page(int pool_id,
+					struct cleancache_filekey key,
+					pgoff_t index, struct page *page)
+{
+	u32 ind = (u32) index;
+	struct tmem_oid oid = *(struct tmem_oid *)&key;
+
+	if (likely(ind == index))
+		(void)zcache_put_page(pool_id, &oid, index, page);
+}
+
+static int zcache_cleancache_get_page(int pool_id,
+					struct cleancache_filekey key,
+					pgoff_t index, struct page *page)
+{
+	u32 ind = (u32) index;
+	struct tmem_oid oid = *(struct tmem_oid *)&key;
+	int ret = -1;
+
+	if (likely(ind == index))
+		ret = zcache_get_page(pool_id, &oid, index, page);
+	return ret;
+}
+
+static void zcache_cleancache_flush_page(int pool_id,
+					struct cleancache_filekey key,
+					pgoff_t index)
+{
+	u32 ind = (u32) index;
+	struct tmem_oid oid = *(struct tmem_oid *)&key;
+
+	if (likely(ind == index))
+		(void)zcache_flush_page(pool_id, &oid, ind);
+}
+
+static void zcache_cleancache_flush_inode(int pool_id,
+					struct cleancache_filekey key)
+{
+	struct tmem_oid oid = *(struct tmem_oid *)&key;
+
+	(void)zcache_flush_object(pool_id, &oid);
+}
+
+static void zcache_cleancache_flush_fs(int pool_id)
+{
+	if (pool_id >= 0)
+		(void)zcache_destroy_pool(pool_id);
+}
+
+static int zcache_cleancache_init_fs(size_t pagesize)
+{
+	BUG_ON(sizeof(struct cleancache_filekey) !=
+				sizeof(struct tmem_oid));
+	BUG_ON(pagesize != PAGE_SIZE);
+	return zcache_new_pool(0);
+}
+
+static int zcache_cleancache_init_shared_fs(char *uuid, size_t pagesize)
+{
+	/* shared pools are unsupported and map to private */
+	BUG_ON(sizeof(struct cleancache_filekey) !=
+				sizeof(struct tmem_oid));
+	BUG_ON(pagesize != PAGE_SIZE);
+	return zcache_new_pool(0);
+}
+
+static struct cleancache_ops zcache_cleancache_ops = {
+	.put_page = zcache_cleancache_put_page,
+	.get_page = zcache_cleancache_get_page,
+	.flush_page = zcache_cleancache_flush_page,
+	.flush_inode = zcache_cleancache_flush_inode,
+	.flush_fs = zcache_cleancache_flush_fs,
+	.init_shared_fs = zcache_cleancache_init_shared_fs,
+	.init_fs = zcache_cleancache_init_fs
+};
+
+struct cleancache_ops zcache_cleancache_register_ops(void)
+{
+	struct cleancache_ops old_ops =
+		cleancache_register_ops(&zcache_cleancache_ops);
+
+	return old_ops;
+}
+#endif
+
+#ifdef CONFIG_FRONTSWAP
+/* a single tmem poolid is used for all frontswap "types" (swapfiles) */
+static int zcache_frontswap_poolid = -1;
+
+/*
+ * Swizzling increases objects per swaptype, increasing tmem concurrency
+ * for heavy swaploads.  Later, larger nr_cpus -> larger SWIZ_BITS
+ */
+#define SWIZ_BITS		4
+#define SWIZ_MASK		((1 << SWIZ_BITS) - 1)
+#define _oswiz(_type, _ind)	((_type << SWIZ_BITS) | (_ind & SWIZ_MASK))
+#define iswiz(_ind)		(_ind >> SWIZ_BITS)
+
+static inline struct tmem_oid oswiz(unsigned type, u32 ind)
+{
+	struct tmem_oid oid = { .oid = { 0 } };
+	oid.oid[0] = _oswiz(type, ind);
+	return oid;
+}
+
+static int zcache_frontswap_put_page(unsigned type, pgoff_t offset,
+				   struct page *page)
+{
+	u64 ind64 = (u64)offset;
+	u32 ind = (u32)offset;
+	struct tmem_oid oid = oswiz(type, ind);
+	int ret = -1;
+	unsigned long flags;
+
+	BUG_ON(!PageLocked(page));
+	if (likely(ind64 == ind)) {
+		local_irq_save(flags);
+		ret = zcache_put_page(zcache_frontswap_poolid, &oid,
+					iswiz(ind), page);
+		local_irq_restore(flags);
+	}
+	return ret;
+}
+
+/* returns 0 if the page was successfully gotten from frontswap, -1 if
+ * was not present (should never happen!) */
+static int zcache_frontswap_get_page(unsigned type, pgoff_t offset,
+				   struct page *page)
+{
+	u64 ind64 = (u64)offset;
+	u32 ind = (u32)offset;
+	struct tmem_oid oid = oswiz(type, ind);
+	int ret = -1;
+
+	BUG_ON(!PageLocked(page));
+	if (likely(ind64 == ind))
+		ret = zcache_get_page(zcache_frontswap_poolid, &oid,
+					iswiz(ind), page);
+	return ret;
+}
+
+/* flush a single page from frontswap */
+static void zcache_frontswap_flush_page(unsigned type, pgoff_t offset)
+{
+	u64 ind64 = (u64)offset;
+	u32 ind = (u32)offset;
+	struct tmem_oid oid = oswiz(type, ind);
+
+	if (likely(ind64 == ind))
+		(void)zcache_flush_page(zcache_frontswap_poolid, &oid,
+					iswiz(ind));
+}
+
+/* flush all pages from the passed swaptype */
+static void zcache_frontswap_flush_area(unsigned type)
+{
+	struct tmem_oid oid;
+	int ind;
+
+	for (ind = SWIZ_MASK; ind >= 0; ind--) {
+		oid = oswiz(type, ind);
+		(void)zcache_flush_object(zcache_frontswap_poolid, &oid);
+	}
+}
+
+static void zcache_frontswap_init(unsigned ignored)
+{
+	/* a single tmem poolid is used for all frontswap "types" (swapfiles) */
+	if (zcache_frontswap_poolid < 0)
+		zcache_frontswap_poolid = zcache_new_pool(TMEM_POOL_PERSIST);
+}
+
+static struct frontswap_ops zcache_frontswap_ops = {
+	.put_page = zcache_frontswap_put_page,
+	.get_page = zcache_frontswap_get_page,
+	.flush_page = zcache_frontswap_flush_page,
+	.flush_area = zcache_frontswap_flush_area,
+	.init = zcache_frontswap_init
+};
+
+struct frontswap_ops zcache_frontswap_register_ops(void)
+{
+	struct frontswap_ops old_ops =
+		frontswap_register_ops(&zcache_frontswap_ops);
+
+	return old_ops;
+}
+#endif
+
+/*
+ * zcache initialization
+ * NOTE FOR NOW zcache MUST BE PROVIDED AS A KERNEL BOOT PARAMETER OR
+ * NOTHING HAPPENS!
+ */
+
+static int zcache_enabled;
+
+static int __init enable_zcache(char *s)
+{
+	zcache_enabled = 1;
+	return 1;
+}
+__setup("zcache", enable_zcache);
+
+/* allow independent dynamic disabling of cleancache and frontswap */
+
+static int use_cleancache = 1;
+
+static int __init no_cleancache(char *s)
+{
+	use_cleancache = 0;
+	return 1;
+}
+
+__setup("nocleancache", no_cleancache);
+
+static int use_frontswap = 1;
+
+static int __init no_frontswap(char *s)
+{
+	use_frontswap = 0;
+	return 1;
+}
+
+__setup("nofrontswap", no_frontswap);
+
+static int __init zcache_init(void)
+{
+#ifdef CONFIG_SYSFS
+	int ret = 0;
+
+	ret = sysfs_create_group(mm_kobj, &zcache_attr_group);
+	if (ret) {
+		pr_err("zcache: can't create sysfs\n");
+		goto out;
+	}
+#endif /* CONFIG_SYSFS */
+#if defined(CONFIG_CLEANCACHE) || defined(CONFIG_FRONTSWAP)
+	if (zcache_enabled) {
+		unsigned int cpu;
+
+		tmem_register_hostops(&zcache_hostops);
+		tmem_register_pamops(&zcache_pamops);
+		ret = register_cpu_notifier(&zcache_cpu_notifier_block);
+		if (ret) {
+			pr_err("zcache: can't register cpu notifier\n");
+			goto out;
+		}
+		for_each_online_cpu(cpu) {
+			void *pcpu = (void *)(long)cpu;
+			zcache_cpu_notifier(&zcache_cpu_notifier_block,
+				CPU_UP_PREPARE, pcpu);
+		}
+	}
+	zcache_objnode_cache = kmem_cache_create("zcache_objnode",
+				sizeof(struct tmem_objnode), 0, 0, NULL);
+	zcache_obj_cache = kmem_cache_create("zcache_obj",
+				sizeof(struct tmem_obj), 0, 0, NULL);
+#endif
+#ifdef CONFIG_CLEANCACHE
+	if (zcache_enabled && use_cleancache) {
+		struct cleancache_ops old_ops;
+
+		zbud_init();
+		register_shrinker(&zcache_shrinker);
+		old_ops = zcache_cleancache_register_ops();
+		pr_info("zcache: cleancache enabled using kernel "
+			"transcendent memory and compression buddies\n");
+		if (old_ops.init_fs != NULL)
+			pr_warning("zcache: cleancache_ops overridden");
+	}
+#endif
+#ifdef CONFIG_FRONTSWAP
+	if (zcache_enabled && use_frontswap) {
+		struct frontswap_ops old_ops;
+
+		zcache_client.xvpool = xv_create_pool();
+		if (zcache_client.xvpool == NULL) {
+			pr_err("zcache: can't create xvpool\n");
+			goto out;
+		}
+		old_ops = zcache_frontswap_register_ops();
+		pr_info("zcache: frontswap enabled using kernel "
+			"transcendent memory and xvmalloc\n");
+		if (old_ops.init != NULL)
+			pr_warning("ktmem: frontswap_ops overridden");
+	}
+#endif
+out:
+	return ret;
+}
+
+module_init(zcache_init)