zram: Restore deduplication feature

Change-Id: I09c77366b1ac0f6cc7c6f0f28197e48d2e1d3270
Signed-off-by: Richard Raya <rdxzv.dev@gmail.com>

Documentation/ABI/testing/sysfs-block-zram

@@ -99,6 +99,16 @@ Description:
 		device for zram to write incompressible pages.
 		For using, user should enable CONFIG_ZRAM_WRITEBACK.
 
+What:		/sys/block/zram<id>/use_dedup
+Date:		March 2017
+Contact:	Joonsoo Kim <iamjoonsoo.kim@lge.com>
+Description:
+		The use_dedup file is read-write and specifies deduplication
+		feature is used or not. If enabled, duplicated data is
+		managed by reference count and will not be stored in memory
+		twice. Benefit of this feature largely depends on the workload
+		so keep attention when use.
+
 What:		/sys/block/zram<id>/idle
 Date:		November 2018
 Contact:	Minchan Kim <minchan@kernel.org>

Documentation/blockdev/zram.txt

@@ -172,6 +172,7 @@ comp_algorithm    	RW	show and change the compression algorithm
 compact           	WO	trigger memory compaction
 debug_stat        	RO	this file is used for zram debugging purposes
 backing_dev	  	RW	set up backend storage for zram to write out
+use_dedup		RW	show and set deduplication feature
 idle		  	WO	mark allocated slot as idle
 
 User space is advised to use the following files to read the device statistics.
@@ -221,6 +222,8 @@ line of text and contains the following stats separated by whitespace:
  same_pages       the number of same element filled pages written to this disk.
                   No memory is allocated for such pages.
  pages_compacted  the number of pages freed during compaction
+ dup_data_size	  deduplicated data size
+ meta_data_size	  the amount of metadata allocated for deduplication feature
  huge_pages	  the number of incompressible pages
 
 File /sys/block/zram<id>/bd_stat

drivers/block/zram/Kconfig

@@ -40,6 +40,20 @@ config ZRAM_DEF_COMP
 	default "zstd" if ZRAM_DEF_COMP_ZSTD
 	default "lz4" if ZRAM_DEF_COMP_LZ4
 
+config ZRAM_DEDUP
+	bool "Deduplication support for ZRAM data"
+	depends on ZRAM && LIBCRC32C
+	default n
+	help
+	  Deduplicate ZRAM data to reduce amount of memory consumption.
+	  Advantage largely depends on the workload. In some cases, this
+          option reduces memory usage to the half. However, if there is no
+	  duplicated data, the amount of memory consumption would be
+	  increased due to additional metadata usage. And, there is
+	  computation time trade-off. Please check the benefit before
+	  enabling this option. Experiment shows the positive effect when
+	  the zram is used as blockdev and is used to store build output.
+
 config ZRAM_WRITEBACK
        bool "Write back incompressible or idle page to backing device"
        depends on ZRAM

drivers/block/zram/Makefile

@@ -1,2 +1,4 @@
 zram-y				:=	zcomp.o zram_drv.o
+zram-$(CONFIG_ZRAM_DEDUP)	+=	zram_dedup.o
+
 obj-$(CONFIG_ZRAM)	+=	zram.o

drivers/block/zram/zram_dedup.c

@@ -0,0 +1,255 @@
+/*
+ * Copyright (C) 2017 Joonsoo Kim.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/vmalloc.h>
+#include <linux/crc32c.h>
+#include <linux/highmem.h>
+
+#include "zram_drv.h"
+
+/* One slot will contain 128 pages theoretically */
+#define ZRAM_HASH_SHIFT		7
+#define ZRAM_HASH_SIZE_MIN	(1 << 10)
+#define ZRAM_HASH_SIZE_MAX	(1 << 31)
+
+u64 zram_dedup_dup_size(struct zram *zram)
+{
+	return (u64)atomic64_read(&zram->stats.dup_data_size);
+}
+
+u64 zram_dedup_meta_size(struct zram *zram)
+{
+	return (u64)atomic64_read(&zram->stats.meta_data_size);
+}
+
+static u32 zram_dedup_checksum(unsigned char *mem)
+{
+	return crc32c(0, mem, PAGE_SIZE);
+}
+
+void zram_dedup_insert(struct zram *zram, struct zram_entry *new,
+				u32 checksum)
+{
+	struct zram_hash *hash;
+	struct rb_root *rb_root;
+	struct rb_node **rb_node, *parent = NULL;
+	struct zram_entry *entry;
+
+	if (!zram_dedup_enabled(zram))
+		return;
+
+	new->checksum = checksum;
+	hash = &zram->hash[checksum % zram->hash_size];
+	rb_root = &hash->rb_root;
+
+	spin_lock(&hash->lock);
+	rb_node = &rb_root->rb_node;
+	while (*rb_node) {
+		parent = *rb_node;
+		entry = rb_entry(parent, struct zram_entry, rb_node);
+		if (checksum < entry->checksum)
+			rb_node = &parent->rb_left;
+		else if (checksum > entry->checksum)
+			rb_node = &parent->rb_right;
+		else
+			rb_node = &parent->rb_left;
+	}
+
+	rb_link_node(&new->rb_node, parent, rb_node);
+	rb_insert_color(&new->rb_node, rb_root);
+	spin_unlock(&hash->lock);
+}
+
+static bool zram_dedup_match(struct zram *zram, struct zram_entry *entry,
+				unsigned char *mem)
+{
+	bool match = false;
+	unsigned char *cmem;
+	struct zcomp_strm *zstrm;
+
+	cmem = zs_map_object(zram->mem_pool, entry->handle, ZS_MM_RO);
+	if (entry->len == PAGE_SIZE) {
+		match = !memcmp(mem, cmem, PAGE_SIZE);
+	} else {
+		zstrm = zcomp_stream_get(zram->comp);
+		if (!zcomp_decompress(zstrm, cmem, entry->len, zstrm->buffer))
+			match = !memcmp(mem, zstrm->buffer, PAGE_SIZE);
+		zcomp_stream_put(zram->comp);
+	}
+	zs_unmap_object(zram->mem_pool, entry->handle);
+
+	return match;
+}
+
+static unsigned long zram_dedup_put(struct zram *zram,
+				struct zram_entry *entry)
+{
+	struct zram_hash *hash;
+	u32 checksum;
+	unsigned long val;
+
+	checksum = entry->checksum;
+	hash = &zram->hash[checksum % zram->hash_size];
+
+	spin_lock(&hash->lock);
+
+	val = --entry->refcount;
+	if (!entry->refcount)
+		rb_erase(&entry->rb_node, &hash->rb_root);
+	else
+		atomic64_sub(entry->len, &zram->stats.dup_data_size);
+
+	spin_unlock(&hash->lock);
+
+	return val;
+}
+
+static struct zram_entry *__zram_dedup_get(struct zram *zram,
+				struct zram_hash *hash, unsigned char *mem,
+				struct zram_entry *entry)
+{
+	struct zram_entry *tmp, *prev = NULL;
+	struct rb_node *rb_node;
+
+	/* find left-most entry with same checksum */
+	while ((rb_node = rb_prev(&entry->rb_node))) {
+		tmp = rb_entry(rb_node, struct zram_entry, rb_node);
+		if (tmp->checksum != entry->checksum)
+			break;
+
+		entry = tmp;
+	}
+
+again:
+	entry->refcount++;
+	atomic64_add(entry->len, &zram->stats.dup_data_size);
+	spin_unlock(&hash->lock);
+
+	if (prev)
+		zram_entry_free(zram, prev);
+
+	if (zram_dedup_match(zram, entry, mem))
+		return entry;
+
+	spin_lock(&hash->lock);
+	tmp = NULL;
+	rb_node = rb_next(&entry->rb_node);
+	if (rb_node)
+		tmp = rb_entry(rb_node, struct zram_entry, rb_node);
+
+	if (tmp && (tmp->checksum == entry->checksum)) {
+		prev = entry;
+		entry = tmp;
+		goto again;
+	}
+
+	spin_unlock(&hash->lock);
+	zram_entry_free(zram, entry);
+
+	return NULL;
+}
+
+static struct zram_entry *zram_dedup_get(struct zram *zram,
+				unsigned char *mem, u32 checksum)
+{
+	struct zram_hash *hash;
+	struct zram_entry *entry;
+	struct rb_node *rb_node;
+
+	hash = &zram->hash[checksum % zram->hash_size];
+
+	spin_lock(&hash->lock);
+	rb_node = hash->rb_root.rb_node;
+	while (rb_node) {
+		entry = rb_entry(rb_node, struct zram_entry, rb_node);
+		if (checksum == entry->checksum)
+			return __zram_dedup_get(zram, hash, mem, entry);
+
+		if (checksum < entry->checksum)
+			rb_node = rb_node->rb_left;
+		else
+			rb_node = rb_node->rb_right;
+	}
+	spin_unlock(&hash->lock);
+
+	return NULL;
+}
+
+struct zram_entry *zram_dedup_find(struct zram *zram, struct page *page,
+				u32 *checksum)
+{
+	void *mem;
+	struct zram_entry *entry;
+
+	if (!zram_dedup_enabled(zram))
+		return NULL;
+
+	mem = kmap_atomic(page);
+	*checksum = zram_dedup_checksum(mem);
+
+	entry = zram_dedup_get(zram, mem, *checksum);
+	kunmap_atomic(mem);
+
+	return entry;
+}
+
+void zram_dedup_init_entry(struct zram *zram, struct zram_entry *entry,
+				unsigned long handle, unsigned int len)
+{
+	if (!zram_dedup_enabled(zram))
+		return;
+
+	entry->handle = handle;
+	entry->refcount = 1;
+	entry->len = len;
+}
+
+bool zram_dedup_put_entry(struct zram *zram, struct zram_entry *entry)
+{
+	if (!zram_dedup_enabled(zram))
+		return true;
+
+	if (zram_dedup_put(zram, entry))
+		return false;
+
+	return true;
+}
+
+int zram_dedup_init(struct zram *zram, size_t num_pages)
+{
+	int i;
+	struct zram_hash *hash;
+
+	if (!zram_dedup_enabled(zram))
+		return 0;
+
+	zram->hash_size = num_pages >> ZRAM_HASH_SHIFT;
+	zram->hash_size = min_t(size_t, ZRAM_HASH_SIZE_MAX, zram->hash_size);
+	zram->hash_size = max_t(size_t, ZRAM_HASH_SIZE_MIN, zram->hash_size);
+	zram->hash = vzalloc(zram->hash_size * sizeof(struct zram_hash));
+	if (!zram->hash) {
+		pr_err("Error allocating zram entry hash\n");
+		return -ENOMEM;
+	}
+
+	for (i = 0; i < zram->hash_size; i++) {
+		hash = &zram->hash[i];
+		spin_lock_init(&hash->lock);
+		hash->rb_root = RB_ROOT;
+	}
+
+	return 0;
+}
+
+void zram_dedup_deinit(struct zram *zram)
+{
+	vfree(zram->hash);
+	zram->hash = NULL;
+	zram->hash_size = 0;
+}

drivers/block/zram/zram_dedup.h

@@ -0,0 +1,45 @@
+#ifndef _ZRAM_DEDUP_H_
+#define _ZRAM_DEDUP_H_
+
+struct zram;
+struct zram_entry;
+
+#ifdef CONFIG_ZRAM_DEDUP
+
+u64 zram_dedup_dup_size(struct zram *zram);
+u64 zram_dedup_meta_size(struct zram *zram);
+
+void zram_dedup_insert(struct zram *zram, struct zram_entry *new,
+				u32 checksum);
+struct zram_entry *zram_dedup_find(struct zram *zram, struct page *page,
+				u32 *checksum);
+
+void zram_dedup_init_entry(struct zram *zram, struct zram_entry *entry,
+				unsigned long handle, unsigned int len);
+bool zram_dedup_put_entry(struct zram *zram, struct zram_entry *entry);
+
+int zram_dedup_init(struct zram *zram, size_t num_pages);
+void zram_dedup_deinit(struct zram *zram);
+#else
+
+static inline u64 zram_dedup_dup_size(struct zram *zram) { return 0; }
+static inline u64 zram_dedup_meta_size(struct zram *zram) { return 0; }
+
+static inline void zram_dedup_insert(struct zram *zram, struct zram_entry *new,
+			u32 checksum) { }
+static inline struct zram_entry *zram_dedup_find(struct zram *zram,
+			struct page *page, u32 *checksum) { return NULL; }
+
+static inline void zram_dedup_init_entry(struct zram *zram,
+			struct zram_entry *entry, unsigned long handle,
+			unsigned int len) { }
+static inline bool zram_dedup_put_entry(struct zram *zram,
+			struct zram_entry *entry) { return true; }
+
+static inline int zram_dedup_init(struct zram *zram,
+			size_t num_pages) { return 0; }
+static inline void zram_dedup_deinit(struct zram *zram) { }
+
+#endif
+
+#endif /* _ZRAM_DEDUP_H_ */

drivers/block/zram/zram_drv.c

@@ -84,14 +84,15 @@ static inline struct zram *dev_to_zram(struct device *dev)
 	return (struct zram *)dev_to_disk(dev)->private_data;
 }
 
-static unsigned long zram_get_handle(struct zram *zram, u32 index)
+static struct zram_entry *zram_get_entry(struct zram *zram, u32 index)
 {
-	return zram->table[index].handle;
+	return zram->table[index].entry;
 }
 
-static void zram_set_handle(struct zram *zram, u32 index, unsigned long handle)
+static void zram_set_entry(struct zram *zram, u32 index,
+			struct zram_entry *entry)
 {
-	zram->table[index].handle = handle;
+	zram->table[index].entry = entry;
 }
 
 /* flag operations require table entry bit_spin_lock() being held */
@@ -1040,6 +1041,41 @@ static ssize_t comp_algorithm_store(struct device *dev,
 	return len;
 }
 
+static ssize_t use_dedup_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	bool val;
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	val = zram->use_dedup;
+	up_read(&zram->init_lock);
+
+	return scnprintf(buf, PAGE_SIZE, "%d\n", (int)val);
+}
+
+#ifdef CONFIG_ZRAM_DEDUP
+static ssize_t use_dedup_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	int val;
+	struct zram *zram = dev_to_zram(dev);
+
+	if (kstrtoint(buf, 10, &val) || (val != 0 && val != 1))
+		return -EINVAL;
+
+	down_write(&zram->init_lock);
+	if (init_done(zram)) {
+		up_write(&zram->init_lock);
+		pr_info("Can't change dedup usage for initialized device\n");
+		return -EBUSY;
+	}
+	zram->use_dedup = val;
+	up_write(&zram->init_lock);
+	return len;
+}
+#endif
+
 static ssize_t compact_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
@@ -1096,7 +1132,7 @@ static ssize_t mm_stat_show(struct device *dev,
 	max_used = atomic_long_read(&zram->stats.max_used_pages);
 
 	ret = scnprintf(buf, PAGE_SIZE,
-			"%8llu %8llu %8llu %8lu %8ld %8llu %8lu %8llu\n",
+			"%8llu %8llu %8llu %8lu %8ld %8llu %8lu %8llu %8llu %8llu\n",
 			orig_size << PAGE_SHIFT,
 			(u64)atomic64_read(&zram->stats.compr_data_size),
 			mem_used << PAGE_SHIFT,
@@ -1104,6 +1140,8 @@ static ssize_t mm_stat_show(struct device *dev,
 			max_used << PAGE_SHIFT,
 			(u64)atomic64_read(&zram->stats.same_pages),
 			atomic_long_read(&pool_stats.pages_compacted),
+			zram_dedup_dup_size(zram),
+			zram_dedup_meta_size(zram),
 			(u64)atomic64_read(&zram->stats.huge_pages),
 			(u64)atomic64_read(&zram->stats.huge_pages_since));
 	up_read(&zram->init_lock);
@@ -1156,6 +1194,56 @@ static DEVICE_ATTR_RO(bd_stat);
 #endif
 static DEVICE_ATTR_RO(debug_stat);
 
+static unsigned long zram_entry_handle(struct zram *zram,
+		struct zram_entry *entry)
+{
+	if (zram_dedup_enabled(zram))
+		return entry->handle;
+	else
+		return (unsigned long)entry;
+}
+
+static struct zram_entry *zram_entry_alloc(struct zram *zram,
+					   unsigned int len, gfp_t flags)
+{
+	struct zram_entry *entry;
+	unsigned long handle;
+
+	handle = zs_malloc(zram->mem_pool, len, flags);
+	if (!handle)
+		return NULL;
+
+	if (!zram_dedup_enabled(zram))
+		return (struct zram_entry *)handle;
+
+	entry = kzalloc(sizeof(*entry),
+			flags & ~(__GFP_HIGHMEM|__GFP_MOVABLE|__GFP_CMA));
+	if (!entry) {
+		zs_free(zram->mem_pool, handle);
+		return NULL;
+	}
+
+	zram_dedup_init_entry(zram, entry, handle, len);
+	atomic64_add(sizeof(*entry), &zram->stats.meta_data_size);
+
+	return entry;
+}
+
+void zram_entry_free(struct zram *zram, struct zram_entry *entry)
+{
+	if (!zram_dedup_put_entry(zram, entry))
+		return;
+
+	zs_free(zram->mem_pool, zram_entry_handle(zram, entry));
+
+	if (!zram_dedup_enabled(zram))
+		return;
+
+	kfree(entry);
+
+	atomic64_sub(sizeof(*entry), &zram->stats.meta_data_size);
+}
+
 static void zram_meta_free(struct zram *zram, u64 disksize)
 {
 	size_t num_pages = disksize >> PAGE_SHIFT;
@@ -1166,6 +1254,7 @@ static void zram_meta_free(struct zram *zram, u64 disksize)
 		zram_free_page(zram, index);
 
 	zs_destroy_pool(zram->mem_pool);
+	zram_dedup_deinit(zram);
 	vfree(zram->table);
 }
 
@@ -1187,6 +1276,12 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
 	if (!huge_class_size)
 		huge_class_size = zs_huge_class_size(zram->mem_pool);
 
+	if (zram_dedup_init(zram, num_pages)) {
+		vfree(zram->table);
+		zs_destroy_pool(zram->mem_pool);
+		return false;
+	}
+
 	return true;
 }
 
@@ -1197,7 +1292,7 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
  */
 static void zram_free_page(struct zram *zram, size_t index)
 {
-	unsigned long handle;
+	struct zram_entry *entry;
 
 #ifdef CONFIG_ZRAM_MEMORY_TRACKING
 	zram->table[index].ac_time = 0;
@@ -1226,17 +1321,17 @@ static void zram_free_page(struct zram *zram, size_t index)
 		goto out;
 	}
 
-	handle = zram_get_handle(zram, index);
-	if (!handle)
+	entry = zram_get_entry(zram, index);
+	if (!entry)
 		return;
 
-	zs_free(zram->mem_pool, handle);
+	zram_entry_free(zram, entry);
 
 	atomic64_sub(zram_get_obj_size(zram, index),
 			&zram->stats.compr_data_size);
 out:
 	atomic64_dec(&zram->stats.pages_stored);
-	zram_set_handle(zram, index, 0);
+	zram_set_entry(zram, index, NULL);
 	zram_set_obj_size(zram, index, 0);
 	WARN_ON_ONCE(zram->table[index].flags &
 		~(1UL << ZRAM_LOCK | 1UL << ZRAM_UNDER_WB));
@@ -1245,8 +1340,8 @@ out:
 static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 				struct bio *bio, bool partial_io)
 {
-	struct zcomp_strm *zstrm;
-	unsigned long handle;
+        struct zcomp_strm *zstrm;
+	struct zram_entry *entry;
 	unsigned int size;
 	void *src, *dst;
 	int ret;
@@ -1265,12 +1360,12 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 				bio, partial_io);
 	}
 
-	handle = zram_get_handle(zram, index);
-	if (!handle || zram_test_flag(zram, index, ZRAM_SAME)) {
+	entry = zram_get_entry(zram, index);
+	if (!entry || zram_test_flag(zram, index, ZRAM_SAME)) {
 		unsigned long value;
 		void *mem;
 
-		value = handle ? zram_get_element(zram, index) : 0;
+		value = entry ? zram_get_element(zram, index) : 0;
 		mem = kmap_atomic(page);
 		zram_fill_page(mem, PAGE_SIZE, value);
 		kunmap_atomic(mem);
@@ -1283,7 +1378,8 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 	if (size != PAGE_SIZE)
 		zstrm = zcomp_stream_get(zram->comp);
 
-	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
+	src = zs_map_object(zram->mem_pool,
+			    zram_entry_handle(zram, entry), ZS_MM_RO);
 	if (size == PAGE_SIZE) {
 		dst = kmap_atomic(page);
 		copy_page(dst, src);
@@ -1295,7 +1391,7 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 		kunmap_atomic(dst);
 		zcomp_stream_put(zram->comp);
 	}
-	zs_unmap_object(zram->mem_pool, handle);
+	zs_unmap_object(zram->mem_pool, zram_entry_handle(zram, entry));
 	zram_slot_unlock(zram, index);
 
 	/* Should NEVER happen. Return bio error if it does. */
@@ -1343,11 +1439,12 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 {
 	int ret = 0;
 	unsigned long alloced_pages;
-	unsigned long handle = 0;
+	struct zram_entry *entry = NULL;
 	unsigned int comp_len = 0;
 	void *src, *dst, *mem;
 	struct zcomp_strm *zstrm;
 	struct page *page = bvec->bv_page;
+	u32 checksum;
 	unsigned long element = 0;
 	enum zram_pageflags flags = 0;
 
@@ -1361,6 +1458,12 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 	}
 	kunmap_atomic(mem);
 
+	entry = zram_dedup_find(zram, page, &checksum);
+	if (entry) {
+		comp_len = entry->len;
+		goto out;
+	}
+
 compress_again:
 	zstrm = zcomp_stream_get(zram->comp);
 	src = kmap_atomic(page);
@@ -1370,39 +1473,40 @@ compress_again:
 	if (unlikely(ret)) {
 		zcomp_stream_put(zram->comp);
 		pr_err("Compression failed! err=%d\n", ret);
-		zs_free(zram->mem_pool, handle);
+		if (entry)
+			zram_entry_free(zram, entry);
 		return ret;
 	}
 
 	if (comp_len >= huge_class_size)
 		comp_len = PAGE_SIZE;
 	/*
-	 * handle allocation has 2 paths:
+	 * entry allocation has 2 paths:
 	 * a) fast path is executed with preemption disabled (for
 	 *  per-cpu streams) and has __GFP_DIRECT_RECLAIM bit clear,
 	 *  since we can't sleep;
 	 * b) slow path enables preemption and attempts to allocate
 	 *  the page with __GFP_DIRECT_RECLAIM bit set. we have to
 	 *  put per-cpu compression stream and, thus, to re-do
-	 *  the compression once handle is allocated.
+	 *  the compression once entry is allocated.
 	 *
-	 * if we have a 'non-null' handle here then we are coming
-	 * from the slow path and handle has already been allocated.
+	 * if we have a 'non-null' entry here then we are coming
+	 * from the slow path and entry has already been allocated.
 	 */
-	if (!handle)
-		handle = zs_malloc(zram->mem_pool, comp_len,
+	if (!entry)
+		entry = zram_entry_alloc(zram, comp_len,
 				__GFP_KSWAPD_RECLAIM |
 				__GFP_NOWARN |
 				__GFP_HIGHMEM |
 				__GFP_MOVABLE |
 				__GFP_CMA);
-	if (!handle) {
+	if (!entry) {
 		zcomp_stream_put(zram->comp);
 		atomic64_inc(&zram->stats.writestall);
-		handle = zs_malloc(zram->mem_pool, comp_len,
+		entry = zram_entry_alloc(zram, comp_len,
 				GFP_NOIO | __GFP_HIGHMEM |
 				__GFP_MOVABLE | __GFP_CMA);
-		if (handle)
+		if (entry)
 			goto compress_again;
 		return -ENOMEM;
 	}
@@ -1412,11 +1516,12 @@ compress_again:
 
 	if (zram->limit_pages && alloced_pages > zram->limit_pages) {
 		zcomp_stream_put(zram->comp);
-		zs_free(zram->mem_pool, handle);
+		zram_entry_free(zram, entry);
 		return -ENOMEM;
 	}
 
-	dst = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
+	dst = zs_map_object(zram->mem_pool,
+			    zram_entry_handle(zram, entry), ZS_MM_WO);
 
 	src = zstrm->buffer;
 	if (comp_len == PAGE_SIZE)
@@ -1426,8 +1531,9 @@ compress_again:
 		kunmap_atomic(src);
 
 	zcomp_stream_put(zram->comp);
-	zs_unmap_object(zram->mem_pool, handle);
+	zs_unmap_object(zram->mem_pool, zram_entry_handle(zram, entry));
 	atomic64_add(comp_len, &zram->stats.compr_data_size);
+	zram_dedup_insert(zram, entry, checksum);
 out:
 	/*
 	 * Free memory associated with this sector
@@ -1446,7 +1552,7 @@ out:
 		zram_set_flag(zram, index, flags);
 		zram_set_element(zram, index, element);
 	}  else {
-		zram_set_handle(zram, index, handle);
+		zram_set_entry(zram, index, entry);
 		zram_set_obj_size(zram, index, comp_len);
 	}
 	zram_slot_unlock(zram, index);
@@ -1867,6 +1973,11 @@ static DEVICE_ATTR_WO(writeback);
 static DEVICE_ATTR_RW(writeback_limit);
 static DEVICE_ATTR_RW(writeback_limit_enable);
 #endif
+#ifdef CONFIG_ZRAM_DEDUP
+static DEVICE_ATTR_RW(use_dedup);
+#else
+static DEVICE_ATTR_RO(use_dedup);
+#endif
 
 static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_disksize.attr,
@@ -1884,6 +1995,7 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_writeback_limit.attr,
 	&dev_attr_writeback_limit_enable.attr,
 #endif
+	&dev_attr_use_dedup.attr,
 	&dev_attr_io_stat.attr,
 	&dev_attr_mm_stat.attr,
 #ifdef CONFIG_ZRAM_WRITEBACK

drivers/block/zram/zram_drv.h

@@ -18,8 +18,10 @@
 #include <linux/rwsem.h>
 #include <linux/zsmalloc.h>
 #include <linux/crypto.h>
+#include <linux/spinlock.h>
 
 #include "zcomp.h"
+#include "zram_dedup.h"
 
 #define SECTORS_PER_PAGE_SHIFT	(PAGE_SHIFT - SECTOR_SHIFT)
 #define SECTORS_PER_PAGE	(1 << SECTORS_PER_PAGE_SHIFT)
@@ -56,10 +58,18 @@ enum zram_pageflags {
 
 /*-- Data structures */
 
+struct zram_entry {
+	struct rb_node rb_node;
+	u32 len;
+	u32 checksum;
+	unsigned long refcount;
+	unsigned long handle;
+};
+
 /* Allocated for each disk page */
 struct zram_table_entry {
 	union {
-		unsigned long handle;
+		struct zram_entry *entry;
 		unsigned long element;
 	};
 	unsigned long flags;
@@ -82,6 +92,11 @@ struct zram_stats {
 	atomic64_t pages_stored;	/* no. of pages currently stored */
 	atomic_long_t max_used_pages;	/* no. of maximum pages stored */
 	atomic64_t writestall;		/* no. of write slow paths */
+	atomic64_t dup_data_size;	/*
+					 * compressed size of pages
+					 * duplicated
+					 */
+	atomic64_t meta_data_size;	/* size of zram_entries */
 	atomic64_t miss_free;		/* no. of missed free */
 #ifdef	CONFIG_ZRAM_WRITEBACK
 	atomic64_t bd_count;		/* no. of pages in backing device */
@@ -90,11 +105,18 @@ struct zram_stats {
 #endif
 };
 
+struct zram_hash {
+	spinlock_t lock;
+	struct rb_root rb_root;
+};
+
 struct zram {
 	struct zram_table_entry *table;
 	struct zs_pool *mem_pool;
 	struct zcomp *comp;
 	struct gendisk *disk;
+	struct zram_hash *hash;
+	size_t hash_size;
 	/* Prevent concurrent execution of device init */
 	struct rw_semaphore init_lock;
 	/*
@@ -113,8 +135,9 @@ struct zram {
 	 * zram is claimed so open request will be failed
 	 */
 	bool claim; /* Protected by bdev->bd_mutex */
+	bool use_dedup;
 #ifdef CONFIG_ZRAM_WRITEBACK
-	struct file *backing_dev;
+        struct file *backing_dev;
 	spinlock_t wb_limit_lock;
 	bool wb_limit_enable;
 	u64 bd_wb_limit;
@@ -126,4 +149,15 @@ struct zram {
 	struct dentry *debugfs_dir;
 #endif
 };
+
+static inline bool zram_dedup_enabled(struct zram *zram)
+{
+#ifdef CONFIG_ZRAM_DEDUP
+	return zram->use_dedup;
+#else
+	return false;
+#endif
+}
+
+void zram_entry_free(struct zram *zram, struct zram_entry *entry);
 #endif