6.1/0015-zram.patch

From 25ea938c3487e62133a4e6ed7f2367829e4f0a32 Mon Sep 17 00:00:00 2001
From: Peter Jung <admin@ptr1337.dev>
Date: Wed, 18 Jan 2023 13:24:16 +0100
Subject: [PATCH 15/16] zram

Signed-off-by: Peter Jung <admin@ptr1337.dev>
---
 Documentation/admin-guide/blockdev/zram.rst | 102 ++-
 drivers/block/zram/Kconfig                  |   9 +
 drivers/block/zram/zcomp.c                  |   6 +-
 drivers/block/zram/zcomp.h                  |   2 +-
 drivers/block/zram/zram_drv.c               | 918 ++++++++++++++++++--
 drivers/block/zram/zram_drv.h               |  29 +-
 include/linux/zsmalloc.h                    |   2 +
 mm/zsmalloc.c                               |  21 +
 8 files changed, 1005 insertions(+), 84 deletions(-)

diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
index c73b16930449..a1dd202efca1 100644
--- a/Documentation/admin-guide/blockdev/zram.rst
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -209,6 +209,7 @@ 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
 idle		  	WO	mark allocated slot as idle
+merge           	WO	trigger merge identical pages
 ======================  ======  ===============================================
 
 
@@ -267,6 +268,7 @@ line of text and contains the following stats separated by whitespace:
  pages_compacted  the number of pages freed during compaction
  huge_pages	  the number of incompressible pages
  huge_pages_since the number of incompressible pages since zram set up
+ pages_merged	  the number of identical pages merged into single one
  ================ =============================================================
 
 File /sys/block/zram<id>/bd_stat
@@ -348,8 +350,13 @@ this can be accomplished with::
 
         echo huge_idle > /sys/block/zramX/writeback
 
+If a user chooses to writeback only incompressible pages (pages that none of
+algorithms can compress) this can be accomplished with::
+
+	echo incompressible > /sys/block/zramX/writeback
+
 If an admin wants to write a specific page in zram device to the backing device,
-they could write a page index into the interface.
+they could write a page index into the interface::
 
 	echo "page_index=1251" > /sys/block/zramX/writeback
 
@@ -401,6 +408,87 @@ budget in next setting is user's job.
 If admin wants to measure writeback count in a certain period, they could
 know it via /sys/block/zram0/bd_stat's 3rd column.
 
+recompression
+-------------
+
+With CONFIG_ZRAM_MULTI_COMP, zram can recompress pages using alternative
+(secondary) compression algorithms. The basic idea is that alternative
+compression algorithm can provide better compression ratio at a price of
+(potentially) slower compression/decompression speeds. Alternative compression
+algorithm can, for example, be more successful compressing huge pages (those
+that default algorithm failed to compress). Another application is idle pages
+recompression - pages that are cold and sit in the memory can be recompressed
+using more effective algorithm and, hence, reduce zsmalloc memory usage.
+
+With CONFIG_ZRAM_MULTI_COMP, zram supports up to 4 compression algorithms:
+one primary and up to 3 secondary ones. Primary zram compressor is explained
+in "3) Select compression algorithm", secondary algorithms are configured
+using recomp_algorithm device attribute.
+
+Example:::
+
+	#show supported recompression algorithms
+	cat /sys/block/zramX/recomp_algorithm
+	#1: lzo lzo-rle lz4 lz4hc [zstd]
+	#2: lzo lzo-rle lz4 [lz4hc] zstd
+
+Alternative compression algorithms are sorted by priority. In the example
+above, zstd is used as the first alternative algorithm, which has priority
+of 1, while lz4hc is configured as a compression algorithm with priority 2.
+Alternative compression algorithm's priority is provided during algorithms
+configuration:::
+
+	#select zstd recompression algorithm, priority 1
+	echo "algo=zstd priority=1" > /sys/block/zramX/recomp_algorithm
+
+	#select deflate recompression algorithm, priority 2
+	echo "algo=deflate priority=2" > /sys/block/zramX/recomp_algorithm
+
+Another device attribute that CONFIG_ZRAM_MULTI_COMP enables is recompress,
+which controls recompression.
+
+Examples:::
+
+	#IDLE pages recompression is activated by `idle` mode
+	echo "type=idle" > /sys/block/zramX/recompress
+
+	#HUGE pages recompression is activated by `huge` mode
+	echo "type=huge" > /sys/block/zram0/recompress
+
+	#HUGE_IDLE pages recompression is activated by `huge_idle` mode
+	echo "type=huge_idle" > /sys/block/zramX/recompress
+
+The number of idle pages can be significant, so user-space can pass a size
+threshold (in bytes) to the recompress knob: zram will recompress only pages
+of equal or greater size:::
+
+	#recompress all pages larger than 3000 bytes
+	echo "threshold=3000" > /sys/block/zramX/recompress
+
+	#recompress idle pages larger than 2000 bytes
+	echo "type=idle threshold=2000" > /sys/block/zramX/recompress
+
+Recompression of idle pages requires memory tracking.
+
+During re-compression for every page, that matches re-compression criteria,
+ZRAM iterates the list of registered alternative compression algorithms in
+order of their priorities. ZRAM stops either when re-compression was
+successful (re-compressed object is smaller in size than the original one)
+and matches re-compression criteria (e.g. size threshold) or when there are
+no secondary algorithms left to try. If none of the secondary algorithms can
+successfully re-compressed the page such a page is marked as incompressible,
+so ZRAM will not attempt to re-compress it in the future.
+
+This re-compression behaviour, when it iterates through the list of
+registered compression algorithms, increases our chances of finding the
+algorithm that successfully compresses a particular page. Sometimes, however,
+it is convenient (and sometimes even necessary) to limit recompression to
+only one particular algorithm so that it will not try any other algorithms.
+This can be achieved by providing a algo=NAME parameter:::
+
+	#use zstd algorithm only (if registered)
+	echo "type=huge algo=zstd" > /sys/block/zramX/recompress
+
 memory tracking
 ===============
 
@@ -411,9 +499,11 @@ pages of the process with*pagemap.
 If you enable the feature, you could see block state via
 /sys/kernel/debug/zram/zram0/block_state". The output is as follows::
 
-	  300    75.033841 .wh.
-	  301    63.806904 s...
-	  302    63.806919 ..hi
+	  300    75.033841 .wh...
+	  301    63.806904 s.....
+	  302    63.806919 ..hi..
+	  303    62.801919 ....r.
+	  304   146.781902 ..hi.n
 
 First column
 	zram's block index.
@@ -430,6 +520,10 @@ Third column
 		huge page
 	i:
 		idle page
+	r:
+		recompressed page (secondary compression algorithm)
+	n:
+		none (including secondary) of algorithms could compress it
 
 First line of above example says 300th block is accessed at 75.033841sec
 and the block's state is huge so it is written back to the backing
diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index d4100b0c083e..0386b7da02aa 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -78,3 +78,12 @@ config ZRAM_MEMORY_TRACKING
 	  /sys/kernel/debug/zram/zramX/block_state.
 
 	  See Documentation/admin-guide/blockdev/zram.rst for more information.
+
+config ZRAM_MULTI_COMP
+	bool "Enable multiple compression streams"
+	depends on ZRAM
+	help
+	  This will enable multi-compression streams, so that ZRAM can
+	  re-compress pages using a potentially slower but more effective
+	  compression algorithm. Note, that IDLE page recompression
+	  requires ZRAM_MEMORY_TRACKING.
diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index 0916de952e09..55af4efd7983 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -206,7 +206,7 @@ void zcomp_destroy(struct zcomp *comp)
  * case of allocation error, or any other error potentially
  * returned by zcomp_init().
  */
-struct zcomp *zcomp_create(const char *compress)
+struct zcomp *zcomp_create(const char *alg)
 {
 	struct zcomp *comp;
 	int error;
@@ -216,14 +216,14 @@ struct zcomp *zcomp_create(const char *compress)
 	 * is not loaded yet. We must do it here, otherwise we are about to
 	 * call /sbin/modprobe under CPU hot-plug lock.
 	 */
-	if (!zcomp_available_algorithm(compress))
+	if (!zcomp_available_algorithm(alg))
 		return ERR_PTR(-EINVAL);
 
 	comp = kzalloc(sizeof(struct zcomp), GFP_KERNEL);
 	if (!comp)
 		return ERR_PTR(-ENOMEM);
 
-	comp->name = compress;
+	comp->name = alg;
 	error = zcomp_init(comp);
 	if (error) {
 		kfree(comp);
diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
index 40f6420f4b2e..cdefdef93da8 100644
--- a/drivers/block/zram/zcomp.h
+++ b/drivers/block/zram/zcomp.h
@@ -27,7 +27,7 @@ int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node);
 ssize_t zcomp_available_show(const char *comp, char *buf);
 bool zcomp_available_algorithm(const char *comp);
 
-struct zcomp *zcomp_create(const char *comp);
+struct zcomp *zcomp_create(const char *alg);
 void zcomp_destroy(struct zcomp *comp);
 
 struct zcomp_strm *zcomp_stream_get(struct zcomp *comp);
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 966aab902d19..88ca389aa478 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -33,12 +33,15 @@
 #include <linux/debugfs.h>
 #include <linux/cpuhotplug.h>
 #include <linux/part_stat.h>
+#include <linux/hashtable.h>
+#include <linux/xxhash.h>
 
 #include "zram_drv.h"
 
 static DEFINE_IDR(zram_index_idr);
 /* idr index must be protected */
 static DEFINE_MUTEX(zram_index_mutex);
+static DEFINE_MUTEX(zram_rbtree_mutex);
 
 static int zram_major;
 static const char *default_compressor = CONFIG_ZRAM_DEF_COMP;
@@ -57,6 +60,16 @@ static void zram_free_page(struct zram *zram, size_t index);
 static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 				u32 index, int offset, struct bio *bio);
 
+struct zram_rbtree_node {
+	struct rb_node node;
+	unsigned long key;
+	unsigned long cnt;
+};
+
+struct zram_hash_node {
+	unsigned long index;
+	struct hlist_node next;
+};
 
 static int zram_slot_trylock(struct zram *zram, u32 index)
 {
@@ -155,6 +168,25 @@ static inline bool is_partial_io(struct bio_vec *bvec)
 }
 #endif
 
+static inline void zram_set_priority(struct zram *zram, u32 index, u32 prio)
+{
+	prio &= ZRAM_COMP_PRIORITY_MASK;
+	/*
+	 * Clear previous priority value first, in case if we recompress
+	 * further an already recompressed page
+	 */
+	zram->table[index].flags &= ~(ZRAM_COMP_PRIORITY_MASK <<
+				      ZRAM_COMP_PRIORITY_BIT1);
+	zram->table[index].flags |= (prio << ZRAM_COMP_PRIORITY_BIT1);
+}
+
+static inline u32 zram_get_priority(struct zram *zram, u32 index)
+{
+	u32 prio = zram->table[index].flags >> ZRAM_COMP_PRIORITY_BIT1;
+
+	return prio & ZRAM_COMP_PRIORITY_MASK;
+}
+
 /*
  * Check if request is within bounds and aligned on zram logical blocks.
  */
@@ -629,10 +661,10 @@ static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
 
 #define PAGE_WB_SIG "page_index="
 
-#define PAGE_WRITEBACK 0
-#define HUGE_WRITEBACK (1<<0)
-#define IDLE_WRITEBACK (1<<1)
-
+#define PAGE_WRITEBACK			0
+#define HUGE_WRITEBACK			(1<<0)
+#define IDLE_WRITEBACK			(1<<1)
+#define INCOMPRESSIBLE_WRITEBACK	(1<<2)
 
 static ssize_t writeback_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
@@ -653,6 +685,8 @@ static ssize_t writeback_store(struct device *dev,
 		mode = HUGE_WRITEBACK;
 	else if (sysfs_streq(buf, "huge_idle"))
 		mode = IDLE_WRITEBACK | HUGE_WRITEBACK;
+	else if (sysfs_streq(buf, "incompressible"))
+		mode = INCOMPRESSIBLE_WRITEBACK;
 	else {
 		if (strncmp(buf, PAGE_WB_SIG, sizeof(PAGE_WB_SIG) - 1))
 			return -EINVAL;
@@ -715,11 +749,15 @@ static ssize_t writeback_store(struct device *dev,
 			goto next;
 
 		if (mode & IDLE_WRITEBACK &&
-			  !zram_test_flag(zram, index, ZRAM_IDLE))
+		    !zram_test_flag(zram, index, ZRAM_IDLE))
 			goto next;
 		if (mode & HUGE_WRITEBACK &&
-			  !zram_test_flag(zram, index, ZRAM_HUGE))
+		    !zram_test_flag(zram, index, ZRAM_HUGE))
 			goto next;
+		if (mode & INCOMPRESSIBLE_WRITEBACK &&
+		    !zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
+			goto next;
+
 		/*
 		 * Clearing ZRAM_UNDER_WB is duty of caller.
 		 * IOW, zram_free_page never clear it.
@@ -753,8 +791,12 @@ static ssize_t writeback_store(struct device *dev,
 			zram_clear_flag(zram, index, ZRAM_IDLE);
 			zram_slot_unlock(zram, index);
 			/*
-			 * Return last IO error unless every IO were
-			 * not suceeded.
+			 * BIO errors are not fatal, we continue and simply
+			 * attempt to writeback the remaining objects (pages).
+			 * At the same time we need to signal user-space that
+			 * some writes (at least one, but also could be all of
+			 * them) were not successful and we do so by returning
+			 * the most recent BIO error.
 			 */
 			ret = err;
 			continue;
@@ -920,13 +962,16 @@ static ssize_t read_block_state(struct file *file, char __user *buf,
 
 		ts = ktime_to_timespec64(zram->table[index].ac_time);
 		copied = snprintf(kbuf + written, count,
-			"%12zd %12lld.%06lu %c%c%c%c\n",
+			"%12zd %12lld.%06lu %c%c%c%c%c%c\n",
 			index, (s64)ts.tv_sec,
 			ts.tv_nsec / NSEC_PER_USEC,
 			zram_test_flag(zram, index, ZRAM_SAME) ? 's' : '.',
 			zram_test_flag(zram, index, ZRAM_WB) ? 'w' : '.',
 			zram_test_flag(zram, index, ZRAM_HUGE) ? 'h' : '.',
-			zram_test_flag(zram, index, ZRAM_IDLE) ? 'i' : '.');
+			zram_test_flag(zram, index, ZRAM_IDLE) ? 'i' : '.',
+			zram_get_priority(zram, index) ? 'r' : '.',
+			zram_test_flag(zram, index,
+				       ZRAM_INCOMPRESSIBLE) ? 'n' : '.');
 
 		if (count <= copied) {
 			zram_slot_unlock(zram, index);
@@ -1000,47 +1045,144 @@ static ssize_t max_comp_streams_store(struct device *dev,
 	return len;
 }
 
-static ssize_t comp_algorithm_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
+static void comp_algorithm_set(struct zram *zram, u32 prio, const char *alg)
 {
-	size_t sz;
-	struct zram *zram = dev_to_zram(dev);
+	/* Do not free statically defined compression algorithms */
+	if (zram->comp_algs[prio] != default_compressor)
+		kfree(zram->comp_algs[prio]);
+
+	zram->comp_algs[prio] = alg;
+}
+
+static ssize_t __comp_algorithm_show(struct zram *zram, u32 prio, char *buf)
+{
+	ssize_t sz;
 
 	down_read(&zram->init_lock);
-	sz = zcomp_available_show(zram->compressor, buf);
+	sz = zcomp_available_show(zram->comp_algs[prio], buf);
 	up_read(&zram->init_lock);
 
 	return sz;
 }
 
-static ssize_t comp_algorithm_store(struct device *dev,
-		struct device_attribute *attr, const char *buf, size_t len)
+static int __comp_algorithm_store(struct zram *zram, u32 prio, const char *buf)
 {
-	struct zram *zram = dev_to_zram(dev);
-	char compressor[ARRAY_SIZE(zram->compressor)];
+	char *compressor;
 	size_t sz;
 
-	strscpy(compressor, buf, sizeof(compressor));
+	sz = strlen(buf);
+	if (sz >= CRYPTO_MAX_ALG_NAME)
+		return -E2BIG;
+
+	compressor = kstrdup(buf, GFP_KERNEL);
+	if (!compressor)
+		return -ENOMEM;
+
 	/* ignore trailing newline */
-	sz = strlen(compressor);
 	if (sz > 0 && compressor[sz - 1] == '\n')
 		compressor[sz - 1] = 0x00;
 
-	if (!zcomp_available_algorithm(compressor))
+	if (!zcomp_available_algorithm(compressor)) {
+		kfree(compressor);
 		return -EINVAL;
+	}
 
 	down_write(&zram->init_lock);
 	if (init_done(zram)) {
 		up_write(&zram->init_lock);
+		kfree(compressor);
 		pr_info("Can't change algorithm for initialized device\n");
 		return -EBUSY;
 	}
 
-	strcpy(zram->compressor, compressor);
+	comp_algorithm_set(zram, prio, compressor);
 	up_write(&zram->init_lock);
-	return len;
+	return 0;
+}
+
+static ssize_t comp_algorithm_show(struct device *dev,
+				   struct device_attribute *attr,
+				   char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+
+	return __comp_algorithm_show(zram, ZRAM_PRIMARY_COMP, buf);
+}
+
+static ssize_t comp_algorithm_store(struct device *dev,
+				    struct device_attribute *attr,
+				    const char *buf,
+				    size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	int ret;
+
+	ret = __comp_algorithm_store(zram, ZRAM_PRIMARY_COMP, buf);
+	return ret ? ret : len;
+}
+
+#ifdef CONFIG_ZRAM_MULTI_COMP
+static ssize_t recomp_algorithm_show(struct device *dev,
+				     struct device_attribute *attr,
+				     char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+	ssize_t sz = 0;
+	u32 prio;
+
+	for (prio = ZRAM_SECONDARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
+		if (!zram->comp_algs[prio])
+			continue;
+
+		sz += scnprintf(buf + sz, PAGE_SIZE - sz - 2, "#%d: ", prio);
+		sz += __comp_algorithm_show(zram, prio, buf + sz);
+	}
+
+	return sz;
 }
 
+static ssize_t recomp_algorithm_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf,
+				      size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	int prio = ZRAM_SECONDARY_COMP;
+	char *args, *param, *val;
+	char *alg = NULL;
+	int ret;
+
+	args = skip_spaces(buf);
+	while (*args) {
+		args = next_arg(args, &param, &val);
+
+		if (!val || !*val)
+			return -EINVAL;
+
+		if (!strcmp(param, "algo")) {
+			alg = val;
+			continue;
+		}
+
+		if (!strcmp(param, "priority")) {
+			ret = kstrtoint(val, 10, &prio);
+			if (ret)
+				return ret;
+			continue;
+		}
+	}
+
+	if (!alg)
+		return -EINVAL;
+
+	if (prio < ZRAM_SECONDARY_COMP || prio >= ZRAM_MAX_COMPS)
+		return -EINVAL;
+
+	ret = __comp_algorithm_store(zram, prio, alg);
+	return ret ? ret : len;
+}
+#endif
+
 static ssize_t compact_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
@@ -1058,6 +1200,30 @@ static ssize_t compact_store(struct device *dev,
 	return len;
 }
 
+static int zram_do_scan(struct zram *zram);
+
+static ssize_t merge_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	int ret;
+
+	down_read(&zram->init_lock);
+	if (!init_done(zram)) {
+		up_read(&zram->init_lock);
+		return -EINVAL;
+	}
+
+	ret = zram_do_scan(zram);
+	if (ret != 0) {
+		up_read(&zram->init_lock);
+		return -ENOMEM;
+	}
+
+	up_read(&zram->init_lock);
+	return len;
+}
+
 static ssize_t io_stat_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
@@ -1097,7 +1263,7 @@ 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 %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,
@@ -1106,7 +1272,8 @@ static ssize_t mm_stat_show(struct device *dev,
 			(u64)atomic64_read(&zram->stats.same_pages),
 			atomic_long_read(&pool_stats.pages_compacted),
 			(u64)atomic64_read(&zram->stats.huge_pages),
-			(u64)atomic64_read(&zram->stats.huge_pages_since));
+			(u64)atomic64_read(&zram->stats.huge_pages_since),
+			(u64)atomic64_read(&zram->stats.pages_merged));
 	up_read(&zram->init_lock);
 
 	return ret;
@@ -1157,6 +1324,248 @@ static DEVICE_ATTR_RO(bd_stat);
 #endif
 static DEVICE_ATTR_RO(debug_stat);
 
+static bool zram_rbtree_insert(struct rb_root *root, struct zram_rbtree_node *data)
+{
+	struct rb_node **new = &(root->rb_node), *parent = NULL;
+	struct zram_rbtree_node *this;
+
+	while (*new) {
+		this = rb_entry(*new, struct zram_rbtree_node, node);
+		parent = *new;
+		if (data->key < this->key)
+			new = &((*new)->rb_left);
+		else if (data->key > this->key)
+			new = &((*new)->rb_right);
+		else
+			return false;
+	}
+
+	rb_link_node(&data->node, parent, new);
+	rb_insert_color(&data->node, root);
+	return true;
+}
+
+static struct zram_rbtree_node *zram_rbtree_search(struct rb_root *root,
+		unsigned long key)
+{
+	struct rb_node *node = root->rb_node;
+	struct zram_rbtree_node *data;
+
+	while (node) {
+		data = rb_entry(node, struct zram_rbtree_node, node);
+		if (key < data->key)
+			node = node->rb_left;
+		else if (key > data->key)
+			node = node->rb_right;
+		else
+			return data;
+	}
+
+	return NULL;
+}
+
+static unsigned long zram_calc_hash(void *src, size_t len)
+{
+	return xxhash(src, len, 0);
+}
+
+static int zram_cmp_obj_and_merge(struct zram *zram, struct hlist_head *htable,
+		size_t htable_size, size_t index)
+{
+	struct zram_rbtree_node *rb_node;
+	struct zram_hash_node *node;
+	unsigned long handle, cur_handle;
+	size_t obj_size;
+	char *src, *buf;
+	unsigned long hash;
+	int ret = 0;
+
+	handle = zram_get_handle(zram, index);
+	if (!handle)
+		return ret;
+
+	obj_size = zram_get_obj_size(zram, index);
+	buf = kmalloc(obj_size, GFP_KERNEL);
+	if (!buf) {
+		pr_err("Failed to allocate zs_map_object buffer\n");
+		return -ENOMEM;
+	}
+
+	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
+	memcpy(buf, src, obj_size);
+	zs_unmap_object(zram->mem_pool, handle);
+	hash = zram_calc_hash(buf, obj_size);
+
+	mutex_lock(&zram_rbtree_mutex);
+	hlist_for_each_entry(node, &htable[hash % htable_size], next) {
+		int cmp;
+
+		zram_slot_lock(zram, node->index);
+
+		/*
+		 * Page may change as the hash table is being formed,
+		 * so the checks below are necessary.
+		 */
+		cur_handle = zram_get_handle(zram, node->index);
+		if (handle == cur_handle ||
+			obj_size != zram_get_obj_size(zram, node->index)) {
+			zram_slot_unlock(zram, node->index);
+			continue;
+		}
+
+		src = zs_map_object(zram->mem_pool, cur_handle, ZS_MM_RO);
+		cmp = memcmp(buf, src, obj_size);
+		zs_unmap_object(zram->mem_pool, cur_handle);
+
+		if (!cmp) {
+			rb_node = zram_rbtree_search(&zram->sph_rbtree, handle);
+
+			/*
+			 * This check is necessary in order not to zs_free an object
+			 * that someone already refers to. This situation is possible
+			 * when with repeated calls to zram_do_scan(). For example:
+			 *
+			 * [slot0] [slot1] [slot2] [slot3] [slot4]
+			 * [obj0]  [obj1]  [obj2]  [obj3]  [obj4]
+			 *
+			 * Let's imagine that obj2 and obj3 are equal, and we called
+			 * zram_do_scan() function:
+			 *
+			 * [slot0] [slot1] [slot2] [slot3] [slot4]
+			 * [obj0]  [obj1]  [obj2]  [obj2]  [obj4]
+			 *
+			 * Now, slot2 and slot3 refers to obj2 zsmalloc object.
+			 * Time passed, now slot0 refres to obj0_n, which is equal
+			 * to obj2:
+			 *
+			 * [slot0]  [slot1] [slot2] [slot3] [slot4]
+			 * [obj0_n] [obj1]  [obj2]  [obj2]  [obj4]
+			 *
+			 * Now we call zram_do_scan() function again. We get to slot2,
+			 * and we understand that obj2 and obj0_n hashes are the same. We
+			 * try to zs_free(obj2), but slot3 also already refers to it.
+			 *
+			 * This is not correct!
+			 */
+			if (unlikely(rb_node))
+				if (rb_node->cnt > 1) {
+					zram_slot_unlock(zram, node->index);
+					continue;
+				}
+
+			zram_set_handle(zram, index, cur_handle);
+			zs_free(zram->mem_pool, handle);
+
+			rb_node = zram_rbtree_search(&zram->sph_rbtree, cur_handle);
+
+			if (!rb_node) {
+				rb_node = kzalloc(sizeof(struct zram_rbtree_node),
+								GFP_KERNEL);
+				if (!rb_node) {
+					pr_err("Failed to allocate rb_node\n");
+					ret = -ENOMEM;
+					zram_slot_unlock(zram, node->index);
+					mutex_unlock(&zram_rbtree_mutex);
+					goto merged_or_err;
+				}
+
+				rb_node->key = cur_handle;
+				/* Two slots refers to an zsmalloc object with cur_handle key */
+				rb_node->cnt = 2;
+				zram_rbtree_insert(&zram->sph_rbtree, rb_node);
+			} else {
+				rb_node->cnt++;
+			}
+
+			atomic64_inc(&zram->stats.pages_merged);
+			atomic64_sub(obj_size, &zram->stats.compr_data_size);
+			zram_set_flag(zram, index, ZRAM_MERGED);
+			zram_set_flag(zram, node->index, ZRAM_MERGED);
+
+			zram_slot_unlock(zram, node->index);
+			mutex_unlock(&zram_rbtree_mutex);
+			goto merged_or_err;
+		}
+
+		zram_slot_unlock(zram, node->index);
+	}
+
+	mutex_unlock(&zram_rbtree_mutex);
+
+	node = kmalloc(sizeof(struct zram_hash_node), GFP_KERNEL);
+	if (!node) {
+		ret = -ENOMEM;
+		goto merged_or_err;
+	}
+
+	node->index = index;
+	hlist_add_head(&node->next, &htable[hash % htable_size]);
+
+merged_or_err:
+	kfree(buf);
+	return ret;
+}
+
+static void zram_free_htable_entries(struct hlist_head *htable,
+		size_t htable_size)
+{
+	struct hlist_node *n;
+	struct zram_hash_node *node;
+
+	hlist_for_each_entry_safe(node, n, htable, next) {
+		hlist_del(&node->next);
+		kfree(node);
+	}
+}
+
+static int zram_do_scan(struct zram *zram)
+{
+	size_t num_pages = zram->disksize >> PAGE_SHIFT;
+	size_t htable_size = num_pages;
+	size_t index;
+	struct hlist_head *htable;
+	int i, ret = 0;
+
+	htable = vzalloc(htable_size * sizeof(struct hlist_head));
+	if (!htable) {
+		pr_err("Failed to allocate hash table\n");
+		return -ENOMEM;
+	}
+
+	for (i = 0; i < htable_size; i++)
+		INIT_HLIST_HEAD(&htable[i]);
+
+	for (index = 0; index < num_pages; index++) {
+		zram_slot_lock(zram, index);
+
+		if (!zram_allocated(zram, index)) {
+			zram_slot_unlock(zram, index);
+			continue;
+		}
+
+		if (zram_test_flag(zram, index, ZRAM_UNDER_WB) ||
+			zram_test_flag(zram, index, ZRAM_WB) ||
+			zram_test_flag(zram, index, ZRAM_SAME)) {
+			zram_slot_unlock(zram, index);
+			continue;
+		}
+
+		/* Ignore pages that have been recompressed */
+		if (zram_get_priority(zram, index) != 0)
+			continue;
+
+		ret = zram_cmp_obj_and_merge(zram, htable, htable_size, index);
+		zram_slot_unlock(zram, index);
+		if (ret != 0)
+			goto out;
+	}
+
+out:
+	zram_free_htable_entries(htable, htable_size);
+	vfree(htable);
+	return ret;
+}
+
 static void zram_meta_free(struct zram *zram, u64 disksize)
 {
 	size_t num_pages = disksize >> PAGE_SHIFT;
@@ -1198,6 +1607,7 @@ 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_rbtree_node *node;
 
 #ifdef CONFIG_ZRAM_MEMORY_TRACKING
 	zram->table[index].ac_time = 0;
@@ -1210,6 +1620,11 @@ static void zram_free_page(struct zram *zram, size_t index)
 		atomic64_dec(&zram->stats.huge_pages);
 	}
 
+	if (zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE))
+		zram_clear_flag(zram, index, ZRAM_INCOMPRESSIBLE);
+
+	zram_set_priority(zram, index, 0);
+
 	if (zram_test_flag(zram, index, ZRAM_WB)) {
 		zram_clear_flag(zram, index, ZRAM_WB);
 		free_block_bdev(zram, zram_get_element(zram, index));
@@ -1230,7 +1645,28 @@ static void zram_free_page(struct zram *zram, size_t index)
 	if (!handle)
 		return;
 
-	zs_free(zram->mem_pool, handle);
+	if (zram_test_flag(zram, index, ZRAM_MERGED)) {
+		zram_clear_flag(zram, index, ZRAM_MERGED);
+		mutex_lock(&zram_rbtree_mutex);
+
+		node = zram_rbtree_search(&zram->sph_rbtree, handle);
+		BUG_ON(!node);
+
+		node->cnt--;
+		if (node->cnt == 0) {
+			rb_erase(&node->node, &zram->sph_rbtree);
+			mutex_unlock(&zram_rbtree_mutex);
+
+			zs_free(zram->mem_pool, handle);
+			kfree(node);
+		} else {
+			mutex_unlock(&zram_rbtree_mutex);
+		}
+
+		atomic64_dec(&zram->stats.pages_merged);
+	} else {
+		zs_free(zram->mem_pool, handle);
+	}
 
 	atomic64_sub(zram_get_obj_size(zram, index),
 			&zram->stats.compr_data_size);
@@ -1242,32 +1678,37 @@ static void zram_free_page(struct zram *zram, size_t index)
 		~(1UL << ZRAM_LOCK | 1UL << ZRAM_UNDER_WB));
 }
 
-static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
-				struct bio *bio, bool partial_io)
+/*
+ * Reads a page from the writeback devices. Corresponding ZRAM slot
+ * should be unlocked.
+ */
+static int zram_bvec_read_from_bdev(struct zram *zram, struct page *page,
+				    u32 index, struct bio *bio, bool partial_io)
+{
+	struct bio_vec bvec = {
+		.bv_page = page,
+		.bv_len = PAGE_SIZE,
+		.bv_offset = 0,
+	};
+
+	return read_from_bdev(zram, &bvec, zram_get_element(zram, index), bio,
+			      partial_io);
+}
+
+/*
+ * Reads (decompresses if needed) a page from zspool (zsmalloc).
+ * Corresponding ZRAM slot should be locked.
+ */
+static int zram_read_from_zspool(struct zram *zram, struct page *page,
+				 u32 index)
 {
 	struct zcomp_strm *zstrm;
 	unsigned long handle;
 	unsigned int size;
 	void *src, *dst;
+	u32 prio;
 	int ret;
 
-	zram_slot_lock(zram, index);
-	if (zram_test_flag(zram, index, ZRAM_WB)) {
-		struct bio_vec bvec;
-
-		zram_slot_unlock(zram, index);
-		/* A null bio means rw_page was used, we must fallback to bio */
-		if (!bio)
-			return -EOPNOTSUPP;
-
-		bvec.bv_page = page;
-		bvec.bv_len = PAGE_SIZE;
-		bvec.bv_offset = 0;
-		return read_from_bdev(zram, &bvec,
-				zram_get_element(zram, index),
-				bio, partial_io);
-	}
-
 	handle = zram_get_handle(zram, index);
 	if (!handle || zram_test_flag(zram, index, ZRAM_SAME)) {
 		unsigned long value;
@@ -1277,14 +1718,15 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 		mem = kmap_atomic(page);
 		zram_fill_page(mem, PAGE_SIZE, value);
 		kunmap_atomic(mem);
-		zram_slot_unlock(zram, index);
 		return 0;
 	}
 
 	size = zram_get_obj_size(zram, index);
 
-	if (size != PAGE_SIZE)
-		zstrm = zcomp_stream_get(zram->comp);
+	if (size != PAGE_SIZE) {
+		prio = zram_get_priority(zram, index);
+		zstrm = zcomp_stream_get(zram->comps[prio]);
+	}
 
 	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
 	if (size == PAGE_SIZE) {
@@ -1296,20 +1738,43 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 		dst = kmap_atomic(page);
 		ret = zcomp_decompress(zstrm, src, size, dst);
 		kunmap_atomic(dst);
-		zcomp_stream_put(zram->comp);
+		zcomp_stream_put(zram->comps[prio]);
 	}
 	zs_unmap_object(zram->mem_pool, handle);
-	zram_slot_unlock(zram, index);
+	return ret;
+}
+
+static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
+			    struct bio *bio, bool partial_io)
+{
+	int ret;
+
+	zram_slot_lock(zram, index);
+	if (!zram_test_flag(zram, index, ZRAM_WB)) {
+		/* Slot should be locked through out the function call */
+		ret = zram_read_from_zspool(zram, page, index);
+		zram_slot_unlock(zram, index);
+	} else {
+		/* Slot should be unlocked before the function call */
+		zram_slot_unlock(zram, index);
+
+		/* A null bio means rw_page was used, we must fallback to bio */
+		if (!bio)
+			return -EOPNOTSUPP;
+
+		ret = zram_bvec_read_from_bdev(zram, page, index, bio,
+					       partial_io);
+	}
 
 	/* Should NEVER happen. Return bio error if it does. */
-	if (WARN_ON(ret))
+	if (WARN_ON(ret < 0))
 		pr_err("Decompression failed! err=%d, page=%u\n", ret, index);
 
 	return ret;
 }
 
 static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
-				u32 index, int offset, struct bio *bio)
+			  u32 index, int offset, struct bio *bio)
 {
 	int ret;
 	struct page *page;
@@ -1363,13 +1828,13 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 	kunmap_atomic(mem);
 
 compress_again:
-	zstrm = zcomp_stream_get(zram->comp);
+	zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
 	src = kmap_atomic(page);
 	ret = zcomp_compress(zstrm, src, &comp_len);
 	kunmap_atomic(src);
 
 	if (unlikely(ret)) {
-		zcomp_stream_put(zram->comp);
+		zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
 		pr_err("Compression failed! err=%d\n", ret);
 		zs_free(zram->mem_pool, handle);
 		return ret;
@@ -1390,19 +1855,19 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 	 * if we have a 'non-null' handle here then we are coming
 	 * from the slow path and handle has already been allocated.
 	 */
-	if (IS_ERR((void *)handle))
+	if (IS_ERR_VALUE(handle))
 		handle = zs_malloc(zram->mem_pool, comp_len,
 				__GFP_KSWAPD_RECLAIM |
 				__GFP_NOWARN |
 				__GFP_HIGHMEM |
 				__GFP_MOVABLE);
-	if (IS_ERR((void *)handle)) {
-		zcomp_stream_put(zram->comp);
+	if (IS_ERR_VALUE(handle)) {
+		zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
 		atomic64_inc(&zram->stats.writestall);
 		handle = zs_malloc(zram->mem_pool, comp_len,
 				GFP_NOIO | __GFP_HIGHMEM |
 				__GFP_MOVABLE);
-		if (IS_ERR((void *)handle))
+		if (IS_ERR_VALUE(handle))
 			return PTR_ERR((void *)handle);
 
 		if (comp_len != PAGE_SIZE)
@@ -1414,14 +1879,14 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 		 * zstrm buffer back. It is necessary that the dereferencing
 		 * of the zstrm variable below occurs correctly.
 		 */
-		zstrm = zcomp_stream_get(zram->comp);
+		zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
 	}
 
 	alloced_pages = zs_get_total_pages(zram->mem_pool);
 	update_used_max(zram, alloced_pages);
 
 	if (zram->limit_pages && alloced_pages > zram->limit_pages) {
-		zcomp_stream_put(zram->comp);
+		zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
 		zs_free(zram->mem_pool, handle);
 		return -ENOMEM;
 	}
@@ -1435,7 +1900,7 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 	if (comp_len == PAGE_SIZE)
 		kunmap_atomic(src);
 
-	zcomp_stream_put(zram->comp);
+	zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
 	zs_unmap_object(zram->mem_pool, handle);
 	atomic64_add(comp_len, &zram->stats.compr_data_size);
 out:
@@ -1504,6 +1969,276 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 	return ret;
 }
 
+#ifdef CONFIG_ZRAM_MULTI_COMP
+/*
+ * This function will decompress (unless it's ZRAM_HUGE) the page and then
+ * attempt to compress it using provided compression algorithm priority
+ * (which is potentially more effective).
+ *
+ * Corresponding ZRAM slot should be locked.
+ */
+static int zram_recompress(struct zram *zram, u32 index, struct page *page,
+			   u32 threshold, u32 prio, u32 prio_max)
+{
+	struct zcomp_strm *zstrm = NULL;
+	unsigned long handle_old;
+	unsigned long handle_new;
+	unsigned int comp_len_old;
+	unsigned int comp_len_new;
+	unsigned int class_index_old;
+	unsigned int class_index_new;
+	u32 num_recomps = 0;
+	void *src, *dst;
+	int ret;
+
+	handle_old = zram_get_handle(zram, index);
+	if (!handle_old)
+		return -EINVAL;
+
+	comp_len_old = zram_get_obj_size(zram, index);
+	/*
+	 * Do not recompress objects that are already "small enough".
+	 */
+	if (comp_len_old < threshold)
+		return 0;
+
+	ret = zram_read_from_zspool(zram, page, index);
+	if (ret)
+		return ret;
+
+	class_index_old = zs_lookup_class_index(zram->mem_pool, comp_len_old);
+	/*
+	 * Iterate the secondary comp algorithms list (in order of priority)
+	 * and try to recompress the page.
+	 */
+	prio_max = min(prio_max, ZRAM_MAX_COMPS);
+	for (; prio < prio_max; prio++) {
+		if (!zram->comps[prio])
+			continue;
+
+		/*
+		 * Skip if the object is already re-compressed with a higher
+		 * priority algorithm (or same algorithm).
+		 */
+		if (prio <= zram_get_priority(zram, index))
+			continue;
+
+		num_recomps++;
+		zstrm = zcomp_stream_get(zram->comps[prio]);
+		src = kmap_atomic(page);
+		ret = zcomp_compress(zstrm, src, &comp_len_new);
+		kunmap_atomic(src);
+
+		if (ret) {
+			zcomp_stream_put(zram->comps[prio]);
+			return ret;
+		}
+
+		class_index_new = zs_lookup_class_index(zram->mem_pool,
+							comp_len_new);
+
+		/* Continue until we make progress */
+		if (class_index_new >= class_index_old ||
+		    (threshold && comp_len_new >= threshold)) {
+			zcomp_stream_put(zram->comps[prio]);
+			continue;
+		}
+
+		/* Recompression was successful so break out */
+		break;
+	}
+
+	/*
+	 * We did not try to recompress, e.g. when we have only one
+	 * secondary algorithm and the page is already recompressed
+	 * using that algorithm
+	 */
+	if (!zstrm)
+		return 0;
+
+	if (class_index_new >= class_index_old) {
+		/*
+		 * Secondary algorithms failed to re-compress the page
+		 * in a way that would save memory, mark the object as
+		 * incompressible so that we will not try to compress
+		 * it again.
+		 *
+		 * We need to make sure that all secondary algorithms have
+		 * failed, so we test if the number of recompressions matches
+		 * the number of active secondary algorithms.
+		 */
+		if (num_recomps == zram->num_active_comps - 1)
+			zram_set_flag(zram, index, ZRAM_INCOMPRESSIBLE);
+		return 0;
+	}
+
+	/* Successful recompression but above threshold */
+	if (threshold && comp_len_new >= threshold)
+		return 0;
+
+	/*
+	 * No direct reclaim (slow path) for handle allocation and no
+	 * re-compression attempt (unlike in __zram_bvec_write()) since
+	 * we already have stored that object in zsmalloc. If we cannot
+	 * alloc memory for recompressed object then we bail out and
+	 * simply keep the old (existing) object in zsmalloc.
+	 */
+	handle_new = zs_malloc(zram->mem_pool, comp_len_new,
+			       __GFP_KSWAPD_RECLAIM |
+			       __GFP_NOWARN |
+			       __GFP_HIGHMEM |
+			       __GFP_MOVABLE);
+	if (IS_ERR_VALUE(handle_new)) {
+		zcomp_stream_put(zram->comps[prio]);
+		return PTR_ERR((void *)handle_new);
+	}
+
+	dst = zs_map_object(zram->mem_pool, handle_new, ZS_MM_WO);
+	memcpy(dst, zstrm->buffer, comp_len_new);
+	zcomp_stream_put(zram->comps[prio]);
+
+	zs_unmap_object(zram->mem_pool, handle_new);
+
+	zram_free_page(zram, index);
+	zram_set_handle(zram, index, handle_new);
+	zram_set_obj_size(zram, index, comp_len_new);
+	zram_set_priority(zram, index, prio);
+
+	atomic64_add(comp_len_new, &zram->stats.compr_data_size);
+	atomic64_inc(&zram->stats.pages_stored);
+
+	return 0;
+}
+
+#define RECOMPRESS_IDLE		(1 << 0)
+#define RECOMPRESS_HUGE		(1 << 1)
+
+static ssize_t recompress_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t len)
+{
+	u32 prio = ZRAM_SECONDARY_COMP, prio_max = ZRAM_MAX_COMPS;
+	struct zram *zram = dev_to_zram(dev);
+	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
+	char *args, *param, *val, *algo = NULL;
+	u32 mode = 0, threshold = 0;
+	unsigned long index;
+	struct page *page;
+	ssize_t ret;
+
+	args = skip_spaces(buf);
+	while (*args) {
+		args = next_arg(args, &param, &val);
+
+		if (!val || !*val)
+			return -EINVAL;
+
+		if (!strcmp(param, "type")) {
+			if (!strcmp(val, "idle"))
+				mode = RECOMPRESS_IDLE;
+			if (!strcmp(val, "huge"))
+				mode = RECOMPRESS_HUGE;
+			if (!strcmp(val, "huge_idle"))
+				mode = RECOMPRESS_IDLE | RECOMPRESS_HUGE;
+			continue;
+		}
+
+		if (!strcmp(param, "threshold")) {
+			/*
+			 * We will re-compress only idle objects equal or
+			 * greater in size than watermark.
+			 */
+			ret = kstrtouint(val, 10, &threshold);
+			if (ret)
+				return ret;
+			continue;
+		}
+
+		if (!strcmp(param, "algo")) {
+			algo = val;
+			continue;
+		}
+	}
+
+	if (threshold >= PAGE_SIZE)
+		return -EINVAL;
+
+	down_read(&zram->init_lock);
+	if (!init_done(zram)) {
+		ret = -EINVAL;
+		goto release_init_lock;
+	}
+
+	if (algo) {
+		bool found = false;
+
+		for (; prio < ZRAM_MAX_COMPS; prio++) {
+			if (!zram->comp_algs[prio])
+				continue;
+
+			if (!strcmp(zram->comp_algs[prio], algo)) {
+				prio_max = min(prio + 1, ZRAM_MAX_COMPS);
+				found = true;
+				break;
+			}
+		}
+
+		if (!found) {
+			ret = -EINVAL;
+			goto release_init_lock;
+		}
+	}
+
+	page = alloc_page(GFP_KERNEL);
+	if (!page) {
+		ret = -ENOMEM;
+		goto release_init_lock;
+	}
+
+	ret = len;
+	for (index = 0; index < nr_pages; index++) {
+		int err = 0;
+
+		zram_slot_lock(zram, index);
+
+		if (!zram_allocated(zram, index))
+			goto next;
+
+		if (mode & RECOMPRESS_IDLE &&
+		    !zram_test_flag(zram, index, ZRAM_IDLE))
+			goto next;
+
+		if (mode & RECOMPRESS_HUGE &&
+		    !zram_test_flag(zram, index, ZRAM_HUGE))
+			goto next;
+
+		if (zram_test_flag(zram, index, ZRAM_WB) ||
+		    zram_test_flag(zram, index, ZRAM_UNDER_WB) ||
+		    zram_test_flag(zram, index, ZRAM_SAME) ||
+		    zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE) ||
+		    zram_test_flag(zram, index, ZRAM_MERGED))
+			goto next;
+
+		err = zram_recompress(zram, index, page, threshold,
+				      prio, prio_max);
+next:
+		zram_slot_unlock(zram, index);
+		if (err) {
+			ret = err;
+			break;
+		}
+
+		cond_resched();
+	}
+
+	__free_page(page);
+
+release_init_lock:
+	up_read(&zram->init_lock);
+	return ret;
+}
+#endif
+
 /*
  * zram_bio_discard - handler on discard request
  * @index: physical block index in PAGE_SIZE units
@@ -1710,6 +2445,21 @@ static int zram_rw_page(struct block_device *bdev, sector_t sector,
 	return ret;
 }
 
+static void zram_destroy_comps(struct zram *zram)
+{
+	u32 prio;
+
+	for (prio = 0; prio < ZRAM_MAX_COMPS; prio++) {
+		struct zcomp *comp = zram->comps[prio];
+
+		zram->comps[prio] = NULL;
+		if (!comp)
+			continue;
+		zcomp_destroy(comp);
+		zram->num_active_comps--;
+	}
+}
+
 static void zram_reset_device(struct zram *zram)
 {
 	down_write(&zram->init_lock);
@@ -1727,11 +2477,11 @@ static void zram_reset_device(struct zram *zram)
 	/* I/O operation under all of CPU are done so let's free */
 	zram_meta_free(zram, zram->disksize);
 	zram->disksize = 0;
+	zram_destroy_comps(zram);
 	memset(&zram->stats, 0, sizeof(zram->stats));
-	zcomp_destroy(zram->comp);
-	zram->comp = NULL;
 	reset_bdev(zram);
 
+	comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);
 	up_write(&zram->init_lock);
 }
 
@@ -1742,6 +2492,7 @@ static ssize_t disksize_store(struct device *dev,
 	struct zcomp *comp;
 	struct zram *zram = dev_to_zram(dev);
 	int err;
+	u32 prio;
 
 	disksize = memparse(buf, NULL);
 	if (!disksize)
@@ -1760,22 +2511,29 @@ static ssize_t disksize_store(struct device *dev,
 		goto out_unlock;
 	}
 
-	comp = zcomp_create(zram->compressor);
-	if (IS_ERR(comp)) {
-		pr_err("Cannot initialise %s compressing backend\n",
-				zram->compressor);
-		err = PTR_ERR(comp);
-		goto out_free_meta;
-	}
+	for (prio = 0; prio < ZRAM_MAX_COMPS; prio++) {
+		if (!zram->comp_algs[prio])
+			continue;
 
-	zram->comp = comp;
+		comp = zcomp_create(zram->comp_algs[prio]);
+		if (IS_ERR(comp)) {
+			pr_err("Cannot initialise %s compressing backend\n",
+			       zram->comp_algs[prio]);
+			err = PTR_ERR(comp);
+			goto out_free_comps;
+		}
+
+		zram->comps[prio] = comp;
+		zram->num_active_comps++;
+	}
 	zram->disksize = disksize;
 	set_capacity_and_notify(zram->disk, zram->disksize >> SECTOR_SHIFT);
 	up_write(&zram->init_lock);
 
 	return len;
 
-out_free_meta:
+out_free_comps:
+	zram_destroy_comps(zram);
 	zram_meta_free(zram, disksize);
 out_unlock:
 	up_write(&zram->init_lock);
@@ -1846,6 +2604,7 @@ static const struct block_device_operations zram_devops = {
 };
 
 static DEVICE_ATTR_WO(compact);
+static DEVICE_ATTR_WO(merge);
 static DEVICE_ATTR_RW(disksize);
 static DEVICE_ATTR_RO(initstate);
 static DEVICE_ATTR_WO(reset);
@@ -1860,6 +2619,10 @@ static DEVICE_ATTR_WO(writeback);
 static DEVICE_ATTR_RW(writeback_limit);
 static DEVICE_ATTR_RW(writeback_limit_enable);
 #endif
+#ifdef CONFIG_ZRAM_MULTI_COMP
+static DEVICE_ATTR_RW(recomp_algorithm);
+static DEVICE_ATTR_WO(recompress);
+#endif
 
 static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_disksize.attr,
@@ -1882,7 +2645,12 @@ static struct attribute *zram_disk_attrs[] = {
 #ifdef CONFIG_ZRAM_WRITEBACK
 	&dev_attr_bd_stat.attr,
 #endif
+	&dev_attr_merge.attr,
 	&dev_attr_debug_stat.attr,
+#ifdef CONFIG_ZRAM_MULTI_COMP
+	&dev_attr_recomp_algorithm.attr,
+	&dev_attr_recompress.attr,
+#endif
 	NULL,
 };
 
@@ -1962,7 +2730,9 @@ static int zram_add(void)
 	if (ret)
 		goto out_cleanup_disk;
 
-	strscpy(zram->compressor, default_compressor, sizeof(zram->compressor));
+	comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);
+
+	zram->sph_rbtree = RB_ROOT;
 
 	zram_debugfs_register(zram);
 	pr_info("Added device: %s\n", zram->disk->disk_name);
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index a2bda53020fd..6b3bc216baa3 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -40,6 +40,9 @@
  */
 #define ZRAM_FLAG_SHIFT (PAGE_SHIFT + 1)
 
+/* Only 2 bits are allowed for comp priority index */
+#define ZRAM_COMP_PRIORITY_MASK	0x3
+
 /* Flags for zram pages (table[page_no].flags) */
 enum zram_pageflags {
 	/* zram slot is locked */
@@ -49,6 +52,11 @@ enum zram_pageflags {
 	ZRAM_UNDER_WB,	/* page is under writeback */
 	ZRAM_HUGE,	/* Incompressible page */
 	ZRAM_IDLE,	/* not accessed page since last idle marking */
+	ZRAM_INCOMPRESSIBLE, /* none of the algorithms could compress it */
+
+	ZRAM_COMP_PRIORITY_BIT1, /* First bit of comp priority index */
+	ZRAM_COMP_PRIORITY_BIT2, /* Second bit of comp priority index */
+	ZRAM_MERGED,	/* page was merged */
 
 	__NR_ZRAM_PAGEFLAGS,
 };
@@ -82,6 +90,7 @@ struct zram_stats {
 	atomic_long_t max_used_pages;	/* no. of maximum pages stored */
 	atomic64_t writestall;		/* no. of write slow paths */
 	atomic64_t miss_free;		/* no. of missed free */
+	atomic64_t pages_merged;	/* no. of pages, which merged into single one */
 #ifdef	CONFIG_ZRAM_WRITEBACK
 	atomic64_t bd_count;		/* no. of pages in backing device */
 	atomic64_t bd_reads;		/* no. of reads from backing device */
@@ -89,10 +98,20 @@ struct zram_stats {
 #endif
 };
 
+#ifdef CONFIG_ZRAM_MULTI_COMP
+#define ZRAM_PRIMARY_COMP	0U
+#define ZRAM_SECONDARY_COMP	1U
+#define ZRAM_MAX_COMPS	4U
+#else
+#define ZRAM_PRIMARY_COMP	0U
+#define ZRAM_SECONDARY_COMP	0U
+#define ZRAM_MAX_COMPS	1U
+#endif
+
 struct zram {
 	struct zram_table_entry *table;
 	struct zs_pool *mem_pool;
-	struct zcomp *comp;
+	struct zcomp *comps[ZRAM_MAX_COMPS];
 	struct gendisk *disk;
 	/* Prevent concurrent execution of device init */
 	struct rw_semaphore init_lock;
@@ -107,7 +126,8 @@ struct zram {
 	 * we can store in a disk.
 	 */
 	u64 disksize;	/* bytes */
-	char compressor[CRYPTO_MAX_ALG_NAME];
+	const char *comp_algs[ZRAM_MAX_COMPS];
+	s8 num_active_comps;
 	/*
 	 * zram is claimed so open request will be failed
 	 */
@@ -124,5 +144,10 @@ struct zram {
 #ifdef CONFIG_ZRAM_MEMORY_TRACKING
 	struct dentry *debugfs_dir;
 #endif
+	/*
+	 * This is same pages handle's rb tree, where the key is a handle
+	 * to same pages and the value is a link counter
+	 */
+	struct rb_root sph_rbtree;
 };
 #endif
diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h
index 2a430e713ce5..a48cd0ffe57d 100644
--- a/include/linux/zsmalloc.h
+++ b/include/linux/zsmalloc.h
@@ -55,5 +55,7 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle);
 unsigned long zs_get_total_pages(struct zs_pool *pool);
 unsigned long zs_compact(struct zs_pool *pool);
 
+unsigned int zs_lookup_class_index(struct zs_pool *pool, unsigned int size);
+
 void zs_pool_stats(struct zs_pool *pool, struct zs_pool_stats *stats);
 #endif
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 56f58a96b129..90394e3f3892 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1205,6 +1205,27 @@ static bool zspage_full(struct size_class *class, struct zspage *zspage)
 	return get_zspage_inuse(zspage) == class->objs_per_zspage;
 }
 
+/**
+ * zs_lookup_class_index() - Returns index of the zsmalloc &size_class
+ * that hold objects of the provided size.
+ * @pool: zsmalloc pool to use
+ * @size: object size
+ *
+ * Context: Any context.
+ *
+ * Return: the index of the zsmalloc &size_class that hold objects of the
+ * provided size.
+ */
+unsigned int zs_lookup_class_index(struct zs_pool *pool, unsigned int size)
+{
+	struct size_class *class;
+
+	class = pool->size_class[get_size_class_index(size)];
+
+	return class->index;
+}
+EXPORT_SYMBOL_GPL(zs_lookup_class_index);
+
 unsigned long zs_get_total_pages(struct zs_pool *pool)
 {
 	return atomic_long_read(&pool->pages_allocated);
-- 
2.40.0