Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

6 files changed, 2602 insertions, 0 deletions

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
new file mode 100644
index 000000000..fe7a4b7d3
--- /dev/null
+++ b/drivers/block/zram/Kconfig
@@ -0,0 +1,39 @@
+# SPDX-License-Identifier: GPL-2.0
+config ZRAM
+	tristate "Compressed RAM block device support"
+	depends on BLOCK && SYSFS && ZSMALLOC && CRYPTO
+	select CRYPTO_LZO
+	help
+	  Creates virtual block devices called /dev/zramX (X = 0, 1, ...).
+	  Pages written to these disks are compressed and stored in memory
+	  itself. These disks allow very fast I/O and compression provides
+	  good amounts of memory savings.
+
+	  It has several use cases, for example: /tmp storage, use as swap
+	  disks and maybe many more.
+
+	  See Documentation/admin-guide/blockdev/zram.rst for more information.
+
+config ZRAM_WRITEBACK
+       bool "Write back incompressible or idle page to backing device"
+       depends on ZRAM
+       help
+	 With incompressible page, there is no memory saving to keep it
+	 in memory. Instead, write it out to backing device.
+	 For this feature, admin should set up backing device via
+	 /sys/block/zramX/backing_dev.
+
+	 With /sys/block/zramX/{idle,writeback}, application could ask
+	 idle page's writeback to the backing device to save in memory.
+
+	 See Documentation/admin-guide/blockdev/zram.rst for more information.
+
+config ZRAM_MEMORY_TRACKING
+	bool "Track zRam block status"
+	depends on ZRAM && DEBUG_FS
+	help
+	  With this feature, admin can track the state of allocated blocks
+	  of zRAM. Admin could see the information via
+	  /sys/kernel/debug/zram/zramX/block_state.
+
+	  See Documentation/admin-guide/blockdev/zram.rst for more information.
diff --git a/drivers/block/zram/Makefile b/drivers/block/zram/Makefile
new file mode 100644
index 000000000..de9e45790
--- /dev/null
+++ b/drivers/block/zram/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
+zram-y	:=	zcomp.o zram_drv.o
+
+obj-$(CONFIG_ZRAM)	+=	zram.o
diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
new file mode 100644
index 000000000..b08650417
--- /dev/null
+++ b/drivers/block/zram/zcomp.c
@@ -0,0 +1,231 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2014 Sergey Senozhatsky.
+ */
+
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/wait.h>
+#include <linux/sched.h>
+#include <linux/cpu.h>
+#include <linux/crypto.h>
+
+#include "zcomp.h"
+
+static const char * const backends[] = {
+	"lzo",
+	"lzo-rle",
+#if IS_ENABLED(CONFIG_CRYPTO_LZ4)
+	"lz4",
+#endif
+#if IS_ENABLED(CONFIG_CRYPTO_LZ4HC)
+	"lz4hc",
+#endif
+#if IS_ENABLED(CONFIG_CRYPTO_842)
+	"842",
+#endif
+#if IS_ENABLED(CONFIG_CRYPTO_ZSTD)
+	"zstd",
+#endif
+};
+
+static void zcomp_strm_free(struct zcomp_strm *zstrm)
+{
+	if (!IS_ERR_OR_NULL(zstrm->tfm))
+		crypto_free_comp(zstrm->tfm);
+	free_pages((unsigned long)zstrm->buffer, 1);
+	zstrm->tfm = NULL;
+	zstrm->buffer = NULL;
+}
+
+/*
+ * Initialize zcomp_strm structure with ->tfm initialized by backend, and
+ * ->buffer. Return a negative value on error.
+ */
+static int zcomp_strm_init(struct zcomp_strm *zstrm, struct zcomp *comp)
+{
+	zstrm->tfm = crypto_alloc_comp(comp->name, 0, 0);
+	/*
+	 * allocate 2 pages. 1 for compressed data, plus 1 extra for the
+	 * case when compressed size is larger than the original one
+	 */
+	zstrm->buffer = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
+	if (IS_ERR_OR_NULL(zstrm->tfm) || !zstrm->buffer) {
+		zcomp_strm_free(zstrm);
+		return -ENOMEM;
+	}
+	return 0;
+}
+
+bool zcomp_available_algorithm(const char *comp)
+{
+	/*
+	 * Crypto does not ignore a trailing new line symbol,
+	 * so make sure you don't supply a string containing
+	 * one.
+	 * This also means that we permit zcomp initialisation
+	 * with any compressing algorithm known to crypto api.
+	 */
+	return crypto_has_comp(comp, 0, 0) == 1;
+}
+
+/* show available compressors */
+ssize_t zcomp_available_show(const char *comp, char *buf)
+{
+	bool known_algorithm = false;
+	ssize_t sz = 0;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(backends); i++) {
+		if (!strcmp(comp, backends[i])) {
+			known_algorithm = true;
+			sz += scnprintf(buf + sz, PAGE_SIZE - sz - 2,
+					"[%s] ", backends[i]);
+		} else {
+			sz += scnprintf(buf + sz, PAGE_SIZE - sz - 2,
+					"%s ", backends[i]);
+		}
+	}
+
+	/*
+	 * Out-of-tree module known to crypto api or a missing
+	 * entry in `backends'.
+	 */
+	if (!known_algorithm && crypto_has_comp(comp, 0, 0) == 1)
+		sz += scnprintf(buf + sz, PAGE_SIZE - sz - 2,
+				"[%s] ", comp);
+
+	sz += scnprintf(buf + sz, PAGE_SIZE - sz, "\n");
+	return sz;
+}
+
+struct zcomp_strm *zcomp_stream_get(struct zcomp *comp)
+{
+	local_lock(&comp->stream->lock);
+	return this_cpu_ptr(comp->stream);
+}
+
+void zcomp_stream_put(struct zcomp *comp)
+{
+	local_unlock(&comp->stream->lock);
+}
+
+int zcomp_compress(struct zcomp_strm *zstrm,
+		const void *src, unsigned int *dst_len)
+{
+	/*
+	 * Our dst memory (zstrm->buffer) is always `2 * PAGE_SIZE' sized
+	 * because sometimes we can endup having a bigger compressed data
+	 * due to various reasons: for example compression algorithms tend
+	 * to add some padding to the compressed buffer. Speaking of padding,
+	 * comp algorithm `842' pads the compressed length to multiple of 8
+	 * and returns -ENOSP when the dst memory is not big enough, which
+	 * is not something that ZRAM wants to see. We can handle the
+	 * `compressed_size > PAGE_SIZE' case easily in ZRAM, but when we
+	 * receive -ERRNO from the compressing backend we can't help it
+	 * anymore. To make `842' happy we need to tell the exact size of
+	 * the dst buffer, zram_drv will take care of the fact that
+	 * compressed buffer is too big.
+	 */
+	*dst_len = PAGE_SIZE * 2;
+
+	return crypto_comp_compress(zstrm->tfm,
+			src, PAGE_SIZE,
+			zstrm->buffer, dst_len);
+}
+
+int zcomp_decompress(struct zcomp_strm *zstrm,
+		const void *src, unsigned int src_len, void *dst)
+{
+	unsigned int dst_len = PAGE_SIZE;
+
+	return crypto_comp_decompress(zstrm->tfm,
+			src, src_len,
+			dst, &dst_len);
+}
+
+int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node)
+{
+	struct zcomp *comp = hlist_entry(node, struct zcomp, node);
+	struct zcomp_strm *zstrm;
+	int ret;
+
+	zstrm = per_cpu_ptr(comp->stream, cpu);
+	local_lock_init(&zstrm->lock);
+
+	ret = zcomp_strm_init(zstrm, comp);
+	if (ret)
+		pr_err("Can't allocate a compression stream\n");
+	return ret;
+}
+
+int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node)
+{
+	struct zcomp *comp = hlist_entry(node, struct zcomp, node);
+	struct zcomp_strm *zstrm;
+
+	zstrm = per_cpu_ptr(comp->stream, cpu);
+	zcomp_strm_free(zstrm);
+	return 0;
+}
+
+static int zcomp_init(struct zcomp *comp)
+{
+	int ret;
+
+	comp->stream = alloc_percpu(struct zcomp_strm);
+	if (!comp->stream)
+		return -ENOMEM;
+
+	ret = cpuhp_state_add_instance(CPUHP_ZCOMP_PREPARE, &comp->node);
+	if (ret < 0)
+		goto cleanup;
+	return 0;
+
+cleanup:
+	free_percpu(comp->stream);
+	return ret;
+}
+
+void zcomp_destroy(struct zcomp *comp)
+{
+	cpuhp_state_remove_instance(CPUHP_ZCOMP_PREPARE, &comp->node);
+	free_percpu(comp->stream);
+	kfree(comp);
+}
+
+/*
+ * search available compressors for requested algorithm.
+ * allocate new zcomp and initialize it. return compressing
+ * backend pointer or ERR_PTR if things went bad. ERR_PTR(-EINVAL)
+ * if requested algorithm is not supported, ERR_PTR(-ENOMEM) in
+ * case of allocation error, or any other error potentially
+ * returned by zcomp_init().
+ */
+struct zcomp *zcomp_create(const char *compress)
+{
+	struct zcomp *comp;
+	int error;
+
+	/*
+	 * Crypto API will execute /sbin/modprobe if the compression module
+	 * 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))
+		return ERR_PTR(-EINVAL);
+
+	comp = kzalloc(sizeof(struct zcomp), GFP_KERNEL);
+	if (!comp)
+		return ERR_PTR(-ENOMEM);
+
+	comp->name = compress;
+	error = zcomp_init(comp);
+	if (error) {
+		kfree(comp);
+		return ERR_PTR(error);
+	}
+	return comp;
+}
diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
new file mode 100644
index 000000000..40f6420f4
--- /dev/null
+++ b/drivers/block/zram/zcomp.h
@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2014 Sergey Senozhatsky.
+ */
+
+#ifndef _ZCOMP_H_
+#define _ZCOMP_H_
+#include <linux/local_lock.h>
+
+struct zcomp_strm {
+	/* The members ->buffer and ->tfm are protected by ->lock. */
+	local_lock_t lock;
+	/* compression/decompression buffer */
+	void *buffer;
+	struct crypto_comp *tfm;
+};
+
+/* dynamic per-device compression frontend */
+struct zcomp {
+	struct zcomp_strm __percpu *stream;
+	const char *name;
+	struct hlist_node node;
+};
+
+int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node);
+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);
+void zcomp_destroy(struct zcomp *comp);
+
+struct zcomp_strm *zcomp_stream_get(struct zcomp *comp);
+void zcomp_stream_put(struct zcomp *comp);
+
+int zcomp_compress(struct zcomp_strm *zstrm,
+		const void *src, unsigned int *dst_len);
+
+int zcomp_decompress(struct zcomp_strm *zstrm,
+		const void *src, unsigned int src_len, void *dst);
+
+bool zcomp_set_max_streams(struct zcomp *comp, int num_strm);
+#endif /* _ZCOMP_H_ */
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
new file mode 100644
index 000000000..0636df6b6
--- /dev/null
+++ b/drivers/block/zram/zram_drv.c
@@ -0,0 +1,2156 @@
+/*
+ * Compressed RAM block device
+ *
+ * Copyright (C) 2008, 2009, 2010  Nitin Gupta
+ *               2012, 2013 Minchan Kim
+ *
+ * This code is released using a dual license strategy: BSD/GPL
+ * You can choose the licence that better fits your requirements.
+ *
+ * Released under the terms of 3-clause BSD License
+ * Released under the terms of GNU General Public License Version 2.0
+ *
+ */
+
+#define KMSG_COMPONENT "zram"
+#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/bio.h>
+#include <linux/bitops.h>
+#include <linux/blkdev.h>
+#include <linux/buffer_head.h>
+#include <linux/device.h>
+#include <linux/genhd.h>
+#include <linux/highmem.h>
+#include <linux/slab.h>
+#include <linux/backing-dev.h>
+#include <linux/string.h>
+#include <linux/vmalloc.h>
+#include <linux/err.h>
+#include <linux/idr.h>
+#include <linux/sysfs.h>
+#include <linux/debugfs.h>
+#include <linux/cpuhotplug.h>
+#include <linux/part_stat.h>
+
+#include "zram_drv.h"
+
+static DEFINE_IDR(zram_index_idr);
+/* idr index must be protected */
+static DEFINE_MUTEX(zram_index_mutex);
+
+static int zram_major;
+static const char *default_compressor = "lzo-rle";
+
+/* Module params (documentation at end) */
+static unsigned int num_devices = 1;
+/*
+ * Pages that compress to sizes equals or greater than this are stored
+ * uncompressed in memory.
+ */
+static size_t huge_class_size;
+
+static const struct block_device_operations zram_devops;
+static const struct block_device_operations zram_wb_devops;
+
+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);
+
+
+static int zram_slot_trylock(struct zram *zram, u32 index)
+{
+	return bit_spin_trylock(ZRAM_LOCK, &zram->table[index].flags);
+}
+
+static void zram_slot_lock(struct zram *zram, u32 index)
+{
+	bit_spin_lock(ZRAM_LOCK, &zram->table[index].flags);
+}
+
+static void zram_slot_unlock(struct zram *zram, u32 index)
+{
+	bit_spin_unlock(ZRAM_LOCK, &zram->table[index].flags);
+}
+
+static inline bool init_done(struct zram *zram)
+{
+	return zram->disksize;
+}
+
+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)
+{
+	return zram->table[index].handle;
+}
+
+static void zram_set_handle(struct zram *zram, u32 index, unsigned long handle)
+{
+	zram->table[index].handle = handle;
+}
+
+/* flag operations require table entry bit_spin_lock() being held */
+static bool zram_test_flag(struct zram *zram, u32 index,
+			enum zram_pageflags flag)
+{
+	return zram->table[index].flags & BIT(flag);
+}
+
+static void zram_set_flag(struct zram *zram, u32 index,
+			enum zram_pageflags flag)
+{
+	zram->table[index].flags |= BIT(flag);
+}
+
+static void zram_clear_flag(struct zram *zram, u32 index,
+			enum zram_pageflags flag)
+{
+	zram->table[index].flags &= ~BIT(flag);
+}
+
+static inline void zram_set_element(struct zram *zram, u32 index,
+			unsigned long element)
+{
+	zram->table[index].element = element;
+}
+
+static unsigned long zram_get_element(struct zram *zram, u32 index)
+{
+	return zram->table[index].element;
+}
+
+static size_t zram_get_obj_size(struct zram *zram, u32 index)
+{
+	return zram->table[index].flags & (BIT(ZRAM_FLAG_SHIFT) - 1);
+}
+
+static void zram_set_obj_size(struct zram *zram,
+					u32 index, size_t size)
+{
+	unsigned long flags = zram->table[index].flags >> ZRAM_FLAG_SHIFT;
+
+	zram->table[index].flags = (flags << ZRAM_FLAG_SHIFT) | size;
+}
+
+static inline bool zram_allocated(struct zram *zram, u32 index)
+{
+	return zram_get_obj_size(zram, index) ||
+			zram_test_flag(zram, index, ZRAM_SAME) ||
+			zram_test_flag(zram, index, ZRAM_WB);
+}
+
+#if PAGE_SIZE != 4096
+static inline bool is_partial_io(struct bio_vec *bvec)
+{
+	return bvec->bv_len != PAGE_SIZE;
+}
+#else
+static inline bool is_partial_io(struct bio_vec *bvec)
+{
+	return false;
+}
+#endif
+
+/*
+ * Check if request is within bounds and aligned on zram logical blocks.
+ */
+static inline bool valid_io_request(struct zram *zram,
+		sector_t start, unsigned int size)
+{
+	u64 end, bound;
+
+	/* unaligned request */
+	if (unlikely(start & (ZRAM_SECTOR_PER_LOGICAL_BLOCK - 1)))
+		return false;
+	if (unlikely(size & (ZRAM_LOGICAL_BLOCK_SIZE - 1)))
+		return false;
+
+	end = start + (size >> SECTOR_SHIFT);
+	bound = zram->disksize >> SECTOR_SHIFT;
+	/* out of range range */
+	if (unlikely(start >= bound || end > bound || start > end))
+		return false;
+
+	/* I/O request is valid */
+	return true;
+}
+
+static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
+{
+	*index  += (*offset + bvec->bv_len) / PAGE_SIZE;
+	*offset = (*offset + bvec->bv_len) % PAGE_SIZE;
+}
+
+static inline void update_used_max(struct zram *zram,
+					const unsigned long pages)
+{
+	unsigned long old_max, cur_max;
+
+	old_max = atomic_long_read(&zram->stats.max_used_pages);
+
+	do {
+		cur_max = old_max;
+		if (pages > cur_max)
+			old_max = atomic_long_cmpxchg(
+				&zram->stats.max_used_pages, cur_max, pages);
+	} while (old_max != cur_max);
+}
+
+static inline void zram_fill_page(void *ptr, unsigned long len,
+					unsigned long value)
+{
+	WARN_ON_ONCE(!IS_ALIGNED(len, sizeof(unsigned long)));
+	memset_l(ptr, value, len / sizeof(unsigned long));
+}
+
+static bool page_same_filled(void *ptr, unsigned long *element)
+{
+	unsigned long *page;
+	unsigned long val;
+	unsigned int pos, last_pos = PAGE_SIZE / sizeof(*page) - 1;
+
+	page = (unsigned long *)ptr;
+	val = page[0];
+
+	if (val != page[last_pos])
+		return false;
+
+	for (pos = 1; pos < last_pos; pos++) {
+		if (val != page[pos])
+			return false;
+	}
+
+	*element = val;
+
+	return true;
+}
+
+static ssize_t initstate_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	u32 val;
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	val = init_done(zram);
+	up_read(&zram->init_lock);
+
+	return scnprintf(buf, PAGE_SIZE, "%u\n", val);
+}
+
+static ssize_t disksize_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+
+	return scnprintf(buf, PAGE_SIZE, "%llu\n", zram->disksize);
+}
+
+static ssize_t mem_limit_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	u64 limit;
+	char *tmp;
+	struct zram *zram = dev_to_zram(dev);
+
+	limit = memparse(buf, &tmp);
+	if (buf == tmp) /* no chars parsed, invalid input */
+		return -EINVAL;
+
+	down_write(&zram->init_lock);
+	zram->limit_pages = PAGE_ALIGN(limit) >> PAGE_SHIFT;
+	up_write(&zram->init_lock);
+
+	return len;
+}
+
+static ssize_t mem_used_max_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	int err;
+	unsigned long val;
+	struct zram *zram = dev_to_zram(dev);
+
+	err = kstrtoul(buf, 10, &val);
+	if (err || val != 0)
+		return -EINVAL;
+
+	down_read(&zram->init_lock);
+	if (init_done(zram)) {
+		atomic_long_set(&zram->stats.max_used_pages,
+				zs_get_total_pages(zram->mem_pool));
+	}
+	up_read(&zram->init_lock);
+
+	return len;
+}
+
+static ssize_t idle_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
+	int index;
+
+	if (!sysfs_streq(buf, "all"))
+		return -EINVAL;
+
+	down_read(&zram->init_lock);
+	if (!init_done(zram)) {
+		up_read(&zram->init_lock);
+		return -EINVAL;
+	}
+
+	for (index = 0; index < nr_pages; index++) {
+		/*
+		 * Do not mark ZRAM_UNDER_WB slot as ZRAM_IDLE to close race.
+		 * See the comment in writeback_store.
+		 */
+		zram_slot_lock(zram, index);
+		if (zram_allocated(zram, index) &&
+				!zram_test_flag(zram, index, ZRAM_UNDER_WB))
+			zram_set_flag(zram, index, ZRAM_IDLE);
+		zram_slot_unlock(zram, index);
+	}
+
+	up_read(&zram->init_lock);
+
+	return len;
+}
+
+#ifdef CONFIG_ZRAM_WRITEBACK
+static ssize_t writeback_limit_enable_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	u64 val;
+	ssize_t ret = -EINVAL;
+
+	if (kstrtoull(buf, 10, &val))
+		return ret;
+
+	down_read(&zram->init_lock);
+	spin_lock(&zram->wb_limit_lock);
+	zram->wb_limit_enable = val;
+	spin_unlock(&zram->wb_limit_lock);
+	up_read(&zram->init_lock);
+	ret = len;
+
+	return ret;
+}
+
+static ssize_t writeback_limit_enable_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	bool val;
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	spin_lock(&zram->wb_limit_lock);
+	val = zram->wb_limit_enable;
+	spin_unlock(&zram->wb_limit_lock);
+	up_read(&zram->init_lock);
+
+	return scnprintf(buf, PAGE_SIZE, "%d\n", val);
+}
+
+static ssize_t writeback_limit_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	u64 val;
+	ssize_t ret = -EINVAL;
+
+	if (kstrtoull(buf, 10, &val))
+		return ret;
+
+	down_read(&zram->init_lock);
+	spin_lock(&zram->wb_limit_lock);
+	zram->bd_wb_limit = val;
+	spin_unlock(&zram->wb_limit_lock);
+	up_read(&zram->init_lock);
+	ret = len;
+
+	return ret;
+}
+
+static ssize_t writeback_limit_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	u64 val;
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	spin_lock(&zram->wb_limit_lock);
+	val = zram->bd_wb_limit;
+	spin_unlock(&zram->wb_limit_lock);
+	up_read(&zram->init_lock);
+
+	return scnprintf(buf, PAGE_SIZE, "%llu\n", val);
+}
+
+static void reset_bdev(struct zram *zram)
+{
+	struct block_device *bdev;
+
+	if (!zram->backing_dev)
+		return;
+
+	bdev = zram->bdev;
+	if (zram->old_block_size)
+		set_blocksize(bdev, zram->old_block_size);
+	blkdev_put(bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
+	/* hope filp_close flush all of IO */
+	filp_close(zram->backing_dev, NULL);
+	zram->backing_dev = NULL;
+	zram->old_block_size = 0;
+	zram->bdev = NULL;
+	zram->disk->fops = &zram_devops;
+	kvfree(zram->bitmap);
+	zram->bitmap = NULL;
+}
+
+static ssize_t backing_dev_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct file *file;
+	struct zram *zram = dev_to_zram(dev);
+	char *p;
+	ssize_t ret;
+
+	down_read(&zram->init_lock);
+	file = zram->backing_dev;
+	if (!file) {
+		memcpy(buf, "none\n", 5);
+		up_read(&zram->init_lock);
+		return 5;
+	}
+
+	p = file_path(file, buf, PAGE_SIZE - 1);
+	if (IS_ERR(p)) {
+		ret = PTR_ERR(p);
+		goto out;
+	}
+
+	ret = strlen(p);
+	memmove(buf, p, ret);
+	buf[ret++] = '\n';
+out:
+	up_read(&zram->init_lock);
+	return ret;
+}
+
+static ssize_t backing_dev_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	char *file_name;
+	size_t sz;
+	struct file *backing_dev = NULL;
+	struct inode *inode;
+	struct address_space *mapping;
+	unsigned int bitmap_sz, old_block_size = 0;
+	unsigned long nr_pages, *bitmap = NULL;
+	struct block_device *bdev = NULL;
+	int err;
+	struct zram *zram = dev_to_zram(dev);
+
+	file_name = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!file_name)
+		return -ENOMEM;
+
+	down_write(&zram->init_lock);
+	if (init_done(zram)) {
+		pr_info("Can't setup backing device for initialized device\n");
+		err = -EBUSY;
+		goto out;
+	}
+
+	strlcpy(file_name, buf, PATH_MAX);
+	/* ignore trailing newline */
+	sz = strlen(file_name);
+	if (sz > 0 && file_name[sz - 1] == '\n')
+		file_name[sz - 1] = 0x00;
+
+	backing_dev = filp_open(file_name, O_RDWR|O_LARGEFILE, 0);
+	if (IS_ERR(backing_dev)) {
+		err = PTR_ERR(backing_dev);
+		backing_dev = NULL;
+		goto out;
+	}
+
+	mapping = backing_dev->f_mapping;
+	inode = mapping->host;
+
+	/* Support only block device in this moment */
+	if (!S_ISBLK(inode->i_mode)) {
+		err = -ENOTBLK;
+		goto out;
+	}
+
+	bdev = blkdev_get_by_dev(inode->i_rdev,
+			FMODE_READ | FMODE_WRITE | FMODE_EXCL, zram);
+	if (IS_ERR(bdev)) {
+		err = PTR_ERR(bdev);
+		bdev = NULL;
+		goto out;
+	}
+
+	nr_pages = i_size_read(inode) >> PAGE_SHIFT;
+	bitmap_sz = BITS_TO_LONGS(nr_pages) * sizeof(long);
+	bitmap = kvzalloc(bitmap_sz, GFP_KERNEL);
+	if (!bitmap) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	old_block_size = block_size(bdev);
+	err = set_blocksize(bdev, PAGE_SIZE);
+	if (err)
+		goto out;
+
+	reset_bdev(zram);
+
+	zram->old_block_size = old_block_size;
+	zram->bdev = bdev;
+	zram->backing_dev = backing_dev;
+	zram->bitmap = bitmap;
+	zram->nr_pages = nr_pages;
+	/*
+	 * With writeback feature, zram does asynchronous IO so it's no longer
+	 * synchronous device so let's remove synchronous io flag. Othewise,
+	 * upper layer(e.g., swap) could wait IO completion rather than
+	 * (submit and return), which will cause system sluggish.
+	 * Furthermore, when the IO function returns(e.g., swap_readpage),
+	 * upper layer expects IO was done so it could deallocate the page
+	 * freely but in fact, IO is going on so finally could cause
+	 * use-after-free when the IO is really done.
+	 */
+	zram->disk->fops = &zram_wb_devops;
+	up_write(&zram->init_lock);
+
+	pr_info("setup backing device %s\n", file_name);
+	kfree(file_name);
+
+	return len;
+out:
+	if (bitmap)
+		kvfree(bitmap);
+
+	if (bdev)
+		blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
+
+	if (backing_dev)
+		filp_close(backing_dev, NULL);
+
+	up_write(&zram->init_lock);
+
+	kfree(file_name);
+
+	return err;
+}
+
+static unsigned long alloc_block_bdev(struct zram *zram)
+{
+	unsigned long blk_idx = 1;
+retry:
+	/* skip 0 bit to confuse zram.handle = 0 */
+	blk_idx = find_next_zero_bit(zram->bitmap, zram->nr_pages, blk_idx);
+	if (blk_idx == zram->nr_pages)
+		return 0;
+
+	if (test_and_set_bit(blk_idx, zram->bitmap))
+		goto retry;
+
+	atomic64_inc(&zram->stats.bd_count);
+	return blk_idx;
+}
+
+static void free_block_bdev(struct zram *zram, unsigned long blk_idx)
+{
+	int was_set;
+
+	was_set = test_and_clear_bit(blk_idx, zram->bitmap);
+	WARN_ON_ONCE(!was_set);
+	atomic64_dec(&zram->stats.bd_count);
+}
+
+static void zram_page_end_io(struct bio *bio)
+{
+	struct page *page = bio_first_page_all(bio);
+
+	page_endio(page, op_is_write(bio_op(bio)),
+			blk_status_to_errno(bio->bi_status));
+	bio_put(bio);
+}
+
+/*
+ * Returns 1 if the submission is successful.
+ */
+static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
+			unsigned long entry, struct bio *parent)
+{
+	struct bio *bio;
+
+	bio = bio_alloc(GFP_ATOMIC, 1);
+	if (!bio)
+		return -ENOMEM;
+
+	bio->bi_iter.bi_sector = entry * (PAGE_SIZE >> 9);
+	bio_set_dev(bio, zram->bdev);
+	if (!bio_add_page(bio, bvec->bv_page, bvec->bv_len, bvec->bv_offset)) {
+		bio_put(bio);
+		return -EIO;
+	}
+
+	if (!parent) {
+		bio->bi_opf = REQ_OP_READ;
+		bio->bi_end_io = zram_page_end_io;
+	} else {
+		bio->bi_opf = parent->bi_opf;
+		bio_chain(bio, parent);
+	}
+
+	submit_bio(bio);
+	return 1;
+}
+
+#define HUGE_WRITEBACK 1
+#define IDLE_WRITEBACK 2
+
+static ssize_t writeback_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
+	unsigned long index;
+	struct bio bio;
+	struct bio_vec bio_vec;
+	struct page *page;
+	ssize_t ret = len;
+	int mode, err;
+	unsigned long blk_idx = 0;
+
+	if (sysfs_streq(buf, "idle"))
+		mode = IDLE_WRITEBACK;
+	else if (sysfs_streq(buf, "huge"))
+		mode = HUGE_WRITEBACK;
+	else
+		return -EINVAL;
+
+	down_read(&zram->init_lock);
+	if (!init_done(zram)) {
+		ret = -EINVAL;
+		goto release_init_lock;
+	}
+
+	if (!zram->backing_dev) {
+		ret = -ENODEV;
+		goto release_init_lock;
+	}
+
+	page = alloc_page(GFP_KERNEL);
+	if (!page) {
+		ret = -ENOMEM;
+		goto release_init_lock;
+	}
+
+	for (index = 0; index < nr_pages; index++) {
+		struct bio_vec bvec;
+
+		bvec.bv_page = page;
+		bvec.bv_len = PAGE_SIZE;
+		bvec.bv_offset = 0;
+
+		spin_lock(&zram->wb_limit_lock);
+		if (zram->wb_limit_enable && !zram->bd_wb_limit) {
+			spin_unlock(&zram->wb_limit_lock);
+			ret = -EIO;
+			break;
+		}
+		spin_unlock(&zram->wb_limit_lock);
+
+		if (!blk_idx) {
+			blk_idx = alloc_block_bdev(zram);
+			if (!blk_idx) {
+				ret = -ENOSPC;
+				break;
+			}
+		}
+
+		zram_slot_lock(zram, index);
+		if (!zram_allocated(zram, index))
+			goto next;
+
+		if (zram_test_flag(zram, index, ZRAM_WB) ||
+				zram_test_flag(zram, index, ZRAM_SAME) ||
+				zram_test_flag(zram, index, ZRAM_UNDER_WB))
+			goto next;
+
+		if (mode == IDLE_WRITEBACK &&
+			  !zram_test_flag(zram, index, ZRAM_IDLE))
+			goto next;
+		if (mode == HUGE_WRITEBACK &&
+			  !zram_test_flag(zram, index, ZRAM_HUGE))
+			goto next;
+		/*
+		 * Clearing ZRAM_UNDER_WB is duty of caller.
+		 * IOW, zram_free_page never clear it.
+		 */
+		zram_set_flag(zram, index, ZRAM_UNDER_WB);
+		/* Need for hugepage writeback racing */
+		zram_set_flag(zram, index, ZRAM_IDLE);
+		zram_slot_unlock(zram, index);
+		if (zram_bvec_read(zram, &bvec, index, 0, NULL)) {
+			zram_slot_lock(zram, index);
+			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
+			zram_clear_flag(zram, index, ZRAM_IDLE);
+			zram_slot_unlock(zram, index);
+			continue;
+		}
+
+		bio_init(&bio, &bio_vec, 1);
+		bio_set_dev(&bio, zram->bdev);
+		bio.bi_iter.bi_sector = blk_idx * (PAGE_SIZE >> 9);
+		bio.bi_opf = REQ_OP_WRITE | REQ_SYNC;
+
+		bio_add_page(&bio, bvec.bv_page, bvec.bv_len,
+				bvec.bv_offset);
+		/*
+		 * XXX: A single page IO would be inefficient for write
+		 * but it would be not bad as starter.
+		 */
+		err = submit_bio_wait(&bio);
+		if (err) {
+			zram_slot_lock(zram, index);
+			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
+			zram_clear_flag(zram, index, ZRAM_IDLE);
+			zram_slot_unlock(zram, index);
+			/*
+			 * Return last IO error unless every IO were
+			 * not suceeded.
+			 */
+			ret = err;
+			continue;
+		}
+
+		atomic64_inc(&zram->stats.bd_writes);
+		/*
+		 * We released zram_slot_lock so need to check if the slot was
+		 * changed. If there is freeing for the slot, we can catch it
+		 * easily by zram_allocated.
+		 * A subtle case is the slot is freed/reallocated/marked as
+		 * ZRAM_IDLE again. To close the race, idle_store doesn't
+		 * mark ZRAM_IDLE once it found the slot was ZRAM_UNDER_WB.
+		 * Thus, we could close the race by checking ZRAM_IDLE bit.
+		 */
+		zram_slot_lock(zram, index);
+		if (!zram_allocated(zram, index) ||
+			  !zram_test_flag(zram, index, ZRAM_IDLE)) {
+			zram_clear_flag(zram, index, ZRAM_UNDER_WB);
+			zram_clear_flag(zram, index, ZRAM_IDLE);
+			goto next;
+		}
+
+		zram_free_page(zram, index);
+		zram_clear_flag(zram, index, ZRAM_UNDER_WB);
+		zram_set_flag(zram, index, ZRAM_WB);
+		zram_set_element(zram, index, blk_idx);
+		blk_idx = 0;
+		atomic64_inc(&zram->stats.pages_stored);
+		spin_lock(&zram->wb_limit_lock);
+		if (zram->wb_limit_enable && zram->bd_wb_limit > 0)
+			zram->bd_wb_limit -=  1UL << (PAGE_SHIFT - 12);
+		spin_unlock(&zram->wb_limit_lock);
+next:
+		zram_slot_unlock(zram, index);
+	}
+
+	if (blk_idx)
+		free_block_bdev(zram, blk_idx);
+	__free_page(page);
+release_init_lock:
+	up_read(&zram->init_lock);
+
+	return ret;
+}
+
+struct zram_work {
+	struct work_struct work;
+	struct zram *zram;
+	unsigned long entry;
+	struct bio *bio;
+	struct bio_vec bvec;
+};
+
+#if PAGE_SIZE != 4096
+static void zram_sync_read(struct work_struct *work)
+{
+	struct zram_work *zw = container_of(work, struct zram_work, work);
+	struct zram *zram = zw->zram;
+	unsigned long entry = zw->entry;
+	struct bio *bio = zw->bio;
+
+	read_from_bdev_async(zram, &zw->bvec, entry, bio);
+}
+
+/*
+ * Block layer want one ->submit_bio to be active at a time, so if we use
+ * chained IO with parent IO in same context, it's a deadlock. To avoid that,
+ * use a worker thread context.
+ */
+static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
+				unsigned long entry, struct bio *bio)
+{
+	struct zram_work work;
+
+	work.bvec = *bvec;
+	work.zram = zram;
+	work.entry = entry;
+	work.bio = bio;
+
+	INIT_WORK_ONSTACK(&work.work, zram_sync_read);
+	queue_work(system_unbound_wq, &work.work);
+	flush_work(&work.work);
+	destroy_work_on_stack(&work.work);
+
+	return 1;
+}
+#else
+static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
+				unsigned long entry, struct bio *bio)
+{
+	WARN_ON(1);
+	return -EIO;
+}
+#endif
+
+static int read_from_bdev(struct zram *zram, struct bio_vec *bvec,
+			unsigned long entry, struct bio *parent, bool sync)
+{
+	atomic64_inc(&zram->stats.bd_reads);
+	if (sync)
+		return read_from_bdev_sync(zram, bvec, entry, parent);
+	else
+		return read_from_bdev_async(zram, bvec, entry, parent);
+}
+#else
+static inline void reset_bdev(struct zram *zram) {};
+static int read_from_bdev(struct zram *zram, struct bio_vec *bvec,
+			unsigned long entry, struct bio *parent, bool sync)
+{
+	return -EIO;
+}
+
+static void free_block_bdev(struct zram *zram, unsigned long blk_idx) {};
+#endif
+
+#ifdef CONFIG_ZRAM_MEMORY_TRACKING
+
+static struct dentry *zram_debugfs_root;
+
+static void zram_debugfs_create(void)
+{
+	zram_debugfs_root = debugfs_create_dir("zram", NULL);
+}
+
+static void zram_debugfs_destroy(void)
+{
+	debugfs_remove_recursive(zram_debugfs_root);
+}
+
+static void zram_accessed(struct zram *zram, u32 index)
+{
+	zram_clear_flag(zram, index, ZRAM_IDLE);
+	zram->table[index].ac_time = ktime_get_boottime();
+}
+
+static ssize_t read_block_state(struct file *file, char __user *buf,
+				size_t count, loff_t *ppos)
+{
+	char *kbuf;
+	ssize_t index, written = 0;
+	struct zram *zram = file->private_data;
+	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
+	struct timespec64 ts;
+
+	kbuf = kvmalloc(count, GFP_KERNEL);
+	if (!kbuf)
+		return -ENOMEM;
+
+	down_read(&zram->init_lock);
+	if (!init_done(zram)) {
+		up_read(&zram->init_lock);
+		kvfree(kbuf);
+		return -EINVAL;
+	}
+
+	for (index = *ppos; index < nr_pages; index++) {
+		int copied;
+
+		zram_slot_lock(zram, index);
+		if (!zram_allocated(zram, index))
+			goto next;
+
+		ts = ktime_to_timespec64(zram->table[index].ac_time);
+		copied = snprintf(kbuf + written, count,
+			"%12zd %12lld.%06lu %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' : '.');
+
+		if (count <= copied) {
+			zram_slot_unlock(zram, index);
+			break;
+		}
+		written += copied;
+		count -= copied;
+next:
+		zram_slot_unlock(zram, index);
+		*ppos += 1;
+	}
+
+	up_read(&zram->init_lock);
+	if (copy_to_user(buf, kbuf, written))
+		written = -EFAULT;
+	kvfree(kbuf);
+
+	return written;
+}
+
+static const struct file_operations proc_zram_block_state_op = {
+	.open = simple_open,
+	.read = read_block_state,
+	.llseek = default_llseek,
+};
+
+static void zram_debugfs_register(struct zram *zram)
+{
+	if (!zram_debugfs_root)
+		return;
+
+	zram->debugfs_dir = debugfs_create_dir(zram->disk->disk_name,
+						zram_debugfs_root);
+	debugfs_create_file("block_state", 0400, zram->debugfs_dir,
+				zram, &proc_zram_block_state_op);
+}
+
+static void zram_debugfs_unregister(struct zram *zram)
+{
+	debugfs_remove_recursive(zram->debugfs_dir);
+}
+#else
+static void zram_debugfs_create(void) {};
+static void zram_debugfs_destroy(void) {};
+static void zram_accessed(struct zram *zram, u32 index)
+{
+	zram_clear_flag(zram, index, ZRAM_IDLE);
+};
+static void zram_debugfs_register(struct zram *zram) {};
+static void zram_debugfs_unregister(struct zram *zram) {};
+#endif
+
+/*
+ * We switched to per-cpu streams and this attr is not needed anymore.
+ * However, we will keep it around for some time, because:
+ * a) we may revert per-cpu streams in the future
+ * b) it's visible to user space and we need to follow our 2 years
+ *    retirement rule; but we already have a number of 'soon to be
+ *    altered' attrs, so max_comp_streams need to wait for the next
+ *    layoff cycle.
+ */
+static ssize_t max_comp_streams_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	return scnprintf(buf, PAGE_SIZE, "%d\n", num_online_cpus());
+}
+
+static ssize_t max_comp_streams_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	return len;
+}
+
+static ssize_t comp_algorithm_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	size_t sz;
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	sz = zcomp_available_show(zram->compressor, 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)
+{
+	struct zram *zram = dev_to_zram(dev);
+	char compressor[ARRAY_SIZE(zram->compressor)];
+	size_t sz;
+
+	strlcpy(compressor, buf, sizeof(compressor));
+	/* ignore trailing newline */
+	sz = strlen(compressor);
+	if (sz > 0 && compressor[sz - 1] == '\n')
+		compressor[sz - 1] = 0x00;
+
+	if (!zcomp_available_algorithm(compressor))
+		return -EINVAL;
+
+	down_write(&zram->init_lock);
+	if (init_done(zram)) {
+		up_write(&zram->init_lock);
+		pr_info("Can't change algorithm for initialized device\n");
+		return -EBUSY;
+	}
+
+	strcpy(zram->compressor, compressor);
+	up_write(&zram->init_lock);
+	return len;
+}
+
+static ssize_t compact_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	if (!init_done(zram)) {
+		up_read(&zram->init_lock);
+		return -EINVAL;
+	}
+
+	zs_compact(zram->mem_pool);
+	up_read(&zram->init_lock);
+
+	return len;
+}
+
+static ssize_t io_stat_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+	ssize_t ret;
+
+	down_read(&zram->init_lock);
+	ret = scnprintf(buf, PAGE_SIZE,
+			"%8llu %8llu %8llu %8llu\n",
+			(u64)atomic64_read(&zram->stats.failed_reads),
+			(u64)atomic64_read(&zram->stats.failed_writes),
+			(u64)atomic64_read(&zram->stats.invalid_io),
+			(u64)atomic64_read(&zram->stats.notify_free));
+	up_read(&zram->init_lock);
+
+	return ret;
+}
+
+static ssize_t mm_stat_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+	struct zs_pool_stats pool_stats;
+	u64 orig_size, mem_used = 0;
+	long max_used;
+	ssize_t ret;
+
+	memset(&pool_stats, 0x00, sizeof(struct zs_pool_stats));
+
+	down_read(&zram->init_lock);
+	if (init_done(zram)) {
+		mem_used = zs_get_total_pages(zram->mem_pool);
+		zs_pool_stats(zram->mem_pool, &pool_stats);
+	}
+
+	orig_size = atomic64_read(&zram->stats.pages_stored);
+	max_used = atomic_long_read(&zram->stats.max_used_pages);
+
+	ret = scnprintf(buf, PAGE_SIZE,
+			"%8llu %8llu %8llu %8lu %8ld %8llu %8lu %8llu\n",
+			orig_size << PAGE_SHIFT,
+			(u64)atomic64_read(&zram->stats.compr_data_size),
+			mem_used << PAGE_SHIFT,
+			zram->limit_pages << PAGE_SHIFT,
+			max_used << PAGE_SHIFT,
+			(u64)atomic64_read(&zram->stats.same_pages),
+			atomic_long_read(&pool_stats.pages_compacted),
+			(u64)atomic64_read(&zram->stats.huge_pages));
+	up_read(&zram->init_lock);
+
+	return ret;
+}
+
+#ifdef CONFIG_ZRAM_WRITEBACK
+#define FOUR_K(x) ((x) * (1 << (PAGE_SHIFT - 12)))
+static ssize_t bd_stat_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+	ssize_t ret;
+
+	down_read(&zram->init_lock);
+	ret = scnprintf(buf, PAGE_SIZE,
+		"%8llu %8llu %8llu\n",
+			FOUR_K((u64)atomic64_read(&zram->stats.bd_count)),
+			FOUR_K((u64)atomic64_read(&zram->stats.bd_reads)),
+			FOUR_K((u64)atomic64_read(&zram->stats.bd_writes)));
+	up_read(&zram->init_lock);
+
+	return ret;
+}
+#endif
+
+static ssize_t debug_stat_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	int version = 1;
+	struct zram *zram = dev_to_zram(dev);
+	ssize_t ret;
+
+	down_read(&zram->init_lock);
+	ret = scnprintf(buf, PAGE_SIZE,
+			"version: %d\n%8llu %8llu\n",
+			version,
+			(u64)atomic64_read(&zram->stats.writestall),
+			(u64)atomic64_read(&zram->stats.miss_free));
+	up_read(&zram->init_lock);
+
+	return ret;
+}
+
+static DEVICE_ATTR_RO(io_stat);
+static DEVICE_ATTR_RO(mm_stat);
+#ifdef CONFIG_ZRAM_WRITEBACK
+static DEVICE_ATTR_RO(bd_stat);
+#endif
+static DEVICE_ATTR_RO(debug_stat);
+
+static void zram_meta_free(struct zram *zram, u64 disksize)
+{
+	size_t num_pages = disksize >> PAGE_SHIFT;
+	size_t index;
+
+	/* Free all pages that are still in this zram device */
+	for (index = 0; index < num_pages; index++)
+		zram_free_page(zram, index);
+
+	zs_destroy_pool(zram->mem_pool);
+	vfree(zram->table);
+}
+
+static bool zram_meta_alloc(struct zram *zram, u64 disksize)
+{
+	size_t num_pages;
+
+	num_pages = disksize >> PAGE_SHIFT;
+	zram->table = vzalloc(array_size(num_pages, sizeof(*zram->table)));
+	if (!zram->table)
+		return false;
+
+	zram->mem_pool = zs_create_pool(zram->disk->disk_name);
+	if (!zram->mem_pool) {
+		vfree(zram->table);
+		return false;
+	}
+
+	if (!huge_class_size)
+		huge_class_size = zs_huge_class_size(zram->mem_pool);
+	return true;
+}
+
+/*
+ * To protect concurrent access to the same index entry,
+ * caller should hold this table index entry's bit_spinlock to
+ * indicate this index entry is accessing.
+ */
+static void zram_free_page(struct zram *zram, size_t index)
+{
+	unsigned long handle;
+
+#ifdef CONFIG_ZRAM_MEMORY_TRACKING
+	zram->table[index].ac_time = 0;
+#endif
+	if (zram_test_flag(zram, index, ZRAM_IDLE))
+		zram_clear_flag(zram, index, ZRAM_IDLE);
+
+	if (zram_test_flag(zram, index, ZRAM_HUGE)) {
+		zram_clear_flag(zram, index, ZRAM_HUGE);
+		atomic64_dec(&zram->stats.huge_pages);
+	}
+
+	if (zram_test_flag(zram, index, ZRAM_WB)) {
+		zram_clear_flag(zram, index, ZRAM_WB);
+		free_block_bdev(zram, zram_get_element(zram, index));
+		goto out;
+	}
+
+	/*
+	 * No memory is allocated for same element filled pages.
+	 * Simply clear same page flag.
+	 */
+	if (zram_test_flag(zram, index, ZRAM_SAME)) {
+		zram_clear_flag(zram, index, ZRAM_SAME);
+		atomic64_dec(&zram->stats.same_pages);
+		goto out;
+	}
+
+	handle = zram_get_handle(zram, index);
+	if (!handle)
+		return;
+
+	zs_free(zram->mem_pool, handle);
+
+	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_obj_size(zram, index, 0);
+	WARN_ON_ONCE(zram->table[index].flags &
+		~(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)
+{
+	struct zcomp_strm *zstrm;
+	unsigned long handle;
+	unsigned int size;
+	void *src, *dst;
+	int ret;
+
+	zram_slot_lock(zram, index);
+	if (zram_test_flag(zram, index, ZRAM_WB)) {
+		struct bio_vec bvec;
+
+		zram_slot_unlock(zram, index);
+
+		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;
+		void *mem;
+
+		value = handle ? zram_get_element(zram, index) : 0;
+		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);
+
+	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
+	if (size == PAGE_SIZE) {
+		dst = kmap_atomic(page);
+		memcpy(dst, src, PAGE_SIZE);
+		kunmap_atomic(dst);
+		ret = 0;
+	} else {
+		dst = kmap_atomic(page);
+		ret = zcomp_decompress(zstrm, src, size, dst);
+		kunmap_atomic(dst);
+		zcomp_stream_put(zram->comp);
+	}
+	zs_unmap_object(zram->mem_pool, handle);
+	zram_slot_unlock(zram, index);
+
+	/* Should NEVER happen. Return bio error if it does. */
+	if (WARN_ON(ret))
+		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)
+{
+	int ret;
+	struct page *page;
+
+	page = bvec->bv_page;
+	if (is_partial_io(bvec)) {
+		/* Use a temporary buffer to decompress the page */
+		page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
+		if (!page)
+			return -ENOMEM;
+	}
+
+	ret = __zram_bvec_read(zram, page, index, bio, is_partial_io(bvec));
+	if (unlikely(ret))
+		goto out;
+
+	if (is_partial_io(bvec)) {
+		void *dst = kmap_atomic(bvec->bv_page);
+		void *src = kmap_atomic(page);
+
+		memcpy(dst + bvec->bv_offset, src + offset, bvec->bv_len);
+		kunmap_atomic(src);
+		kunmap_atomic(dst);
+	}
+out:
+	if (is_partial_io(bvec))
+		__free_page(page);
+
+	return ret;
+}
+
+static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
+				u32 index, struct bio *bio)
+{
+	int ret = 0;
+	unsigned long alloced_pages;
+	unsigned long handle = 0;
+	unsigned int comp_len = 0;
+	void *src, *dst, *mem;
+	struct zcomp_strm *zstrm;
+	struct page *page = bvec->bv_page;
+	unsigned long element = 0;
+	enum zram_pageflags flags = 0;
+
+	mem = kmap_atomic(page);
+	if (page_same_filled(mem, &element)) {
+		kunmap_atomic(mem);
+		/* Free memory associated with this sector now. */
+		flags = ZRAM_SAME;
+		atomic64_inc(&zram->stats.same_pages);
+		goto out;
+	}
+	kunmap_atomic(mem);
+
+compress_again:
+	zstrm = zcomp_stream_get(zram->comp);
+	src = kmap_atomic(page);
+	ret = zcomp_compress(zstrm, src, &comp_len);
+	kunmap_atomic(src);
+
+	if (unlikely(ret)) {
+		zcomp_stream_put(zram->comp);
+		pr_err("Compression failed! err=%d\n", ret);
+		zs_free(zram->mem_pool, handle);
+		return ret;
+	}
+
+	if (comp_len >= huge_class_size)
+		comp_len = PAGE_SIZE;
+	/*
+	 * handle 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.
+	 *
+	 * if we have a 'non-null' handle here then we are coming
+	 * from the slow path and handle has already been allocated.
+	 */
+	if (!handle)
+		handle = zs_malloc(zram->mem_pool, comp_len,
+				__GFP_KSWAPD_RECLAIM |
+				__GFP_NOWARN |
+				__GFP_HIGHMEM |
+				__GFP_MOVABLE);
+	if (!handle) {
+		zcomp_stream_put(zram->comp);
+		atomic64_inc(&zram->stats.writestall);
+		handle = zs_malloc(zram->mem_pool, comp_len,
+				GFP_NOIO | __GFP_HIGHMEM |
+				__GFP_MOVABLE);
+		if (handle)
+			goto compress_again;
+		return -ENOMEM;
+	}
+
+	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);
+		zs_free(zram->mem_pool, handle);
+		return -ENOMEM;
+	}
+
+	dst = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
+
+	src = zstrm->buffer;
+	if (comp_len == PAGE_SIZE)
+		src = kmap_atomic(page);
+	memcpy(dst, src, comp_len);
+	if (comp_len == PAGE_SIZE)
+		kunmap_atomic(src);
+
+	zcomp_stream_put(zram->comp);
+	zs_unmap_object(zram->mem_pool, handle);
+	atomic64_add(comp_len, &zram->stats.compr_data_size);
+out:
+	/*
+	 * Free memory associated with this sector
+	 * before overwriting unused sectors.
+	 */
+	zram_slot_lock(zram, index);
+	zram_free_page(zram, index);
+
+	if (comp_len == PAGE_SIZE) {
+		zram_set_flag(zram, index, ZRAM_HUGE);
+		atomic64_inc(&zram->stats.huge_pages);
+	}
+
+	if (flags) {
+		zram_set_flag(zram, index, flags);
+		zram_set_element(zram, index, element);
+	}  else {
+		zram_set_handle(zram, index, handle);
+		zram_set_obj_size(zram, index, comp_len);
+	}
+	zram_slot_unlock(zram, index);
+
+	/* Update stats */
+	atomic64_inc(&zram->stats.pages_stored);
+	return ret;
+}
+
+static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
+				u32 index, int offset, struct bio *bio)
+{
+	int ret;
+	struct page *page = NULL;
+	void *src;
+	struct bio_vec vec;
+
+	vec = *bvec;
+	if (is_partial_io(bvec)) {
+		void *dst;
+		/*
+		 * This is a partial IO. We need to read the full page
+		 * before to write the changes.
+		 */
+		page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
+		if (!page)
+			return -ENOMEM;
+
+		ret = __zram_bvec_read(zram, page, index, bio, true);
+		if (ret)
+			goto out;
+
+		src = kmap_atomic(bvec->bv_page);
+		dst = kmap_atomic(page);
+		memcpy(dst + offset, src + bvec->bv_offset, bvec->bv_len);
+		kunmap_atomic(dst);
+		kunmap_atomic(src);
+
+		vec.bv_page = page;
+		vec.bv_len = PAGE_SIZE;
+		vec.bv_offset = 0;
+	}
+
+	ret = __zram_bvec_write(zram, &vec, index, bio);
+out:
+	if (is_partial_io(bvec))
+		__free_page(page);
+	return ret;
+}
+
+/*
+ * zram_bio_discard - handler on discard request
+ * @index: physical block index in PAGE_SIZE units
+ * @offset: byte offset within physical block
+ */
+static void zram_bio_discard(struct zram *zram, u32 index,
+			     int offset, struct bio *bio)
+{
+	size_t n = bio->bi_iter.bi_size;
+
+	/*
+	 * zram manages data in physical block size units. Because logical block
+	 * size isn't identical with physical block size on some arch, we
+	 * could get a discard request pointing to a specific offset within a
+	 * certain physical block.  Although we can handle this request by
+	 * reading that physiclal block and decompressing and partially zeroing
+	 * and re-compressing and then re-storing it, this isn't reasonable
+	 * because our intent with a discard request is to save memory.  So
+	 * skipping this logical block is appropriate here.
+	 */
+	if (offset) {
+		if (n <= (PAGE_SIZE - offset))
+			return;
+
+		n -= (PAGE_SIZE - offset);
+		index++;
+	}
+
+	while (n >= PAGE_SIZE) {
+		zram_slot_lock(zram, index);
+		zram_free_page(zram, index);
+		zram_slot_unlock(zram, index);
+		atomic64_inc(&zram->stats.notify_free);
+		index++;
+		n -= PAGE_SIZE;
+	}
+}
+
+/*
+ * Returns errno if it has some problem. Otherwise return 0 or 1.
+ * Returns 0 if IO request was done synchronously
+ * Returns 1 if IO request was successfully submitted.
+ */
+static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
+			int offset, unsigned int op, struct bio *bio)
+{
+	int ret;
+
+	if (!op_is_write(op)) {
+		atomic64_inc(&zram->stats.num_reads);
+		ret = zram_bvec_read(zram, bvec, index, offset, bio);
+		flush_dcache_page(bvec->bv_page);
+	} else {
+		atomic64_inc(&zram->stats.num_writes);
+		ret = zram_bvec_write(zram, bvec, index, offset, bio);
+	}
+
+	zram_slot_lock(zram, index);
+	zram_accessed(zram, index);
+	zram_slot_unlock(zram, index);
+
+	if (unlikely(ret < 0)) {
+		if (!op_is_write(op))
+			atomic64_inc(&zram->stats.failed_reads);
+		else
+			atomic64_inc(&zram->stats.failed_writes);
+	}
+
+	return ret;
+}
+
+static void __zram_make_request(struct zram *zram, struct bio *bio)
+{
+	int offset;
+	u32 index;
+	struct bio_vec bvec;
+	struct bvec_iter iter;
+	unsigned long start_time;
+
+	index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
+	offset = (bio->bi_iter.bi_sector &
+		  (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;
+
+	switch (bio_op(bio)) {
+	case REQ_OP_DISCARD:
+	case REQ_OP_WRITE_ZEROES:
+		zram_bio_discard(zram, index, offset, bio);
+		bio_endio(bio);
+		return;
+	default:
+		break;
+	}
+
+	start_time = bio_start_io_acct(bio);
+	bio_for_each_segment(bvec, bio, iter) {
+		struct bio_vec bv = bvec;
+		unsigned int unwritten = bvec.bv_len;
+
+		do {
+			bv.bv_len = min_t(unsigned int, PAGE_SIZE - offset,
+							unwritten);
+			if (zram_bvec_rw(zram, &bv, index, offset,
+					 bio_op(bio), bio) < 0) {
+				bio->bi_status = BLK_STS_IOERR;
+				break;
+			}
+
+			bv.bv_offset += bv.bv_len;
+			unwritten -= bv.bv_len;
+
+			update_position(&index, &offset, &bv);
+		} while (unwritten);
+	}
+	bio_end_io_acct(bio, start_time);
+	bio_endio(bio);
+}
+
+/*
+ * Handler function for all zram I/O requests.
+ */
+static blk_qc_t zram_submit_bio(struct bio *bio)
+{
+	struct zram *zram = bio->bi_disk->private_data;
+
+	if (!valid_io_request(zram, bio->bi_iter.bi_sector,
+					bio->bi_iter.bi_size)) {
+		atomic64_inc(&zram->stats.invalid_io);
+		goto error;
+	}
+
+	__zram_make_request(zram, bio);
+	return BLK_QC_T_NONE;
+
+error:
+	bio_io_error(bio);
+	return BLK_QC_T_NONE;
+}
+
+static void zram_slot_free_notify(struct block_device *bdev,
+				unsigned long index)
+{
+	struct zram *zram;
+
+	zram = bdev->bd_disk->private_data;
+
+	atomic64_inc(&zram->stats.notify_free);
+	if (!zram_slot_trylock(zram, index)) {
+		atomic64_inc(&zram->stats.miss_free);
+		return;
+	}
+
+	zram_free_page(zram, index);
+	zram_slot_unlock(zram, index);
+}
+
+static int zram_rw_page(struct block_device *bdev, sector_t sector,
+		       struct page *page, unsigned int op)
+{
+	int offset, ret;
+	u32 index;
+	struct zram *zram;
+	struct bio_vec bv;
+	unsigned long start_time;
+
+	if (PageTransHuge(page))
+		return -ENOTSUPP;
+	zram = bdev->bd_disk->private_data;
+
+	if (!valid_io_request(zram, sector, PAGE_SIZE)) {
+		atomic64_inc(&zram->stats.invalid_io);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	index = sector >> SECTORS_PER_PAGE_SHIFT;
+	offset = (sector & (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;
+
+	bv.bv_page = page;
+	bv.bv_len = PAGE_SIZE;
+	bv.bv_offset = 0;
+
+	start_time = disk_start_io_acct(bdev->bd_disk, SECTORS_PER_PAGE, op);
+	ret = zram_bvec_rw(zram, &bv, index, offset, op, NULL);
+	disk_end_io_acct(bdev->bd_disk, op, start_time);
+out:
+	/*
+	 * If I/O fails, just return error(ie, non-zero) without
+	 * calling page_endio.
+	 * It causes resubmit the I/O with bio request by upper functions
+	 * of rw_page(e.g., swap_readpage, __swap_writepage) and
+	 * bio->bi_end_io does things to handle the error
+	 * (e.g., SetPageError, set_page_dirty and extra works).
+	 */
+	if (unlikely(ret < 0))
+		return ret;
+
+	switch (ret) {
+	case 0:
+		page_endio(page, op_is_write(op), 0);
+		break;
+	case 1:
+		ret = 0;
+		break;
+	default:
+		WARN_ON(1);
+	}
+	return ret;
+}
+
+static void zram_reset_device(struct zram *zram)
+{
+	struct zcomp *comp;
+	u64 disksize;
+
+	down_write(&zram->init_lock);
+
+	zram->limit_pages = 0;
+
+	if (!init_done(zram)) {
+		up_write(&zram->init_lock);
+		return;
+	}
+
+	comp = zram->comp;
+	disksize = zram->disksize;
+	zram->disksize = 0;
+
+	set_capacity(zram->disk, 0);
+	part_stat_set_all(&zram->disk->part0, 0);
+
+	up_write(&zram->init_lock);
+	/* I/O operation under all of CPU are done so let's free */
+	zram_meta_free(zram, disksize);
+	memset(&zram->stats, 0, sizeof(zram->stats));
+	zcomp_destroy(comp);
+	reset_bdev(zram);
+}
+
+static ssize_t disksize_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	u64 disksize;
+	struct zcomp *comp;
+	struct zram *zram = dev_to_zram(dev);
+	int err;
+
+	disksize = memparse(buf, NULL);
+	if (!disksize)
+		return -EINVAL;
+
+	down_write(&zram->init_lock);
+	if (init_done(zram)) {
+		pr_info("Cannot change disksize for initialized device\n");
+		err = -EBUSY;
+		goto out_unlock;
+	}
+
+	disksize = PAGE_ALIGN(disksize);
+	if (!zram_meta_alloc(zram, disksize)) {
+		err = -ENOMEM;
+		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;
+	}
+
+	zram->comp = comp;
+	zram->disksize = disksize;
+	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
+
+	revalidate_disk_size(zram->disk, true);
+	up_write(&zram->init_lock);
+
+	return len;
+
+out_free_meta:
+	zram_meta_free(zram, disksize);
+out_unlock:
+	up_write(&zram->init_lock);
+	return err;
+}
+
+static ssize_t reset_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	int ret;
+	unsigned short do_reset;
+	struct zram *zram;
+	struct block_device *bdev;
+
+	ret = kstrtou16(buf, 10, &do_reset);
+	if (ret)
+		return ret;
+
+	if (!do_reset)
+		return -EINVAL;
+
+	zram = dev_to_zram(dev);
+	bdev = bdget_disk(zram->disk, 0);
+	if (!bdev)
+		return -ENOMEM;
+
+	mutex_lock(&bdev->bd_mutex);
+	/* Do not reset an active device or claimed device */
+	if (bdev->bd_openers || zram->claim) {
+		mutex_unlock(&bdev->bd_mutex);
+		bdput(bdev);
+		return -EBUSY;
+	}
+
+	/* From now on, anyone can't open /dev/zram[0-9] */
+	zram->claim = true;
+	mutex_unlock(&bdev->bd_mutex);
+
+	/* Make sure all the pending I/O are finished */
+	fsync_bdev(bdev);
+	zram_reset_device(zram);
+	revalidate_disk_size(zram->disk, true);
+	bdput(bdev);
+
+	mutex_lock(&bdev->bd_mutex);
+	zram->claim = false;
+	mutex_unlock(&bdev->bd_mutex);
+
+	return len;
+}
+
+static int zram_open(struct block_device *bdev, fmode_t mode)
+{
+	int ret = 0;
+	struct zram *zram;
+
+	WARN_ON(!mutex_is_locked(&bdev->bd_mutex));
+
+	zram = bdev->bd_disk->private_data;
+	/* zram was claimed to reset so open request fails */
+	if (zram->claim)
+		ret = -EBUSY;
+
+	return ret;
+}
+
+static const struct block_device_operations zram_devops = {
+	.open = zram_open,
+	.submit_bio = zram_submit_bio,
+	.swap_slot_free_notify = zram_slot_free_notify,
+	.rw_page = zram_rw_page,
+	.owner = THIS_MODULE
+};
+
+static const struct block_device_operations zram_wb_devops = {
+	.open = zram_open,
+	.submit_bio = zram_submit_bio,
+	.swap_slot_free_notify = zram_slot_free_notify,
+	.owner = THIS_MODULE
+};
+
+static DEVICE_ATTR_WO(compact);
+static DEVICE_ATTR_RW(disksize);
+static DEVICE_ATTR_RO(initstate);
+static DEVICE_ATTR_WO(reset);
+static DEVICE_ATTR_WO(mem_limit);
+static DEVICE_ATTR_WO(mem_used_max);
+static DEVICE_ATTR_WO(idle);
+static DEVICE_ATTR_RW(max_comp_streams);
+static DEVICE_ATTR_RW(comp_algorithm);
+#ifdef CONFIG_ZRAM_WRITEBACK
+static DEVICE_ATTR_RW(backing_dev);
+static DEVICE_ATTR_WO(writeback);
+static DEVICE_ATTR_RW(writeback_limit);
+static DEVICE_ATTR_RW(writeback_limit_enable);
+#endif
+
+static struct attribute *zram_disk_attrs[] = {
+	&dev_attr_disksize.attr,
+	&dev_attr_initstate.attr,
+	&dev_attr_reset.attr,
+	&dev_attr_compact.attr,
+	&dev_attr_mem_limit.attr,
+	&dev_attr_mem_used_max.attr,
+	&dev_attr_idle.attr,
+	&dev_attr_max_comp_streams.attr,
+	&dev_attr_comp_algorithm.attr,
+#ifdef CONFIG_ZRAM_WRITEBACK
+	&dev_attr_backing_dev.attr,
+	&dev_attr_writeback.attr,
+	&dev_attr_writeback_limit.attr,
+	&dev_attr_writeback_limit_enable.attr,
+#endif
+	&dev_attr_io_stat.attr,
+	&dev_attr_mm_stat.attr,
+#ifdef CONFIG_ZRAM_WRITEBACK
+	&dev_attr_bd_stat.attr,
+#endif
+	&dev_attr_debug_stat.attr,
+	NULL,
+};
+
+static const struct attribute_group zram_disk_attr_group = {
+	.attrs = zram_disk_attrs,
+};
+
+static const struct attribute_group *zram_disk_attr_groups[] = {
+	&zram_disk_attr_group,
+	NULL,
+};
+
+/*
+ * Allocate and initialize new zram device. the function returns
+ * '>= 0' device_id upon success, and negative value otherwise.
+ */
+static int zram_add(void)
+{
+	struct zram *zram;
+	struct request_queue *queue;
+	int ret, device_id;
+
+	zram = kzalloc(sizeof(struct zram), GFP_KERNEL);
+	if (!zram)
+		return -ENOMEM;
+
+	ret = idr_alloc(&zram_index_idr, zram, 0, 0, GFP_KERNEL);
+	if (ret < 0)
+		goto out_free_dev;
+	device_id = ret;
+
+	init_rwsem(&zram->init_lock);
+#ifdef CONFIG_ZRAM_WRITEBACK
+	spin_lock_init(&zram->wb_limit_lock);
+#endif
+	queue = blk_alloc_queue(NUMA_NO_NODE);
+	if (!queue) {
+		pr_err("Error allocating disk queue for device %d\n",
+			device_id);
+		ret = -ENOMEM;
+		goto out_free_idr;
+	}
+
+	/* gendisk structure */
+	zram->disk = alloc_disk(1);
+	if (!zram->disk) {
+		pr_err("Error allocating disk structure for device %d\n",
+			device_id);
+		ret = -ENOMEM;
+		goto out_free_queue;
+	}
+
+	zram->disk->major = zram_major;
+	zram->disk->first_minor = device_id;
+	zram->disk->fops = &zram_devops;
+	zram->disk->queue = queue;
+	zram->disk->private_data = zram;
+	snprintf(zram->disk->disk_name, 16, "zram%d", device_id);
+
+	/* Actual capacity set using syfs (/sys/block/zram<id>/disksize */
+	set_capacity(zram->disk, 0);
+	/* zram devices sort of resembles non-rotational disks */
+	blk_queue_flag_set(QUEUE_FLAG_NONROT, zram->disk->queue);
+	blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, zram->disk->queue);
+
+	/*
+	 * To ensure that we always get PAGE_SIZE aligned
+	 * and n*PAGE_SIZED sized I/O requests.
+	 */
+	blk_queue_physical_block_size(zram->disk->queue, PAGE_SIZE);
+	blk_queue_logical_block_size(zram->disk->queue,
+					ZRAM_LOGICAL_BLOCK_SIZE);
+	blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
+	blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);
+	zram->disk->queue->limits.discard_granularity = PAGE_SIZE;
+	blk_queue_max_discard_sectors(zram->disk->queue, UINT_MAX);
+	blk_queue_flag_set(QUEUE_FLAG_DISCARD, zram->disk->queue);
+
+	/*
+	 * zram_bio_discard() will clear all logical blocks if logical block
+	 * size is identical with physical block size(PAGE_SIZE). But if it is
+	 * different, we will skip discarding some parts of logical blocks in
+	 * the part of the request range which isn't aligned to physical block
+	 * size.  So we can't ensure that all discarded logical blocks are
+	 * zeroed.
+	 */
+	if (ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE)
+		blk_queue_max_write_zeroes_sectors(zram->disk->queue, UINT_MAX);
+
+	blk_queue_flag_set(QUEUE_FLAG_STABLE_WRITES, zram->disk->queue);
+	device_add_disk(NULL, zram->disk, zram_disk_attr_groups);
+
+	strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));
+
+	zram_debugfs_register(zram);
+	pr_info("Added device: %s\n", zram->disk->disk_name);
+	return device_id;
+
+out_free_queue:
+	blk_cleanup_queue(queue);
+out_free_idr:
+	idr_remove(&zram_index_idr, device_id);
+out_free_dev:
+	kfree(zram);
+	return ret;
+}
+
+static int zram_remove(struct zram *zram)
+{
+	struct block_device *bdev;
+
+	bdev = bdget_disk(zram->disk, 0);
+	if (!bdev)
+		return -ENOMEM;
+
+	mutex_lock(&bdev->bd_mutex);
+	if (bdev->bd_openers || zram->claim) {
+		mutex_unlock(&bdev->bd_mutex);
+		bdput(bdev);
+		return -EBUSY;
+	}
+
+	zram->claim = true;
+	mutex_unlock(&bdev->bd_mutex);
+
+	zram_debugfs_unregister(zram);
+
+	/* Make sure all the pending I/O are finished */
+	fsync_bdev(bdev);
+	zram_reset_device(zram);
+	bdput(bdev);
+
+	pr_info("Removed device: %s\n", zram->disk->disk_name);
+
+	del_gendisk(zram->disk);
+	blk_cleanup_queue(zram->disk->queue);
+	put_disk(zram->disk);
+	kfree(zram);
+	return 0;
+}
+
+/* zram-control sysfs attributes */
+
+/*
+ * NOTE: hot_add attribute is not the usual read-only sysfs attribute. In a
+ * sense that reading from this file does alter the state of your system -- it
+ * creates a new un-initialized zram device and returns back this device's
+ * device_id (or an error code if it fails to create a new device).
+ */
+static ssize_t hot_add_show(struct class *class,
+			struct class_attribute *attr,
+			char *buf)
+{
+	int ret;
+
+	mutex_lock(&zram_index_mutex);
+	ret = zram_add();
+	mutex_unlock(&zram_index_mutex);
+
+	if (ret < 0)
+		return ret;
+	return scnprintf(buf, PAGE_SIZE, "%d\n", ret);
+}
+static struct class_attribute class_attr_hot_add =
+	__ATTR(hot_add, 0400, hot_add_show, NULL);
+
+static ssize_t hot_remove_store(struct class *class,
+			struct class_attribute *attr,
+			const char *buf,
+			size_t count)
+{
+	struct zram *zram;
+	int ret, dev_id;
+
+	/* dev_id is gendisk->first_minor, which is `int' */
+	ret = kstrtoint(buf, 10, &dev_id);
+	if (ret)
+		return ret;
+	if (dev_id < 0)
+		return -EINVAL;
+
+	mutex_lock(&zram_index_mutex);
+
+	zram = idr_find(&zram_index_idr, dev_id);
+	if (zram) {
+		ret = zram_remove(zram);
+		if (!ret)
+			idr_remove(&zram_index_idr, dev_id);
+	} else {
+		ret = -ENODEV;
+	}
+
+	mutex_unlock(&zram_index_mutex);
+	return ret ? ret : count;
+}
+static CLASS_ATTR_WO(hot_remove);
+
+static struct attribute *zram_control_class_attrs[] = {
+	&class_attr_hot_add.attr,
+	&class_attr_hot_remove.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(zram_control_class);
+
+static struct class zram_control_class = {
+	.name		= "zram-control",
+	.owner		= THIS_MODULE,
+	.class_groups	= zram_control_class_groups,
+};
+
+static int zram_remove_cb(int id, void *ptr, void *data)
+{
+	zram_remove(ptr);
+	return 0;
+}
+
+static void destroy_devices(void)
+{
+	class_unregister(&zram_control_class);
+	idr_for_each(&zram_index_idr, &zram_remove_cb, NULL);
+	zram_debugfs_destroy();
+	idr_destroy(&zram_index_idr);
+	unregister_blkdev(zram_major, "zram");
+	cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
+}
+
+static int __init zram_init(void)
+{
+	int ret;
+
+	ret = cpuhp_setup_state_multi(CPUHP_ZCOMP_PREPARE, "block/zram:prepare",
+				      zcomp_cpu_up_prepare, zcomp_cpu_dead);
+	if (ret < 0)
+		return ret;
+
+	ret = class_register(&zram_control_class);
+	if (ret) {
+		pr_err("Unable to register zram-control class\n");
+		cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
+		return ret;
+	}
+
+	zram_debugfs_create();
+	zram_major = register_blkdev(0, "zram");
+	if (zram_major <= 0) {
+		pr_err("Unable to get major number\n");
+		class_unregister(&zram_control_class);
+		cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
+		return -EBUSY;
+	}
+
+	while (num_devices != 0) {
+		mutex_lock(&zram_index_mutex);
+		ret = zram_add();
+		mutex_unlock(&zram_index_mutex);
+		if (ret < 0)
+			goto out_error;
+		num_devices--;
+	}
+
+	return 0;
+
+out_error:
+	destroy_devices();
+	return ret;
+}
+
+static void __exit zram_exit(void)
+{
+	destroy_devices();
+}
+
+module_init(zram_init);
+module_exit(zram_exit);
+
+module_param(num_devices, uint, 0);
+MODULE_PARM_DESC(num_devices, "Number of pre-created zram devices");
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");
+MODULE_DESCRIPTION("Compressed RAM Block Device");
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
new file mode 100644
index 000000000..f2fd46daa
--- /dev/null
+++ b/drivers/block/zram/zram_drv.h
@@ -0,0 +1,129 @@
+/*
+ * Compressed RAM block device
+ *
+ * Copyright (C) 2008, 2009, 2010  Nitin Gupta
+ *               2012, 2013 Minchan Kim
+ *
+ * This code is released using a dual license strategy: BSD/GPL
+ * You can choose the licence that better fits your requirements.
+ *
+ * Released under the terms of 3-clause BSD License
+ * Released under the terms of GNU General Public License Version 2.0
+ *
+ */
+
+#ifndef _ZRAM_DRV_H_
+#define _ZRAM_DRV_H_
+
+#include <linux/rwsem.h>
+#include <linux/zsmalloc.h>
+#include <linux/crypto.h>
+
+#include "zcomp.h"
+
+#define SECTORS_PER_PAGE_SHIFT	(PAGE_SHIFT - SECTOR_SHIFT)
+#define SECTORS_PER_PAGE	(1 << SECTORS_PER_PAGE_SHIFT)
+#define ZRAM_LOGICAL_BLOCK_SHIFT 12
+#define ZRAM_LOGICAL_BLOCK_SIZE	(1 << ZRAM_LOGICAL_BLOCK_SHIFT)
+#define ZRAM_SECTOR_PER_LOGICAL_BLOCK	\
+	(1 << (ZRAM_LOGICAL_BLOCK_SHIFT - SECTOR_SHIFT))
+
+
+/*
+ * The lower ZRAM_FLAG_SHIFT bits of table.flags is for
+ * object size (excluding header), the higher bits is for
+ * zram_pageflags.
+ *
+ * zram is mainly used for memory efficiency so we want to keep memory
+ * footprint small so we can squeeze size and flags into a field.
+ * The lower ZRAM_FLAG_SHIFT bits is for object size (excluding header),
+ * the higher bits is for zram_pageflags.
+ */
+#define ZRAM_FLAG_SHIFT 24
+
+/* Flags for zram pages (table[page_no].flags) */
+enum zram_pageflags {
+	/* zram slot is locked */
+	ZRAM_LOCK = ZRAM_FLAG_SHIFT,
+	ZRAM_SAME,	/* Page consists the same element */
+	ZRAM_WB,	/* page is stored on backing_device */
+	ZRAM_UNDER_WB,	/* page is under writeback */
+	ZRAM_HUGE,	/* Incompressible page */
+	ZRAM_IDLE,	/* not accessed page since last idle marking */
+
+	__NR_ZRAM_PAGEFLAGS,
+};
+
+/*-- Data structures */
+
+/* Allocated for each disk page */
+struct zram_table_entry {
+	union {
+		unsigned long handle;
+		unsigned long element;
+	};
+	unsigned long flags;
+#ifdef CONFIG_ZRAM_MEMORY_TRACKING
+	ktime_t ac_time;
+#endif
+};
+
+struct zram_stats {
+	atomic64_t compr_data_size;	/* compressed size of pages stored */
+	atomic64_t num_reads;	/* failed + successful */
+	atomic64_t num_writes;	/* --do-- */
+	atomic64_t failed_reads;	/* can happen when memory is too low */
+	atomic64_t failed_writes;	/* can happen when memory is too low */
+	atomic64_t invalid_io;	/* non-page-aligned I/O requests */
+	atomic64_t notify_free;	/* no. of swap slot free notifications */
+	atomic64_t same_pages;		/* no. of same element filled pages */
+	atomic64_t huge_pages;		/* no. of huge pages */
+	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 miss_free;		/* no. of missed free */
+#ifdef	CONFIG_ZRAM_WRITEBACK
+	atomic64_t bd_count;		/* no. of pages in backing device */
+	atomic64_t bd_reads;		/* no. of reads from backing device */
+	atomic64_t bd_writes;		/* no. of writes from backing device */
+#endif
+};
+
+struct zram {
+	struct zram_table_entry *table;
+	struct zs_pool *mem_pool;
+	struct zcomp *comp;
+	struct gendisk *disk;
+	/* Prevent concurrent execution of device init */
+	struct rw_semaphore init_lock;
+	/*
+	 * the number of pages zram can consume for storing compressed data
+	 */
+	unsigned long limit_pages;
+
+	struct zram_stats stats;
+	/*
+	 * This is the limit on amount of *uncompressed* worth of data
+	 * we can store in a disk.
+	 */
+	u64 disksize;	/* bytes */
+	char compressor[CRYPTO_MAX_ALG_NAME];
+	/*
+	 * zram is claimed so open request will be failed
+	 */
+	bool claim; /* Protected by bdev->bd_mutex */
+	struct file *backing_dev;
+#ifdef CONFIG_ZRAM_WRITEBACK
+	spinlock_t wb_limit_lock;
+	bool wb_limit_enable;
+	u64 bd_wb_limit;
+	struct block_device *bdev;
+	unsigned int old_block_size;
+	unsigned long *bitmap;
+	unsigned long nr_pages;
+#endif
+#ifdef CONFIG_ZRAM_MEMORY_TRACKING
+	struct dentry *debugfs_dir;
+#endif
+};
+#endif