[PATCH v4 1/1] DM: inplace compressed DM target

[Ram Pai]

This is a simple DM target supporting inplace compression. Its best
suited for SSD. The underlying disk must support 512B sector size.
The target only supports 4k sector size.

Disk layout:
|super|...meta...|..data...|

Store unit is 4k (a block). Super is 1 block, which stores meta  and
data size and compression algorithm. Meta is a bitmap. For each data
 block, there are 5 bits meta.

Data:

Data of   a block is compressed. Compressed  data  is round up to 512B,
which is the payload. In disk, payload is  stored at  the beginning of
logical sector  of the block. Let's look  at an example.  Say we store
data to block A, which  is in sector  B(A*8), its orginal  size is 4k,
compressed size is  1500.    Compressed     data (CD)  will  use three
sectors (512B). The three  sectors  are the  payload. Payload  will be
stored at sector B.

---------------------------------------------------
... | CD1 | CD2 | CD3 |   |   |   |   |    | ...
---------------------------------------------------
    ^B    ^B+1  ^B+2                  ^B+7 ^B+8

For this block, we will not use sector B+3 to B+7 (a hole). We use four
meta  bits  to  present payload  size. The compressed size (1500) isn't
stored in meta directly. Instead, we  store  it  at  the last 32bits of
payload. In this  example, we store it at the  end  of  sector  B+2. If
compressed size + sizeof(32bits)  crosses a   sector, payload size will
increase one sector.  If payload  uses 8 sectors, we store uncompressed
data directly.

If IO size is bigger than one block, we can store the data as an extent.
Data of the  whole extent will compressed and stored in the similar way
like above.  The first  block of the extent is the head, all others are
the tail.  If extent is 1 block,  the  block  is head. We have 1 bit of
meta to present if a  block  is  head  or  tail. If 4 meta bits of head
block can't  store  extent payload size, we will borrow tail block meta
bits to  store  payload  size.   Max  allowd extent size is 128k, so we
don't compress/decompress too big size data.

Meta:
Modifying   data   will modify meta too. Meta will be written(flush) to
disk   depending   on   meta   write   policy. We support writeback and
writethrough mode.  In  writeback mode, meta will be written to disk in
an interval or a  FLUSH  request.  In  writethrough mode, data and meta
data will be written to disk together.

Advantages:

1. Simple. Since  we  store  compressed  data  in-place,  we don't need
   complicated disk data management.
2. Efficient. For  each  4k, we only need 5 bits meta. 1T data will use
less than 200M meta, so we  can  load  all meta into memory. And actual
compression size is in payload. So   if  IO doesn't need RMW and we use
writeback meta flush, we don't  need  extra IO for meta.

Disadvantages:

1. hole. Since we   store  compressed data in-place, there are a lot of
   holes (in above  example,  B+3 - B+7) Hole can impact IO, because we
   can't do IO merge.

2. 1:1 size. Compression  doesn't  change disk  size. If disk is 1T, we
   can only store 1T data even we do compression.

But this is for SSD only. Generally SSD firmware has a FTL layer to map
disk  sectors  to flash nand. High end SSD firmware has filesystem-like
FTL.

1. hole. Disk has a lot of holes, but SSD FTL   can   still  store data
   contiguous in nand. Even if we can't do IO   merge in  OS layer, SSD
   firmware can do it.

2. 1:1 size. On one side, we write compressed data to SSD, which means
   less  data is  written to SSD. This will be very helpful to improve
   SSD garbage collection, and  so write speed and life cycle. So even
   this is a problem, the target  is still helpful. On the other side,
   advanced SSD FTL can easily do thin provision. For example, if nand
   is   1T   and   we   let   SSD   report   it   as   2T,   and   use
   the  SSD  as  compressed target. In such SSD, we don't have the 1:1
   size issue.

So even if   SSD   FTL   cannot   map   non-contiguous disk sectors to
contiguous nand, the compression target can still function well.


Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
Signed-off-by: Ram Pai <ram.n.pai@xxxxxxxxx>
---
 .../device-mapper/dm-inplace-compress.txt          |  155 ++
 drivers/md/Kconfig                                 |    6 +
 drivers/md/Makefile                                |    2 +
 drivers/md/dm-inplace-compress.c                   | 2220 ++++++++++++++++++++
 drivers/md/dm-inplace-compress.h                   |  187 ++
 5 files changed, 2570 insertions(+)
 create mode 100644 Documentation/device-mapper/dm-inplace-compress.txt
 create mode 100644 drivers/md/dm-inplace-compress.c
 create mode 100644 drivers/md/dm-inplace-compress.h

diff --git a/Documentation/device-mapper/dm-inplace-compress.txt b/Documentation/device-mapper/dm-inplace-compress.txt
new file mode 100644
index 0000000..1835369
--- /dev/null
+++ b/Documentation/device-mapper/dm-inplace-compress.txt
@@ -0,0 +1,155 @@
+Device-Mapper's "inplace-compress" target provides inplace compression of block
+devices using the kernel compression API.
+
+Parameters: <device path> \
+	[ <#opt_params writethough> ]
+	[ <#opt_params <writeback> <meta_commit_delay> ]
+	[ <#opt_params compressor> <type> ]
+	[ <#opt_params critical>  ]
+
+
+<writethrough>
+    Write data and metadata together.
+
+<writeback> <meta_commit_delay>
+    Write metadata every 'meta_commit_delay' interval.
+
+<device path>
+    This is the device that is going to be used as backend and contains the
+    compressed data.  You can specify it as a path like /dev/xxx or a device
+    number <major>:<minor>.
+
+<compressor> <type>
+    Choose the compressor algorithm. 'lzo' and '842'
+    compressors are supported.
+
+<critical>
+    Block device used in critical path.
+
+Example scripts
+===============
+
+create a inplace-compress block device using lzo compression. Write metadata
+and data together.
+[[
+#!/bin/sh
+# Create a inplace-compress device using dmsetup
+device=$1  #your backing storage eg: /dev/sdc1
+size=80000 #size of your new compressed block device
+dmsetup create comp1 --table "0 $size inplacecompress $device
+		writethrough compressor lzo"
+]]
+
+
+create a inplace-compress block device using nx-842 hardware compression. Write
+metadata periodially every 5sec.
+
+[[
+#!/bin/sh
+# Create a inplace-compress device using dmsetup
+device=$1  #your backing storage eg: /dev/sdc1
+size=80000 #size of your new compressed block device
+dmsetup create comp1 --table "0 $size inplacecompress $device
+		writeback 5 compressor 842"
+]]
+
+
+Create a inplace-compress block device. Device is used in critical path;
+ex: swap device.
+
+[[
+#!/bin/sh
+# Create a inplace-compress device using dmsetup
+device=$1  #your backing storage eg: /dev/sdc1
+size=80000 #size of your new compressed block device
+dmsetup create comp1 --table "0 $size inplacecompress $device critical"
+]]
+
+Description
+===========
+    This is a simple DM target supporting inplace compression. Its best suited for
+    SSD. The underlying disk must support 512B sector size, the target only
+    supports 4k sector size.
+
+    Disk layout:
+    |super|...meta...|..data...|
+
+    Store unit is 4k (a block). Super is 1 block, which stores meta and data
+    size and compression algorithm. Meta is a bitmap. For each data block,
+    there are 5 bits meta.
+
+    Data:
+
+    Data of a block is compressed. Compressed data is round up to 512B, which
+    is the payload. In disk, payload is stored at the beginning of logical
+    sector of the block. Let's look at an example. Say we store data to block
+    A, which is in sector B(A*8), its orginal size is 4k, compressed size is
+    1500. Compressed data (CD) will use 3 sectors (512B). The 3 sectors are the
+    payload. Payload will be stored at sector B.
+
+    ---------------------------------------------------
+    ... | CD1 | CD2 | CD3 |   |   |   |   |    | ...
+    ---------------------------------------------------
+        ^B    ^B+1  ^B+2                  ^B+7 ^B+8
+
+    For this block, we will not use sector B+3 to B+7 (a hole). We use 4 meta
+    bits to present payload size. The compressed size (1500) isn't stored in
+    meta directly. Instead, we store it at the last 32bits of payload. In this
+    example, we store it at the end of sector B+2. If compressed size +
+    sizeof(32bits) crosses a sector, payload size will increase one sector. If
+    payload uses 8 sectors, we store uncompressed data directly.
+
+    If IO size is bigger than one block, we can store the data as an extent.
+    Data of the whole extent will compressed and stored in the similar way like
+    above.  The first block of the extent is the head, all others are the tail.
+    If extent is 1 block, the block is head. We have 1 bit of meta to present
+    if a block is head or tail. If 4 meta bits of head block can't store extent
+    payload size, we will borrow tail block meta bits to store payload size.
+    Max allowd extent size is 128k, so we don't compress/decompress too big
+    size data.
+
+    Meta:
+    Modifying data will modify meta too. Meta will be written(flush) to disk
+    depending on meta write policy. We support writeback and writethrough mode.
+    In writeback mode, meta will be written to disk in an interval or a FLUSH
+    request.  In writethrough mode, data and meta data will be written to disk
+    together.
+
+    Advantages:
+
+    1. Simple. Since we store compressed data in-place, we don't need complicated
+    disk data management.
+    2. Efficient. For each 4k, we only need 5 bits meta. 1T data will use less than
+    200M meta, so we can load all meta into memory. And actual compression size is
+    in payload. So if IO doesn't need RMW and we use writeback meta flush, we don't
+    need extra IO for meta.
+
+    Disadvantages:
+
+    1. hole. Since we store compressed data in-place, there are a lot of holes
+    (in above example, B+3 - B+7) Hole can impact IO, because we can't do IO
+    merge.
+
+    2. 1:1 size. Compression doesn't change disk size. If disk is 1T, we can
+    only store 1T data even we do compression.
+
+    But this is for SSD only. Generally SSD firmware has a FTL layer to map
+    disk sectors to flash nand. High end SSD firmware has filesystem-like FTL.
+
+    1. hole. Disk has a lot of holes, but SSD FTL can still store data continuous
+    in nand. Even if we can't do IO merge in OS layer, SSD firmware can do it.
+
+    2. 1:1 size. On one side, we write compressed data to SSD, which means less
+    data is written to SSD. This will be very helpful to improve SSD garbage
+    collection, and so write speed and life cycle. So even this is a problem, the
+    target is still helpful. On the other side, advanced SSD FTL can easily do thin
+    provision. For example, if nand is 1T and we let SSD report it as 2T, and use
+    the SSD as compressed target. In such SSD, we don't have the 1:1 size issue.
+
+    So even if SSD FTL cannot map non-continuous disk sectors to continuous nand,
+    the compression target can still function well.
+
+
+Author:
+	Shaohua Li <shli@xxxxxxxxxxxx>
+	Ram Pai <linuxram@xxxxxxxxxx>
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index b7767da..2eece2a 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -508,4 +508,10 @@ config DM_LOG_WRITES
 
 	  If unsure, say N.
 
+config DM_INPLACE_COMPRESS
+	tristate "Inplace Compression target"
+	depends on BLK_DEV_DM
+	---help---
+	  Allow volume managers to compress data for SSD.
+
 endif # MD
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index 3cbda1a..4525482 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -59,6 +59,8 @@ obj-$(CONFIG_DM_CACHE_SMQ)	+= dm-cache-smq.o
 obj-$(CONFIG_DM_CACHE_CLEANER)	+= dm-cache-cleaner.o
 obj-$(CONFIG_DM_ERA)		+= dm-era.o
 obj-$(CONFIG_DM_LOG_WRITES)	+= dm-log-writes.o
+obj-$(CONFIG_DM_LOG_WRITES)	+= dm-log-writes.o
+obj-$(CONFIG_DM_INPLACE_COMPRESS)	+= dm-inplace-compress.o
 
 ifeq ($(CONFIG_DM_UEVENT),y)
 dm-mod-objs			+= dm-uevent.o
diff --git a/drivers/md/dm-inplace-compress.c b/drivers/md/dm-inplace-compress.c
new file mode 100644
index 0000000..41312d6
--- /dev/null
+++ b/drivers/md/dm-inplace-compress.c
@@ -0,0 +1,2220 @@
+/*
+ *  device mapper compression block device.
+ *
+ *  Released under GPL v2.
+ *
+ */
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+#include <linux/device-mapper.h>
+#include <linux/dm-io.h>
+#include <linux/crypto.h>
+#include <linux/lzo.h>
+#include <linux/kthread.h>
+#include <linux/page-flags.h>
+#include <linux/completion.h>
+#include <linux/vmalloc.h>
+#include "dm-inplace-compress.h"
+
+#define DM_MSG_PREFIX "dm-inplace-compress"
+
+
+static const struct kernel_param_ops dm_icomp_alloc_param_ops = {
+	.set    = param_set_ulong,
+	.get    = param_get_ulong,
+};
+
+static atomic64_t dm_icomp_total_alloc_size;
+#define DMCP_ALLOC(s) {atomic64_add(s, &dm_icomp_total_alloc_size); }
+#define DMCP_FREE_ALLOC(s) {atomic64_sub(s, &dm_icomp_total_alloc_size); }
+module_param_cb(dm_icomp_total_alloc_size, &dm_icomp_alloc_param_ops,
+				&dm_icomp_total_alloc_size, 0644);
+
+static atomic64_t dm_icomp_total_bio_save;
+#define DMCP_ALLOC_SAVE(s) {atomic64_add(s, &dm_icomp_total_bio_save); }
+module_param_cb(dm_icomp_total_bio_save, &dm_icomp_alloc_param_ops,
+				&dm_icomp_total_bio_save, 0644);
+
+
+static struct kmem_cache *dm_icomp_req_cachep;
+static struct kmem_cache *dm_icomp_io_range_cachep;
+static struct kmem_cache *dm_icomp_meta_io_cachep;
+
+static struct dm_icomp_io_worker dm_icomp_io_workers[NR_CPUS];
+static struct workqueue_struct *dm_icomp_wq;
+
+/*
+ *****************************************************
+ * compressor selection logic
+ *****************************************************
+ */
+static struct dm_icomp_compressor_data compressors[] = {
+	[DMCP_COMP_ALG_LZO] = {
+		.name = "lzo",
+		.can_handle_overflow = false,
+		.comp_len = lzo_comp_len,
+		.max_comp_len = lzo_max_comp_len,
+	},
+	[DMCP_COMP_ALG_842] = {
+		.name = "842",
+		.can_handle_overflow = true,
+		.comp_len = nx842_comp_len,
+		.max_comp_len = nx842_max_comp_len,
+	},
+};
+
+static int default_compressor = DMCP_COMP_ALG_LZO;
+#define DMCP_ALGO_LENGTH 9
+static char dm_icomp_algorithm[DMCP_ALGO_LENGTH] = "lzo";
+static struct kparam_string dm_icomp_compressor_kparam = {
+	.string =	dm_icomp_algorithm,
+	.maxlen =	sizeof(dm_icomp_algorithm),
+};
+static int dm_icomp_compressor_param_set(const char *,
+		const struct kernel_param *);
+static struct kernel_param_ops dm_icomp_compressor_param_ops = {
+	.set =	dm_icomp_compressor_param_set,
+	.get =	param_get_string,
+};
+module_param_cb(compress_algorithm, &dm_icomp_compressor_param_ops,
+		&dm_icomp_compressor_kparam, 0644);
+
+
+
+static int get_comp_id(const char *s)
+{
+	int r, val_len;
+
+	if (!crypto_has_comp(s, 0, 0))
+		return -1;
+
+	for (r = 0; r < ARRAY_SIZE(compressors); r++) {
+		val_len = strlen(compressors[r].name);
+		if (!strncmp(s, compressors[r].name, val_len))
+			return r;
+	}
+	return -1;
+}
+
+static const char *get_comp_name(int id)
+{
+	if (id < 0 || id > ARRAY_SIZE(compressors))
+		return NULL;
+	return compressors[id].name;
+}
+
+static void set_default_compressor(int index)
+{
+	default_compressor = index;
+	strlcpy(dm_icomp_algorithm, compressors[index].name,
+			sizeof(dm_icomp_algorithm));
+	DMINFO("compressor  is %s", dm_icomp_algorithm);
+}
+
+static inline int get_default_compressor(void)
+{
+	return default_compressor;
+}
+
+static int select_default_compressor(void)
+{
+	int r;
+	int arr_size = ARRAY_SIZE(compressors);
+
+	for (r = 0; r < arr_size; r++)
+		if (crypto_has_comp(compressors[r].name, 0, 0))
+			break;
+	if (r >= arr_size) {
+		DMWARN("No crypto compressors are supported");
+		return -EINVAL;
+	}
+	set_default_compressor(r);
+	return 0;
+}
+
+static int dm_icomp_compressor_param_set(const char *val,
+		const struct kernel_param *kp)
+{
+	int ret;
+	char str[kp->str->maxlen], *s;
+	int val_len = strlen(val)+1;
+
+	strlcpy(str, val, val_len);
+	s = strim(str);
+	ret = get_comp_id(s);
+	if (ret < 0) {
+		DMWARN("Compressor %s not supported", s);
+		return -1;
+	}
+	set_default_compressor(ret);
+	return 0;
+}
+
+static void free_compressor(struct dm_icomp_info *info)
+{
+	int i;
+
+	for_each_possible_cpu(i) {
+		if (info->tfm[i]) {
+			crypto_free_comp(info->tfm[i]);
+			info->tfm[i] = NULL;
+		}
+	}
+}
+
+static int alloc_compressor(struct dm_icomp_info *info)
+{
+	int i;
+	const char *alg_name = get_comp_name(info->comp_alg);
+
+	for_each_possible_cpu(i) {
+		info->tfm[i] = crypto_alloc_comp(
+			alg_name, 0, 0);
+		if (IS_ERR(info->tfm[i]))
+			goto err;
+	}
+	return 0;
+
+err:
+	free_compressor(info);
+	return -ENOMEM;
+}
+
+/**** END compressor select logic ****/
+
+
+/*****  metadata logic ***************/
+/*
+ * return the meta data bits corresponding to a block
+ * @block_index : the index of the block
+ */
+static u8 dm_icomp_get_meta(struct dm_icomp_info *info, u64 block_index)
+{
+	u64 first_bit = block_index * DMCP_META_BITS;
+	int bits, offset;
+	u32 data;
+	u8  ret = 0;
+
+	offset = first_bit & (DMCP_BITS_PER_ENTRY-1);
+	bits = min_t(u32, DMCP_META_BITS, DMCP_BITS_PER_ENTRY - offset);
+
+	data = (u32)info->meta_bitmap[first_bit >> DMCP_META_BITS];
+	ret = (data >> offset) & ((1 << bits) - 1);
+
+	if (bits < DMCP_META_BITS) {
+		data = info->meta_bitmap[(first_bit >> DMCP_META_BITS) + 1];
+		bits = DMCP_META_BITS - bits;
+		ret |= (data & ((1 << bits) - 1)) << (DMCP_META_BITS - bits);
+	}
+	return ret;
+}
+
+
+static void dm_icomp_mark_page(struct dm_icomp_info *info, u32 *addr,
+				bool dirty_meta)
+{
+	struct page *page;
+
+	page = vmalloc_to_page(addr);
+	if (!page)
+		return;
+	if (dirty_meta)
+		SetPageDirty(page);
+	else
+		ClearPageDirty(page);
+}
+
+/*
+ * set the meta data bits corresponding to a block
+ * @block_index : the index of the block
+ * @meta        : the meta data bits.
+ */
+static void dm_icomp_set_meta(struct dm_icomp_info *info, u64 block_index,
+		u8 meta, bool dirty_meta)
+{
+	u64 first_bit = block_index * DMCP_META_BITS;
+	int bits, offset;
+	u32 data;
+
+	offset = first_bit & (DMCP_BITS_PER_ENTRY-1);
+	bits = min_t(u32, DMCP_META_BITS, DMCP_BITS_PER_ENTRY - offset);
+
+
+	data = (u32)info->meta_bitmap[first_bit >> DMCP_META_BITS];
+	data &= ~(((1 << bits) - 1) << offset);
+	data |= (meta & ((1 << bits) - 1)) << offset;
+	info->meta_bitmap[first_bit >> DMCP_META_BITS] = (u32)data;
+
+	if (info->write_mode == DMCP_WRITE_BACK)
+		dm_icomp_mark_page(info,
+			&info->meta_bitmap[first_bit >> DMCP_META_BITS],
+			dirty_meta);
+
+	if (bits < DMCP_META_BITS) {
+		meta >>= bits;
+		data = (u32)
+			info->meta_bitmap[(first_bit >> DMCP_META_BITS) + 1];
+		bits = DMCP_META_BITS - bits;
+		data = (data >> bits) << bits;
+		data |= meta & ((1 << bits) - 1);
+		info->meta_bitmap[(first_bit >> DMCP_META_BITS) + 1] =
+				(u32)data;
+
+		if (info->write_mode == DMCP_WRITE_BACK)
+			dm_icomp_mark_page(info,
+			&info->meta_bitmap[(first_bit >> DMCP_META_BITS) + 1],
+			dirty_meta);
+	}
+}
+
+
+/*
+ * set the meta data bits corresponding to an extent
+ * @block : the index of the block
+ * @logical_blocks: the number of blocks in the extent
+ * @sectors: the number of sectors holding the compressed
+ *		data
+ */
+static void dm_icomp_set_extent(struct dm_icomp_req *req, u64 block,
+	u16 logical_blocks, sector_t data_sectors)
+{
+	int i;
+	u8 data;
+
+	for (i = 0; i < logical_blocks; i++) {
+		data = min_t(sector_t, data_sectors, 8);
+		data_sectors -= data;
+		if (i != 0)
+			data |= DMCP_TAIL_MASK;
+		/* For FUA, we write out meta data directly */
+		dm_icomp_set_meta(req->info, block + i, data,
+					!(req->bio->bi_opf & REQ_FUA));
+	}
+}
+
+/*
+ * get the meta data bits corresponding to an extent
+ * @block_index : the index of the block
+ * @logical_blocks: return the number of blocks in the extent
+ * @sectors: return the number of sectors holding the compressed
+ *		data
+ */
+static void dm_icomp_get_extent(struct dm_icomp_info *info, u64 block_index,
+	u64 *first_block_index, u16 *logical_sectors, u16 *data_sectors)
+{
+	u8 data;
+
+	data = dm_icomp_get_meta(info, block_index);
+	while (data & DMCP_TAIL_MASK) {
+		block_index--;
+		data = dm_icomp_get_meta(info, block_index);
+	}
+	*first_block_index = block_index;
+	*logical_sectors = DMCP_BYTES_TO_SECTOR(DMCP_BLOCK_SIZE);
+	*data_sectors = data & DMCP_LENGTH_MASK;
+	block_index++;
+	while (block_index < info->data_blocks) {
+		data = dm_icomp_get_meta(info, block_index);
+		if (!(data & DMCP_TAIL_MASK))
+			break;
+		*logical_sectors += DMCP_BYTES_TO_SECTOR(DMCP_BLOCK_SIZE);
+		*data_sectors += data & DMCP_LENGTH_MASK;
+		block_index++;
+	}
+}
+
+/*
+ * return the super block
+ */
+static int dm_icomp_access_super(struct dm_icomp_info *info, void *addr,
+		int op, int flag)
+{
+	struct dm_io_region region;
+	struct dm_io_request req;
+	unsigned long io_error = 0;
+	int ret;
+
+	region.bdev = info->dev->bdev;
+	region.sector = 0;
+	region.count = DMCP_BYTES_TO_SECTOR(DMCP_BLOCK_SIZE);
+
+	req.bi_op = op;
+	req.bi_op_flags = flag;
+	req.mem.type = DM_IO_KMEM;
+	req.mem.offset = 0;
+	req.mem.ptr.addr = addr;
+	req.notify.fn = NULL;
+	req.client = info->io_client;
+
+	ret = dm_io(&req, 1, &region, &io_error);
+	if (ret || io_error)
+		return -EIO;
+	return 0;
+}
+
+static void dm_icomp_meta_io_done(unsigned long error, void *context)
+{
+	struct dm_icomp_meta_io *meta_io = context;
+
+	meta_io->fn(meta_io->data, error);
+	kmem_cache_free(dm_icomp_meta_io_cachep, meta_io);
+}
+
+/*
+ * write meta data to the meta blocks in the backing store.
+ */
+static int dm_icomp_write_meta(struct dm_icomp_info *info, u64 start_page,
+	u64 end_page, void *data,
+	void (*fn)(void *data, unsigned long error), int rw, int flags)
+{
+	struct dm_icomp_meta_io *meta_io;
+	sector_t sector, last_sector, last_meta_sector = info->data_start-1;
+
+	WARN_ON(end_page > info->meta_bitmap_pages);
+
+	sector = DMCP_META_START_SECTOR + (start_page << (PAGE_SHIFT - 9));
+	WARN_ON(sector > last_meta_sector);
+	if (sector > last_meta_sector) {
+		fn(data, -EINVAL);
+		return -EINVAL;
+	}
+	last_sector = sector + ((end_page - start_page) << (PAGE_SHIFT - 9));
+	if (last_sector > last_meta_sector)
+		last_sector = last_meta_sector;
+
+
+	meta_io = kmem_cache_alloc(dm_icomp_meta_io_cachep, GFP_NOIO);
+	if (!meta_io) {
+		fn(data, -ENOMEM);
+		return -ENOMEM;
+	}
+	meta_io->data = data;
+	meta_io->fn = fn;
+
+	meta_io->io_region.bdev = info->dev->bdev;
+
+
+	meta_io->io_region.sector = sector;
+	meta_io->io_region.count = last_sector - sector + 1;
+	atomic64_add(DMCP_SECTOR_TO_BYTES(meta_io->io_region.count),
+				&info->meta_write_size);
+
+	meta_io->io_req.bi_op = rw;
+	meta_io->io_req.bi_op_flags = flags;
+	meta_io->io_req.mem.type = DM_IO_VMA;
+	meta_io->io_req.mem.offset = 0;
+	meta_io->io_req.mem.ptr.addr = ((char *)(info->meta_bitmap)) +
+						(start_page << PAGE_SHIFT);
+	meta_io->io_req.notify.fn = dm_icomp_meta_io_done;
+	meta_io->io_req.notify.context = meta_io;
+	meta_io->io_req.client = info->io_client;
+
+	dm_io(&meta_io->io_req, 1, &meta_io->io_region, NULL);
+	return 0;
+}
+
+struct writeback_flush_data {
+	struct completion complete;
+	atomic_t cnt;
+};
+
+static void writeback_flush_io_done(void *data, unsigned long error)
+{
+	struct writeback_flush_data *wb = data;
+
+	if (atomic_dec_return(&wb->cnt))
+		return;
+	complete(&wb->complete);
+}
+
+static void dm_icomp_flush_dirty_meta(struct dm_icomp_info *info,
+			struct writeback_flush_data *data)
+{
+	struct page *page;
+	u64 start = 0, index;
+	u32 pending = 0, cnt = 0;
+	bool dirty;
+	struct blk_plug plug;
+
+	blk_start_plug(&plug);
+	for (index = 0; index < info->meta_bitmap_pages; index++, cnt++) {
+		if (cnt == 256) {
+			cnt = 0;
+			cond_resched();
+		}
+
+		page = vmalloc_to_page((char *)(info->meta_bitmap) +
+					(index << PAGE_SHIFT));
+		if (!page)
+			DMWARN("Uable to find page for block=%llu", index);
+		dirty = TestClearPageDirty(page);
+
+		if (pending == 0 && dirty) {
+			start = index;
+			pending++;
+			continue;
+		} else if (pending == 0)
+			continue;
+		else if (pending > 0 && dirty) {
+			pending++;
+			continue;
+		}
+
+		/* pending > 0 && !dirty */
+		atomic_inc(&data->cnt);
+		dm_icomp_write_meta(info, start, start + pending, data,
+			writeback_flush_io_done, REQ_OP_WRITE, WRITE);
+		pending = 0;
+	}
+
+	if (pending > 0) {
+		atomic_inc(&data->cnt);
+		dm_icomp_write_meta(info, start, start + pending, data,
+			writeback_flush_io_done, REQ_OP_WRITE, WRITE);
+	}
+	blkdev_issue_flush(info->dev->bdev, GFP_NOIO, NULL);
+	blk_finish_plug(&plug);
+}
+
+static int dm_icomp_meta_writeback_thread(void *data)
+{
+	struct dm_icomp_info *info = data;
+	struct writeback_flush_data wb;
+
+	atomic_set(&wb.cnt, 1);
+	init_completion(&wb.complete);
+
+	while (!kthread_should_stop()) {
+		schedule_timeout_interruptible(
+			msecs_to_jiffies(info->writeback_delay * 1000));
+		dm_icomp_flush_dirty_meta(info, &wb);
+	}
+
+	dm_icomp_flush_dirty_meta(info, &wb);
+
+	writeback_flush_io_done(&wb, 0);
+	wait_for_completion(&wb.complete);
+	return 0;
+}
+
+static int dm_icomp_init_meta(struct dm_icomp_info *info, bool new)
+{
+	struct dm_io_region region;
+	struct dm_io_request req;
+	unsigned long io_error = 0;
+	struct blk_plug plug;
+	int ret;
+	ssize_t len = DIV_ROUND_UP_ULL(info->meta_bitmap_bits,
+			DMCP_BITS_PER_ENTRY);
+
+	len *= (DMCP_BITS_PER_ENTRY >> 3);
+
+	region.bdev = info->dev->bdev;
+	region.sector = DMCP_META_START_SECTOR;
+	region.count = DMCP_BYTES_TO_SECTOR(round_up(len,
+				DMCP_SECTOR_SIZE));
+
+	req.mem.type = DM_IO_VMA;
+	req.mem.offset = 0;
+	req.mem.ptr.addr = info->meta_bitmap;
+	req.notify.fn = NULL;
+	req.client = info->io_client;
+
+	blk_start_plug(&plug);
+	if (new) {
+		memset(info->meta_bitmap, 0, len);
+		req.bi_op = REQ_OP_WRITE;
+		req.bi_op_flags = REQ_FUA;
+		ret = dm_io(&req, 1, &region, &io_error);
+	} else {
+		req.bi_op = REQ_OP_READ;
+		req.bi_op_flags = READ;
+		ret = dm_io(&req, 1, &region, &io_error);
+	}
+	blk_finish_plug(&plug);
+
+	if (ret || io_error) {
+		info->ti->error = "Access metadata error";
+		return -EIO;
+	}
+
+	if (info->write_mode == DMCP_WRITE_BACK) {
+		info->writeback_tsk = kthread_run(
+			dm_icomp_meta_writeback_thread,
+			info, "dm_icomp_writeback");
+		if (!info->writeback_tsk) {
+			info->ti->error = "Create writeback thread error";
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+/***** END metadata logic *****/
+
+
+#define SET_REQ_STAGE(req, value) (req->stage = value)
+#define GET_REQ_STAGE(req) req->stage
+
+
+static void print_max_sectors_possible(struct dm_icomp_info *info)
+{
+	u64 total_blocks, data_blocks, meta_blocks;
+	u64 no_pairs;
+	u32 pair_blocks, rem;
+
+	/* superblock takes away one block */
+	total_blocks = DMCP_BYTES_TO_BLOCK(i_size_read(
+				info->dev->bdev->bd_inode)) - 1;
+
+	/* number of datablocks representable by one metadata block. */
+	data_blocks  = DIV_ROUND_CLOSEST_ULL((DMCP_BLOCK_SIZE * 8),
+			 DMCP_META_BITS);
+	meta_blocks  = 1; /* we need this one meta data block for sure. */
+
+
+	/* how many such pairing can we make ? */
+	pair_blocks  = data_blocks + meta_blocks;
+	no_pairs     = DIV_ROUND_CLOSEST_ULL(total_blocks, pair_blocks);
+
+
+	/*
+	 * these many datablocks and these many ..
+	 * metadatablocks will support each other.
+	 */
+	data_blocks  *= no_pairs;
+	meta_blocks  *= no_pairs;
+
+	div_u64_rem(total_blocks, pair_blocks, &rem);
+	if (rem) {
+		/* we have some remaining blocks.
+		 * give one to meta and remaining to data.
+		 */
+		meta_blocks++;
+		data_blocks += (rem - 1);
+	}
+
+	DMINFO(" This device can accommodate at most %llu sector ",
+		DMCP_BLOCK_TO_SECTOR(data_blocks));
+}
+
+
+/*
+ * create a new super block and initialize its contents.
+ */
+static int dm_icomp_read_or_create_super(struct dm_icomp_info *info)
+{
+	void *addr, *bitmap_addr;
+	struct dm_icomp_super_block *super;
+	u64 total_blocks, data_blocks, meta_blocks;
+	bool new_super = false;
+	int ret;
+	ssize_t len;
+
+	info->total_sector = DMCP_BYTES_TO_SECTOR(
+			i_size_read(info->dev->bdev->bd_inode));
+	total_blocks = DMCP_SECTOR_TO_BLOCK(info->total_sector) - 1;
+
+	data_blocks =  DMCP_SECTOR_TO_BLOCK(info->ti->len);
+	meta_blocks =  ((data_blocks * DMCP_META_BITS) +
+			((DMCP_BLOCK_SIZE * 8) - 1)) / (DMCP_BLOCK_SIZE * 8);
+
+	info->data_blocks = data_blocks;
+	info->data_start = DMCP_BLOCK_TO_SECTOR(1 + meta_blocks);
+
+	DMINFO(
+	"data_start=%u data_blocks=%llu metablocks=%llu total_blocks=%llu",
+		(unsigned int)info->data_start, info->data_blocks,
+		meta_blocks, total_blocks);
+
+	if (DMCP_BLOCK_TO_SECTOR(data_blocks + meta_blocks + 1)
+			>= info->total_sector) {
+		print_max_sectors_possible(info);
+		info->ti->error =
+			"Insufficient sectors to satisfy requested size";
+		return -ENOMEM;
+	}
+
+	addr = kzalloc(DMCP_BLOCK_SIZE+DMCP_SECTOR_SIZE, GFP_KERNEL);
+	if (!addr) {
+		info->ti->error = "Cannot allocate super";
+		return -ENOMEM;
+	}
+
+	super = PTR_ALIGN(addr, DMCP_SECTOR_SIZE);
+	ret = dm_icomp_access_super(info, super, REQ_OP_READ, REQ_FUA);
+	if (ret)
+		goto out;
+
+	if (le64_to_cpu(super->magic) == DMCP_SUPER_MAGIC) {
+
+		const char *alg_name;
+
+		if (le64_to_cpu(super->meta_blocks) != meta_blocks ||
+		    le64_to_cpu(super->data_blocks) != data_blocks) {
+			info->ti->error = "Super is invalid";
+			ret = -EINVAL;
+			goto out;
+		}
+
+		alg_name = get_comp_name(super->comp_alg);
+		if (!crypto_has_comp(alg_name, 0, 0)) {
+			info->ti->error =
+				"Compressor algorithm doesn't support";
+			ret = -EINVAL;
+			goto out;
+		}
+		info->comp_alg = super->comp_alg;
+
+	} else {
+		super->magic = cpu_to_le64(DMCP_SUPER_MAGIC);
+		super->meta_blocks = cpu_to_le64(meta_blocks);
+		super->data_blocks = cpu_to_le64(data_blocks);
+		super->comp_alg = info->comp_alg;
+		ret = dm_icomp_access_super(info, super, REQ_OP_WRITE,
+				REQ_FUA);
+		if (ret) {
+			info->ti->error = "Access super fails";
+			goto out;
+		}
+		new_super = true;
+	}
+
+	if (alloc_compressor(info)) {
+		info->ti->error = "Cannot allocate compressor";
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	info->meta_bitmap_bits = data_blocks * DMCP_META_BITS;
+	len = DIV_ROUND_UP_ULL(info->meta_bitmap_bits, DMCP_BITS_PER_ENTRY);
+	len *= (DMCP_BITS_PER_ENTRY >> 3);
+	info->meta_bitmap_pages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	bitmap_addr = vzalloc((info->meta_bitmap_pages * PAGE_SIZE) +
+				DMCP_SECTOR_SIZE);
+	if (!bitmap_addr) {
+		info->ti->error = "Cannot allocate bitmap";
+		ret = -ENOMEM;
+		goto bitmap_err;
+	}
+	info->meta_bitmap = PTR_ALIGN(bitmap_addr, DMCP_SECTOR_SIZE);
+
+	ret = dm_icomp_init_meta(info, new_super);
+	if (ret)
+		goto meta_err;
+
+	return 0;
+meta_err:
+	vfree(bitmap_addr);
+bitmap_err:
+	free_compressor(info);
+out:
+	kfree(addr);
+	return ret;
+}
+
+/*
+ * <dev> [ <writethough>/<writeback> <meta_commit_delay> ]
+ *	 [ <compressor> <type> ]
+ */
+static int dm_icomp_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+	struct dm_icomp_info *info;
+	char mode[15];
+	int par = 0;
+	int ret, i;
+
+	info = kzalloc(sizeof(*info), GFP_KERNEL);
+	if (!info) {
+		ti->error = "dm-inplace-compress: Cannot allocate context";
+		return -ENOMEM;
+	}
+	info->ti = ti;
+	info->comp_alg = get_default_compressor();
+	info->critical = false;
+	while (++par < argc) {
+		if (sscanf(argv[par], "%s", mode) != 1) {
+			ti->error = "Invalid argument";
+			ret = -EINVAL;
+			goto err_para;
+		}
+
+		if (strcmp(mode, "writeback") == 0) {
+			info->write_mode = DMCP_WRITE_BACK;
+			if (kstrtouint(argv[++par], 10,
+				 &info->writeback_delay)) {
+				ti->error = "Invalid argument";
+				ret = -EINVAL;
+				goto err_para;
+			}
+		} else if (strcmp(mode, "writethrough") == 0) {
+			info->write_mode = DMCP_WRITE_THROUGH;
+		} else if (strcmp(mode, "critical") == 0) {
+			info->critical = true;
+		} else if (strcmp(mode, "compressor") == 0) {
+			if (sscanf(argv[++par], "%s", mode) != 1) {
+				ti->error = "Invalid argument";
+				ret = -EINVAL;
+				goto err_para;
+			}
+			ret = get_comp_id(mode);
+			if (ret >= 0) {
+				DMINFO("compressor  is %s", mode);
+				info->comp_alg = ret;
+			} else {
+				ti->error = "Unsupported compressor";
+				ret = -EINVAL;
+				goto err_para;
+			}
+		}
+	}
+
+	if (dm_get_device(ti, argv[0], dm_table_get_mode(ti->table),
+							&info->dev)) {
+		ti->error = "Can't get device";
+		ret = -EINVAL;
+		goto err_para;
+	}
+
+	info->io_client = dm_io_client_create();
+	if (!info->io_client) {
+		ti->error = "Can't create io client";
+		ret = -EINVAL;
+		goto err_ioclient;
+	}
+
+	if (bdev_logical_block_size(info->dev->bdev) != 512) {
+		ti->error = "Can't logical block size too big";
+		ret = -EINVAL;
+		goto err_blocksize;
+	}
+
+	if (dm_set_target_max_io_len(ti, DMCP_BYTES_TO_SECTOR(DMCP_MAX_SIZE))) {
+		ti->error = "Failed to configure device ";
+		ret = -EINVAL;
+		goto err_blocksize;
+	}
+
+	if (dm_icomp_read_or_create_super(info)) {
+		ret = -EINVAL;
+		goto err_blocksize;
+	}
+
+	for (i = 0; i < BITMAP_HASH_LEN; i++) {
+		info->bitmap_locks[i].io_running = 0;
+		spin_lock_init(&info->bitmap_locks[i].wait_lock);
+		INIT_LIST_HEAD(&info->bitmap_locks[i].wait_list);
+	}
+
+	atomic64_set(&info->compressed_write_size, 0);
+	atomic64_set(&info->uncompressed_write_size, 0);
+	atomic64_set(&info->meta_write_size, 0);
+	atomic64_set(&dm_icomp_total_alloc_size, 0);
+	atomic64_set(&dm_icomp_total_bio_save, 0);
+
+	ti->num_flush_bios = 1;
+	ti->private = info;
+	return 0;
+
+err_blocksize:
+	dm_io_client_destroy(info->io_client);
+err_ioclient:
+	dm_put_device(ti, info->dev);
+err_para:
+	kfree(info);
+	return ret;
+}
+
+static void dm_icomp_dtr(struct dm_target *ti)
+{
+	struct dm_icomp_info *info = ti->private;
+
+	if (info->write_mode == DMCP_WRITE_BACK)
+		kthread_stop(info->writeback_tsk);
+	free_compressor(info);
+	vfree(info->meta_bitmap);
+	dm_io_client_destroy(info->io_client);
+	dm_put_device(ti, info->dev);
+	kfree(info);
+}
+
+/*
+ * return the range lock to this block.
+ */
+static struct dm_icomp_hash_lock *dm_icomp_block_hash_lock(
+		struct dm_icomp_info *info, u64 block_index)
+{
+	return &info->bitmap_locks[(block_index >> BITMAP_HASH_SHIFT) &
+			BITMAP_HASH_MASK];
+}
+
+/*
+ * unlock the io range correspondingg to this block.
+ */
+static struct dm_icomp_hash_lock *dm_icomp_trylock_block(
+		struct dm_icomp_info *info,
+		struct dm_icomp_req *req, u64 block_index)
+{
+	struct dm_icomp_hash_lock *hash_lock;
+
+	hash_lock = dm_icomp_block_hash_lock(req->info, block_index);
+
+	spin_lock_irq(&hash_lock->wait_lock);
+	if (!hash_lock->io_running) {
+		hash_lock->io_running = 1;
+		spin_unlock_irq(&hash_lock->wait_lock);
+		return hash_lock;
+	}
+	list_add_tail(&req->sibling, &hash_lock->wait_list);
+	spin_unlock_irq(&hash_lock->wait_lock);
+	return NULL;
+}
+
+static void dm_icomp_queue_req_list(struct dm_icomp_info *info,
+	 struct list_head *list);
+
+static void dm_icomp_unlock_block(struct dm_icomp_info *info,
+	struct dm_icomp_req *req, struct dm_icomp_hash_lock *hash_lock)
+{
+	LIST_HEAD(pending_list);
+	unsigned long flags;
+
+	spin_lock_irqsave(&hash_lock->wait_lock, flags);
+	/* wakeup all pending reqs to avoid live lock */
+	list_splice_init(&hash_lock->wait_list, &pending_list);
+	hash_lock->io_running = 0;
+	spin_unlock_irqrestore(&hash_lock->wait_lock, flags);
+
+	dm_icomp_queue_req_list(info, &pending_list);
+}
+
+/*
+ * lock all the range locks corresponding to this io request.
+ */
+static int dm_icomp_lock_req_range(struct dm_icomp_req *req)
+{
+	u64 block_index, first_block_index;
+	u64 first_lock_block, second_lock_block;
+	u16 logical_sectors, data_sectors;
+
+	block_index = DMCP_SECTOR_TO_BLOCK(req->bio->bi_iter.bi_sector);
+	req->locks[0] = dm_icomp_trylock_block(req->info, req, block_index);
+	if (!req->locks[0])
+		return 0;
+	dm_icomp_get_extent(req->info, block_index, &first_block_index,
+				&logical_sectors, &data_sectors);
+	if (dm_icomp_block_hash_lock(req->info, first_block_index) !=
+						req->locks[0]) {
+		dm_icomp_unlock_block(req->info, req, req->locks[0]);
+		first_lock_block = first_block_index;
+		second_lock_block = block_index;
+		goto two_locks;
+	}
+
+	block_index = DMCP_SECTOR_TO_BLOCK(bio_end_sector(req->bio) - 1);
+	dm_icomp_get_extent(req->info, block_index, &first_block_index,
+				&logical_sectors, &data_sectors);
+	first_block_index += DMCP_SECTOR_TO_BLOCK(logical_sectors);
+	if (dm_icomp_block_hash_lock(req->info, first_block_index) !=
+						req->locks[0]) {
+		second_lock_block = first_block_index;
+		goto second_lock;
+	}
+	req->locked_locks = 1;
+	return 1;
+
+two_locks:
+	req->locks[0] = dm_icomp_trylock_block(req->info, req,
+		first_lock_block);
+	if (!req->locks[0])
+		return 0;
+second_lock:
+	req->locks[1] = dm_icomp_trylock_block(req->info, req,
+				second_lock_block);
+	if (!req->locks[1]) {
+		dm_icomp_unlock_block(req->info, req, req->locks[0]);
+		return 0;
+	}
+	/* Don't need check if meta is changed */
+	req->locked_locks = 2;
+	return 1;
+}
+
+
+
+/*
+ * unlock all the range locks corresponding to this io request.
+ */
+static void dm_icomp_unlock_req_range(struct dm_icomp_req *req)
+{
+	int i;
+
+	for (i = req->locked_locks - 1; i >= 0; i--)
+		dm_icomp_unlock_block(req->info, req, req->locks[i]);
+}
+
+static void dm_icomp_queue_req(struct dm_icomp_info *info,
+		struct dm_icomp_req *req)
+{
+	unsigned long flags;
+	struct dm_icomp_io_worker *worker = &dm_icomp_io_workers[req->cpu];
+
+	spin_lock_irqsave(&worker->lock, flags);
+	list_add_tail(&req->sibling, &worker->pending);
+	spin_unlock_irqrestore(&worker->lock, flags);
+
+	queue_work_on(req->cpu, dm_icomp_wq, &worker->work);
+}
+
+static void dm_icomp_queue_req_list(struct dm_icomp_info *info,
+		struct list_head *list)
+{
+	struct dm_icomp_req *req;
+
+	while (!list_empty(list)) {
+		req = list_first_entry(list, struct dm_icomp_req, sibling);
+		list_del_init(&req->sibling);
+		dm_icomp_queue_req(info, req);
+	}
+}
+
+static void dm_icomp_get_req(struct dm_icomp_req *req)
+{
+	atomic_inc(&req->io_pending);
+}
+
+static inline int get_alloc_flag(struct dm_icomp_info *info)
+{
+	/*
+	 * Use GFP_ATOMIC allocations if the device
+	 * is used on the critical path
+	 */
+	return info->critical ? GFP_ATOMIC : GFP_NOIO;
+}
+
+static void *dm_icomp_kmalloc(size_t size, int alloc_flag)
+{
+	void *addr = kmalloc(size, alloc_flag);
+
+	if (!addr)
+		return NULL;
+	DMCP_ALLOC(size);
+	return addr;
+}
+
+static void *dm_icomp_krealloc(void *ptr, size_t size,
+		size_t origsize, int alloc_flag)
+{
+	void *addr = krealloc(ptr, size, alloc_flag);
+
+	if (!addr)
+		return NULL;
+	DMCP_FREE_ALLOC(origsize);
+	DMCP_ALLOC(size);
+	return addr;
+}
+
+static int dm_icomp_alloc_compbuffer(struct dm_icomp_io_range *io, int size)
+{
+	int alloc_len = size + DMCP_SECTOR_SIZE;
+	void *addr = dm_icomp_kmalloc(alloc_len,
+			get_alloc_flag(io->req->info));
+
+	if (!addr)
+		return 1;
+
+	io->comp_real_data = addr;
+	io->comp_kmap	= false;
+	io->comp_len	= size;
+
+	/*
+	 * comp_data is used to read and write from storage.
+	 * So align it.
+	 */
+	io->comp_data   = io->io_req.mem.ptr.addr
+			= PTR_ALIGN(addr, DMCP_SECTOR_SIZE);
+
+	return 0;
+}
+
+static int dm_icomp_realloc_compbuffer(struct dm_icomp_io_range *io, int size)
+{
+	void *addr = dm_icomp_krealloc(io->comp_real_data,
+			size+DMCP_SECTOR_SIZE, io->comp_len,
+				get_alloc_flag(io->req->info));
+	if (!addr)
+		return 1;
+
+	io->comp_real_data = addr;
+	io->comp_kmap	   = false;
+	io->comp_data      = io->io_req.mem.ptr.addr = PTR_ALIGN(addr,
+				DMCP_SECTOR_SIZE);
+	io->comp_len	   = size;
+	return 0;
+}
+
+static void dm_icomp_kfree(void *addr, unsigned int size)
+{
+	kfree(addr);
+	DMCP_FREE_ALLOC(size);
+}
+
+static void dm_icomp_release_decomp_buffer(struct dm_icomp_io_range *io)
+{
+	if (!io->decomp_data)
+		return;
+
+	if (io->decomp_kmap)
+		kunmap(io->decomp_real_data);
+	else
+		dm_icomp_kfree(io->decomp_real_data, io->decomp_len);
+
+	io->decomp_data = io->decomp_real_data = NULL;
+	io->decomp_len  = 0;
+	io->decomp_kmap = false;
+}
+
+static void dm_icomp_release_comp_buffer(struct dm_icomp_io_range *io)
+{
+	if (!io->comp_data)
+		return;
+
+	if (io->comp_kmap)
+		kunmap(io->comp_real_data);
+	else
+		dm_icomp_kfree(io->comp_real_data, io->comp_len);
+
+	io->comp_real_data = io->comp_data = NULL;
+	io->comp_len = 0;
+	io->comp_kmap = false;
+}
+
+static void dm_icomp_free_io_range(struct dm_icomp_io_range *io)
+{
+	dm_icomp_release_decomp_buffer(io);
+	dm_icomp_release_comp_buffer(io);
+	kmem_cache_free(dm_icomp_io_range_cachep, io);
+}
+
+static void dm_icomp_put_req(struct dm_icomp_req *req)
+{
+	struct dm_icomp_io_range *io;
+
+	if (atomic_dec_return(&req->io_pending))
+		return;
+
+	if (GET_REQ_STAGE(req) == STAGE_INIT) /* waiting for locking */
+		return;
+
+	if (GET_REQ_STAGE(req) == STAGE_READ_DECOMP ||
+	    GET_REQ_STAGE(req) == STAGE_WRITE_COMP)
+		SET_REQ_STAGE(req, STAGE_DONE);
+
+	if (!!!req->result && GET_REQ_STAGE(req) != STAGE_DONE) {
+		dm_icomp_queue_req(req->info, req);
+		return;
+	}
+
+	while (!list_empty(&req->all_io)) {
+		io = list_entry(req->all_io.next,
+			struct dm_icomp_io_range, next);
+		list_del(&io->next);
+		dm_icomp_free_io_range(io);
+	}
+
+	dm_icomp_unlock_req_range(req);
+
+	req->bio->bi_error = req->result;
+
+	bio_endio(req->bio);
+	kmem_cache_free(dm_icomp_req_cachep, req);
+}
+
+static void dm_icomp_bio_copy(struct bio *bio, off_t bio_off, void *buf,
+		ssize_t len, bool to_buf)
+{
+	struct bio_vec bv;
+	struct bvec_iter iter;
+	off_t buf_off = 0;
+	ssize_t size;
+	void *addr;
+
+	WARN_ON(bio_off + len > DMCP_SECTOR_TO_BYTES(bio_sectors(bio)));
+
+	bio_for_each_segment(bv, bio, iter) {
+		int length = bv.bv_len;
+
+		if (bio_off > length) {
+			bio_off -= length;
+			continue;
+		}
+		addr = kmap_atomic(bv.bv_page);
+		size = min_t(ssize_t, len, length - bio_off);
+		if (!buf)
+			memset(addr + bio_off + bv.bv_offset, 0, size);
+		else if (to_buf)
+			memcpy(buf + buf_off, addr + bio_off + bv.bv_offset,
+				size);
+		else
+			memcpy(addr + bio_off + bv.bv_offset, buf + buf_off,
+				size);
+		kunmap_atomic(addr);
+		bio_off = 0;
+		buf_off += size;
+
+		if (len <= size)
+			break;
+
+		len -= size;
+	}
+}
+
+static void dm_icomp_io_range_done(unsigned long error, void *context)
+{
+	struct dm_icomp_io_range *io = context;
+
+	if (error)
+		io->req->result = error;
+
+	dm_icomp_put_req(io->req);
+}
+
+static inline int dm_icomp_compressor_len(struct dm_icomp_info *info, int len)
+{
+	if (compressors[info->comp_alg].comp_len)
+		return compressors[info->comp_alg].comp_len(len);
+	return len;
+}
+
+static inline bool dm_icomp_can_handle_overflow(struct dm_icomp_info *info)
+{
+	return compressors[info->comp_alg].can_handle_overflow;
+}
+
+static inline int dm_icomp_compressor_maxlen(struct dm_icomp_info *info,
+		int len)
+{
+	if (compressors[info->comp_alg].max_comp_len)
+		return compressors[info->comp_alg].max_comp_len(len);
+	return len;
+}
+
+/*
+ * caller should set region.sector, region.count. bi_rw. IO always to/from
+ * comp_data
+ */
+static struct dm_icomp_io_range *dm_icomp_create_io_range(
+		struct dm_icomp_req *req)
+{
+	struct dm_icomp_io_range *io;
+
+	io = kmem_cache_alloc(dm_icomp_io_range_cachep, GFP_NOIO);
+	if (!io)
+		return NULL;
+
+	io->io_req.notify.fn = dm_icomp_io_range_done;
+	io->io_req.notify.context = io;
+	io->io_req.client = req->info->io_client;
+	io->io_req.mem.type = DM_IO_KMEM;
+	io->io_req.mem.offset = 0;
+
+	io->io_region.bdev = req->info->dev->bdev;
+	io->req = req;
+
+	io->comp_data = io->comp_real_data =
+			io->decomp_data = io->decomp_real_data = NULL;
+
+	io->data_bytes = io->comp_len =
+			io->decomp_len = io->logical_bytes = 0;
+
+	io->comp_kmap = io->decomp_kmap = false;
+	return io;
+}
+
+
+/*
+ * return an address, within the bio. The address corresponds to
+ * the requested offset 'bio_off' and is contiguous of size 'len'
+ */
+static void *get_addr(struct bio *bio,  int len, u64 bio_off, u64 *offset)
+{
+	struct bio_vec bv;
+	struct bvec_iter iter;
+	void *addr;
+
+	bio_for_each_segment(bv, bio, iter) {
+		int length = bv.bv_len;
+
+		if (bio_off > length) {
+			bio_off -= length;
+			continue;
+		}
+		addr = bv.bv_page;
+		if (bv.bv_offset + bio_off + len >= length) {
+			*offset = bv.bv_offset + bio_off;
+			return kmap(addr);
+		}
+		break;
+	}
+	return NULL;
+}
+
+
+/*
+ * create a io range for tracking  predominantly a read request.
+ * @req		: the read request
+ * @comp_len	: allocation size of the compress buffer
+ * @decomp_len	: allocation size of the decompress buffer
+ * @actual_comp_len : real size of the compress data
+ * @bio_off	: offset within the bio read buffer this request corresponds to.
+ *		try to reuse and read into the bio buffer. -1 means don't reuse.
+ */
+static struct dm_icomp_io_range *dm_icomp_create_io_read_range(
+		struct dm_icomp_req *req, int comp_len, int decomp_len,
+		long bio_off, int actual_comp_len)
+{
+	struct bio *bio = req->bio;
+	void *addr = NULL;
+	struct dm_icomp_io_range *io = dm_icomp_create_io_range(req);
+	u64 offset;
+
+	if (!io)
+		return NULL;
+
+	WARN_ON(comp_len % DMCP_SECTOR_SIZE);
+
+	/* try reusing the bio if possible */
+	if (bio_off >= 0) {
+		addr = get_addr(bio, comp_len, (u64)bio_off, &offset);
+		if (addr) {
+			io->comp_real_data =  addr;
+			io->comp_data = io->io_req.mem.ptr.addr = addr + offset;
+			io->comp_kmap = true;
+			io->comp_len  = comp_len;
+		}
+	}
+
+	if (!addr && dm_icomp_alloc_compbuffer(io, comp_len)) {
+		kmem_cache_free(dm_icomp_io_range_cachep, io);
+		return NULL;
+	}
+
+	io->data_bytes	= actual_comp_len;  /* NOTE, this value can change */
+
+	/*
+	 * note requested length for decompress buffer. Do not allocate it yet.
+	 * Value once set is final.
+	 */
+	io->logical_bytes = decomp_len;
+
+	return io;
+}
+
+/*
+ *  ensure that the io range has all its buffers; of the correct size,
+ *  allocated.
+ */
+static int dm_icomp_update_io_read_range(struct dm_icomp_io_range *io)
+{
+	WARN_ON(!io->comp_data);
+	WARN_ON(io->decomp_data || io->decomp_len);
+	io->decomp_data = dm_icomp_kmalloc(io->logical_bytes,
+				get_alloc_flag(io->req->info));
+	if (!io->decomp_data)
+		return 1;
+	io->decomp_real_data = io->decomp_data;
+	io->decomp_len = io->logical_bytes;
+	io->decomp_kmap = false;
+	return 0;
+}
+
+/*
+ *  resize the comp buffer to its largest possible size.
+ */
+static int dm_icomp_mod_to_max_io_range(struct dm_icomp_info *info,
+			 struct dm_icomp_io_range *io)
+{
+	unsigned int maxlen = dm_icomp_compressor_maxlen(info, io->decomp_len);
+
+	WARN_ON(maxlen > io->logical_bytes);
+
+	if (io->comp_kmap) {
+		WARN_ON(io->comp_kmap);
+		kunmap(io->comp_real_data);
+		io->comp_kmap = false;
+		io->comp_real_data = io->comp_data = NULL;
+	}
+
+	if (dm_icomp_realloc_compbuffer(io, maxlen)) {
+		io->comp_len = 0;
+		return -ENOSPC;
+	}
+	io->comp_len = maxlen;
+	return 0;
+}
+
+/*
+ * create a io range for tracking a write request.
+ * @req		: the write request
+ * @count	: size of the write in sectors.
+ * @offset	: offset within the bio read buffer this request correspond to.
+ */
+static struct dm_icomp_io_range *dm_icomp_create_io_write_range(
+	struct dm_icomp_req *req, sector_t offset, sector_t count)
+{
+	struct bio *bio = req->bio;
+	int size  = DMCP_SECTOR_TO_BYTES(count);
+	u64 of;
+	int comp_len = dm_icomp_compressor_len(req->info, size);
+	void *addr;
+	struct dm_icomp_io_range *io = dm_icomp_create_io_range(req);
+
+	if (!io)
+		return NULL;
+
+	WARN_ON(io->comp_data);
+
+	if (dm_icomp_alloc_compbuffer(io, comp_len)) {
+		kmem_cache_free(dm_icomp_io_range_cachep, io);
+		return NULL;
+	}
+
+	/* we donot know the size of the compress segment yet. */
+	io->data_bytes = 0;
+
+
+	WARN_ON(io->decomp_data);
+
+	io->decomp_kmap = false;
+
+	/* try reusing the bio buffer for decomp data. */
+	addr = get_addr(bio, size, DMCP_SECTOR_TO_BYTES(offset), &of);
+	if (addr)
+		io->decomp_kmap = true;
+	else
+		addr  = dm_icomp_kmalloc(size,
+				get_alloc_flag(req->info));
+
+	if (!addr) {
+		dm_icomp_kfree(io->comp_data, comp_len);
+		kmem_cache_free(dm_icomp_io_range_cachep, io);
+		return NULL;
+	}
+
+	io->logical_bytes = io->decomp_len = size;
+
+	if (io->decomp_kmap) {
+		io->decomp_real_data = addr;
+		io->decomp_data = addr + of;
+		DMCP_ALLOC_SAVE(size);
+	} else {
+		io->decomp_data = io->decomp_real_data = addr;
+		dm_icomp_bio_copy(req->bio, DMCP_SECTOR_TO_BYTES(offset),
+			io->decomp_data, size, true);
+	}
+
+	return io;
+}
+
+static unsigned int round_to_next_sector(unsigned int val)
+{
+	unsigned int c = round_up(val, DMCP_SECTOR_SIZE);
+
+	if ((c - val) < 2*sizeof(u32))
+		c += DMCP_SECTOR_SIZE;
+	return c;
+}
+
+/*
+ * compress and store the data in compress buffer.
+ * return value:
+ * < 0 : error
+ * == 0 : ok
+ * == 1 : ok, but comp/decomp is skipped
+ * Compressed data size is roundup of 512, which makes the payload.
+ * We store the actual compressed len in the last u32 of the payload.
+ * If there is no free space, we add 512 to the payload size.
+ */
+static int dm_icomp_io_range_compress(struct dm_icomp_info *info,
+		struct dm_icomp_io_range *io, unsigned int *comp_len)
+{
+	unsigned int actual_comp_len = io->comp_len;
+	u32 *addr;
+	struct crypto_comp *tfm =  info->tfm[get_cpu()];
+	unsigned int decomp_len = io->logical_bytes;
+	int ret;
+
+	actual_comp_len = io->comp_len;
+	ret = crypto_comp_compress(tfm, io->decomp_data, decomp_len,
+		io->comp_data, &actual_comp_len);
+
+	if (ret || round_to_next_sector(actual_comp_len) > io->comp_len) {
+		ret = dm_icomp_mod_to_max_io_range(info, io);
+		if (!ret) {
+			actual_comp_len = io->comp_len;
+			ret = crypto_comp_compress(tfm, io->decomp_data,
+				decomp_len, io->comp_data,
+				&actual_comp_len);
+		}
+	}
+
+	put_cpu();
+
+	atomic64_add(decomp_len, &info->uncompressed_write_size);
+	io->data_bytes = *comp_len = round_to_next_sector(actual_comp_len);
+	if (ret || decomp_len < *comp_len) {
+		*comp_len = decomp_len;
+		memcpy(io->comp_data, io->decomp_data, *comp_len);
+		atomic64_add(*comp_len, &info->compressed_write_size);
+	} else {
+		atomic64_add(*comp_len, &info->compressed_write_size);
+		addr = (u32 *)((char *)io->comp_data + *comp_len);
+		addr--;
+		*addr = cpu_to_le32(actual_comp_len);
+		addr--;
+		*addr = cpu_to_le32(DMCP_COMPRESS_MAGIC);
+	}
+
+	return 0;
+}
+
+/*
+ * decompress and store the data in decompress buffer.
+ * return value:
+ * < 0 : error
+ * == 0 : ok
+ */
+static int dm_icomp_io_range_decompress(struct dm_icomp_info *info,
+		struct dm_icomp_io_range *io, unsigned int *decomp_len)
+{
+	struct crypto_comp *tfm;
+	u32 *addr;
+	int ret;
+	int comp_len = io->data_bytes;
+
+	WARN_ON(!io->data_bytes);
+
+	if (comp_len == io->logical_bytes) {
+		memcpy(io->decomp_data, io->comp_data, comp_len);
+		*decomp_len = comp_len;
+		return 0;
+	}
+
+	WARN_ON(io->comp_data != io->io_req.mem.ptr.addr);
+
+	addr = (u32 *)((char *)(io->comp_data) + comp_len);
+	addr--;
+	comp_len = le32_to_cpu(*addr);
+	addr--;
+
+	if (le32_to_cpu(*addr) == DMCP_COMPRESS_MAGIC) {
+		tfm = info->tfm[get_cpu()];
+		*decomp_len = io->logical_bytes;
+		ret = crypto_comp_decompress(tfm, io->comp_data, comp_len,
+			io->decomp_data, decomp_len);
+		WARN_ON(*decomp_len != io->decomp_len);
+		put_cpu();
+		if (ret)
+			return -EINVAL;
+		return 0;
+	}
+
+	DMWARN("Decompress Error ");
+	return -1;
+}
+
+/*
+ *  fill the bio with the corresponding decompressed data.
+ */
+static void dm_icomp_handle_read_decomp(struct dm_icomp_req *req)
+{
+	struct dm_icomp_io_range *io;
+	off_t bio_off = 0;
+	int ret;
+	sector_t bio_len  = DMCP_SECTOR_TO_BYTES(bio_sectors(req->bio));
+
+	SET_REQ_STAGE(req, STAGE_READ_DECOMP);
+
+	if (req->result)
+		return;
+
+	list_for_each_entry(io, &req->all_io, next) {
+		ssize_t dst_off = 0, src_off = 0, len;
+		unsigned int decomp_len;
+
+		io->io_region.sector -= req->info->data_start;
+
+		if (io->io_region.sector >=
+				req->bio->bi_iter.bi_sector)
+			dst_off = DMCP_SECTOR_TO_BYTES(
+				io->io_region.sector -
+				req->bio->bi_iter.bi_sector);
+		else
+			src_off = DMCP_SECTOR_TO_BYTES(
+				req->bio->bi_iter.bi_sector -
+				io->io_region.sector);
+
+		if (dm_icomp_update_io_read_range(io)) {
+			req->result = -EIO;
+			return;
+		}
+
+		/* Do decomp here */
+		ret = dm_icomp_io_range_decompress(req->info, io, &decomp_len);
+		if (ret < 0) {
+			dm_icomp_release_decomp_buffer(io);
+			dm_icomp_release_comp_buffer(io);
+			req->result = -EIO;
+			return;
+		}
+
+		len = min_t(ssize_t,
+			max_t(ssize_t, decomp_len - src_off, 0),
+			max_t(ssize_t, bio_len - dst_off, 0));
+
+		dm_icomp_bio_copy(req->bio, dst_off,
+			   io->decomp_data + src_off, len, false);
+
+		/* io range in all_io list is ordered for read IO */
+		while (bio_off < dst_off) {
+			ssize_t size = min_t(ssize_t, PAGE_SIZE,
+					dst_off - bio_off);
+			dm_icomp_bio_copy(req->bio, bio_off, NULL,
+					size, false);
+			bio_off += size;
+		}
+
+		bio_off = dst_off + len;
+		dm_icomp_release_decomp_buffer(io);
+		dm_icomp_release_comp_buffer(io);
+	}
+
+	while (bio_off < bio_len) {
+		ssize_t size = min_t(ssize_t, PAGE_SIZE, (bio_len - bio_off));
+
+		dm_icomp_bio_copy(req->bio, bio_off, NULL,
+			size, false);
+		bio_off += size;
+	}
+}
+
+
+/*
+ * read an extent
+ * @req        : the read request
+ * @block      : the block to be read
+ * @logical_sectors   : no of sectors occupied by the decompressed data
+ * @data_sectors      : no of sectors occupied by the compressed data
+ * @may_resize : the compress data size may change during its life.
+ */
+static void dm_icomp_read_one_extent(struct dm_icomp_req *req, u64 block,
+	u16 logical_sectors, u16 data_sectors, bool may_resize)
+{
+	struct dm_icomp_io_range *io;
+	long bio_off = 0, comp_len;
+	int actual_comp_len = DMCP_SECTOR_TO_BYTES(data_sectors);
+	int actual_decomp_len = DMCP_SECTOR_TO_BYTES(logical_sectors);
+
+	comp_len = actual_comp_len;
+	if (may_resize && !dm_icomp_can_handle_overflow(req->info))
+		comp_len = dm_icomp_compressor_maxlen(req->info,
+				actual_decomp_len);
+
+	bio_off	 =  (may_resize) ? -1 :
+			 DMCP_BLOCK_TO_SECTOR(block) -
+				req->bio->bi_iter.bi_sector;
+
+	io = dm_icomp_create_io_read_range(req, comp_len,
+		actual_decomp_len,
+		bio_off,
+		actual_comp_len);
+	if (!io) {
+		req->result = -EIO;
+		return;
+	}
+
+	dm_icomp_get_req(req);
+	list_add_tail(&io->next, &req->all_io);
+
+	io->io_region.sector = DMCP_BLOCK_TO_SECTOR(block) +
+				req->info->data_start;
+	io->io_region.count = data_sectors;
+	io->io_req.mem.ptr.addr = io->comp_data;
+	io->io_req.mem.type = DM_IO_KMEM;
+	io->io_req.mem.offset = 0;
+	io->io_req.bi_op = REQ_OP_READ;
+	io->io_req.bi_op_flags = (req->bio->bi_opf & REQ_FUA);
+
+	WARN_ON((io->io_region.sector + io->io_region.count)
+		>= req->info->total_sector);
+
+	dm_io(&io->io_req, 1, &io->io_region, NULL);
+}
+
+
+/*
+ * read the data corresponding to this request.
+ * @req   : the request.
+ * @reuse : the read data may be modified. So plan accordingly.
+ */
+static void dm_icomp_handle_read_existing(struct dm_icomp_req *req, bool reuse)
+{
+	u64 block_index, first_block_index;
+	u16 logical_sectors, data_sectors;
+
+	SET_REQ_STAGE(req, STAGE_READ_EXISTING);
+
+	block_index = DMCP_SECTOR_TO_BLOCK(req->bio->bi_iter.bi_sector);
+
+	while (!!!req->result &&
+		(block_index <= DMCP_SECTOR_TO_BLOCK(
+				bio_end_sector(req->bio)-1)) &&
+		(block_index < req->info->data_blocks)) {
+
+		dm_icomp_get_extent(req->info, block_index, &first_block_index,
+			&logical_sectors, &data_sectors);
+
+		if (data_sectors)
+			dm_icomp_read_one_extent(req, first_block_index,
+				logical_sectors, data_sectors, reuse);
+
+		block_index = first_block_index +
+				DMCP_SECTOR_TO_BLOCK(logical_sectors);
+	}
+}
+
+/*
+ * read existing data
+ */
+static void dm_icomp_handle_read_read_existing(struct dm_icomp_req *req)
+{
+	dm_icomp_handle_read_existing(req, false);
+
+	if (req->result)
+		return;
+
+	/* A shortcut if all data is in already */
+	if (list_empty(&req->all_io))
+		dm_icomp_handle_read_decomp(req);
+}
+
+static void dm_icomp_handle_read_request(struct dm_icomp_req *req)
+{
+	dm_icomp_get_req(req);
+
+	if (GET_REQ_STAGE(req) == STAGE_INIT) {
+		if (!dm_icomp_lock_req_range(req)) {
+			dm_icomp_put_req(req);
+			return;
+		}
+		dm_icomp_handle_read_read_existing(req);
+	} else if (GET_REQ_STAGE(req) == STAGE_READ_EXISTING) {
+		dm_icomp_handle_read_decomp(req);
+	}
+
+	dm_icomp_put_req(req);
+}
+
+static void dm_icomp_write_meta_done(void *context, unsigned long error)
+{
+	struct dm_icomp_req *req = context;
+
+	dm_icomp_put_req(req);
+}
+
+static u64 dm_icomp_block_meta_page_index(u64 block, bool end)
+{
+	u64 bits = block * DMCP_META_BITS - !!end;
+	/*
+	 * >> 5; 32 bits per entry
+	 * << 2; each entry is 4 bytes
+	 * >> PAGE_SHIFT; PAGE_SHIFT pages
+	 */
+	return bits >> (5 - 2 + PAGE_SHIFT);
+}
+
+
+/*
+ * write compressed data to the backing storage.
+ * @io : io range
+ * @sector_start : the sector on backing storage to which the
+ *	compressed data needs to be written.
+ * @meta_start: the page index of the bits corresponding to
+ * @meta_end  : start and end blocks.
+ */
+static int dm_icomp_compress_write(struct dm_icomp_io_range *io,
+		sector_t sector_start, u64 *meta_start, u64 *meta_end)
+{
+	struct dm_icomp_req *req = io->req;
+	sector_t count = DMCP_BYTES_TO_SECTOR(io->decomp_len);
+	unsigned int comp_len, ret;
+	u64 page_index;
+
+	/* comp_data must be able to accommadate a larger compress buffer */
+	ret = dm_icomp_io_range_compress(req->info, io, &comp_len);
+	if (ret < 0) {
+		req->result = -EIO;
+		return -EIO;
+	}
+	WARN_ON(comp_len > io->comp_len);
+
+	dm_icomp_get_req(req);
+
+	io->io_req.bi_op = REQ_OP_WRITE;
+	io->io_req.bi_op_flags = (req->bio->bi_opf & REQ_FUA);
+	io->io_req.mem.ptr.addr = io->comp_data;
+	io->io_req.mem.type = DM_IO_KMEM;
+	io->io_req.mem.offset = 0;
+	io->io_region.count = DMCP_BYTES_TO_SECTOR(comp_len);
+	io->io_region.sector = sector_start + req->info->data_start;
+
+	dm_icomp_release_decomp_buffer(io);
+
+
+	WARN_ON((io->io_region.sector + io->io_region.count)
+			>= req->info->total_sector);
+
+	dm_io(&io->io_req, 1, &io->io_region, NULL);
+
+	/* update the meta data bits */
+	dm_icomp_set_extent(req, DMCP_SECTOR_TO_BLOCK(sector_start),
+		DMCP_SECTOR_TO_BLOCK(count), DMCP_BYTES_TO_SECTOR(comp_len));
+
+	page_index = dm_icomp_block_meta_page_index(
+		DMCP_SECTOR_TO_BLOCK(sector_start), false);
+	if (*meta_start > page_index)
+		*meta_start = page_index;
+
+	page_index = dm_icomp_block_meta_page_index(
+			DMCP_SECTOR_TO_BLOCK(sector_start + count), true);
+	if (*meta_end < page_index)
+		*meta_end = page_index;
+	return 0;
+}
+
+/*
+ * modify and write compressed data to the backing storage.
+ * @io : io range
+ * @meta_start: the page index of the bits corresponding to
+ * @meta_end  : start and end blocks.
+ */
+static int dm_icomp_handle_write_modify(struct dm_icomp_io_range *io,
+	u64 *meta_start, u64 *meta_end)
+{
+	struct dm_icomp_req *req = io->req;
+	sector_t bio_start, bio_end, buf_start, buf_end, overlap;
+	off_t bio_off, buf_off;
+	int ret;
+	unsigned int decomp_len;
+
+	io->io_region.sector -= req->info->data_start;
+
+	/* decompress original data */
+	if (dm_icomp_update_io_read_range(io)) {
+		req->result = -EIO;
+		return -EIO;
+	}
+
+	ret = dm_icomp_io_range_decompress(req->info, io, &decomp_len);
+	if (ret < 0) {
+		req->result = -EINVAL;
+		return -EIO;
+	}
+
+	bio_start = req->bio->bi_iter.bi_sector;
+	bio_end = bio_end_sector(req->bio) - 1;
+
+	buf_start = io->io_region.sector;
+	buf_end = buf_start + DMCP_BYTES_TO_SECTOR(decomp_len) - 1;
+
+	/* if no overlap, nothing to do. Just return */
+	if (bio_start >= buf_end || bio_end <= buf_start)
+		return 0;
+
+	bio_off = (buf_start > bio_start) ?  (buf_start - bio_start) : 0;
+	buf_off = (bio_start > buf_start) ?  (bio_start - buf_start) : 0;
+
+	/*
+	 * overlap = sizeof(block1) + sizeof(block2) - sizeof(left_side_shift) -
+	 *		sizeof(right_side_shift)  / 2  +  1
+	 */
+	overlap  =  (((bio_end - bio_start) + (buf_end - buf_start) -
+		abs(buf_end - bio_end) - abs(buf_start - bio_start)) >> 1) + 1;
+
+
+	dm_icomp_bio_copy(req->bio, DMCP_SECTOR_TO_BYTES(bio_off),
+		   io->decomp_data + DMCP_SECTOR_TO_BYTES(buf_off),
+		   DMCP_SECTOR_TO_BYTES(overlap), true);
+
+	return dm_icomp_compress_write(io, io->io_region.sector,
+			meta_start, meta_end);
+}
+
+
+/*
+ * create and write new extents. Each extent is not more than
+ * 256 sectors.
+ * @req : the request
+ * @sec_start: the start sector of the request
+ * @total  : the total sectors
+ * @list  : collect each 256 sector size io request in this list
+ * @meta_start: the page index of the bits corresponding to
+ * @meta_end  : start and end blocks.
+ *
+ */
+static void dm_icomp_handle_write_create(struct dm_icomp_req *req,
+	sector_t sec_start, sector_t total,
+	struct list_head *list, u64 *meta_start, u64 *meta_end)
+{
+	struct dm_icomp_io_range *io;
+	sector_t count, offset = 0;
+	int ret;
+
+	while (total) {
+
+		/* max i/o is 128kbytes i.e 256 sectors */
+		count = min_t(sector_t, total, 256);
+		io = dm_icomp_create_io_write_range(req, offset, count);
+		if (!io) {
+			req->result = -EIO;
+			return;
+		}
+
+		ret = dm_icomp_compress_write(io, sec_start, meta_start,
+			meta_end);
+		if (ret) {
+			dm_icomp_free_io_range(io);
+			return;
+		}
+
+
+		list_add_tail(&io->next, list);
+		total -= count;
+		sec_start += count;
+		offset += count;
+
+	}
+}
+
+/*
+ *  handle the write request.
+ */
+static void dm_icomp_handle_write_comp(struct dm_icomp_req *req)
+{
+	struct dm_icomp_io_range *io;
+	sector_t io_start, req_start, req_end;
+	u64 meta_start = -1L, meta_end = 0;
+	LIST_HEAD(newlist);
+
+	SET_REQ_STAGE(req, STAGE_WRITE_COMP);
+
+	if (req->result)
+		return;
+
+	req_start = req->bio->bi_iter.bi_sector;
+	list_for_each_entry(io, &req->all_io, next) {
+
+		io_start = io->io_region.sector - req->info->data_start;
+
+		if (req_start < io_start) {
+			/* fill the gap */
+			dm_icomp_handle_write_create(req, req_start,
+				(io_start - req_start), &newlist,
+				&meta_start, &meta_end);
+		}
+
+		dm_icomp_handle_write_modify(io, &meta_start, &meta_end);
+
+		req_start = io_start + DMCP_BYTES_TO_SECTOR(io->logical_bytes);
+	}
+
+	req_end =  bio_end_sector(req->bio);
+	if (req_start < req_end) {
+		/* fill the gap */
+		dm_icomp_handle_write_create(req, req_start,
+			 req_end-req_start, &newlist, &meta_start,
+			&meta_end);
+	}
+
+	list_splice_tail(&newlist, &req->all_io);
+
+	if (req->info->write_mode == DMCP_WRITE_THROUGH ||
+				(req->bio->bi_opf & REQ_FUA)) {
+		if (meta_start == -1)
+			return;
+		dm_icomp_get_req(req);
+		dm_icomp_write_meta(req->info, meta_start,
+			meta_end+1, req,
+			dm_icomp_write_meta_done,
+			REQ_OP_WRITE, req->bio->bi_opf);
+	}
+}
+
+/*
+ *  read the data, modify and write it back to the backing store.
+ */
+static void dm_icomp_handle_write_read_existing(struct dm_icomp_req *req)
+{
+	dm_icomp_handle_read_existing(req, true);
+	if (req->result)
+		return;
+
+	if (list_empty(&req->all_io))
+		dm_icomp_handle_write_comp(req);
+}
+
+static void dm_icomp_handle_write_request(struct dm_icomp_req *req)
+{
+	dm_icomp_get_req(req);
+
+	if (GET_REQ_STAGE(req) == STAGE_INIT) {
+		if (!dm_icomp_lock_req_range(req)) {
+			dm_icomp_put_req(req);
+			return;
+		}
+		dm_icomp_handle_write_read_existing(req);
+	} else if (GET_REQ_STAGE(req) == STAGE_READ_EXISTING) {
+		dm_icomp_handle_write_comp(req);
+	}
+
+	dm_icomp_put_req(req);
+}
+
+/* For writeback mode */
+static void dm_icomp_handle_flush_request(struct dm_icomp_req *req)
+{
+	struct writeback_flush_data wb;
+
+	atomic_set(&wb.cnt, 1);
+	init_completion(&wb.complete);
+
+	dm_icomp_flush_dirty_meta(req->info, &wb);
+
+	writeback_flush_io_done(&wb, 0);
+	wait_for_completion(&wb.complete);
+
+	req->bio->bi_error = 0;
+	bio_endio(req->bio);
+	kmem_cache_free(dm_icomp_req_cachep, req);
+}
+
+static void dm_icomp_handle_request(struct dm_icomp_req *req)
+{
+	if (req->bio->bi_opf & REQ_PREFLUSH)
+		dm_icomp_handle_flush_request(req);
+	else if (op_is_write(bio_op(req->bio)))
+		dm_icomp_handle_write_request(req);
+	else
+		dm_icomp_handle_read_request(req);
+}
+
+static void dm_icomp_do_request_work(struct work_struct *work)
+{
+	struct dm_icomp_io_worker *worker = container_of(work,
+				struct dm_icomp_io_worker, work);
+	LIST_HEAD(list);
+	struct dm_icomp_req *req;
+	struct blk_plug plug;
+	bool repeat;
+
+	blk_start_plug(&plug);
+again:
+	spin_lock_irq(&worker->lock);
+	list_splice_init(&worker->pending, &list);
+	spin_unlock_irq(&worker->lock);
+
+	repeat = !list_empty(&list);
+	while (!list_empty(&list)) {
+		req = list_first_entry(&list, struct dm_icomp_req, sibling);
+		list_del(&req->sibling);
+
+		schedule();
+		dm_icomp_handle_request(req);
+	}
+	if (repeat)
+		goto again;
+	blk_finish_plug(&plug);
+}
+
+static bool valid_request(struct bio *bio, struct dm_icomp_info *info)
+{
+	sector_t dev_end	=  info->ti->len;
+	sector_t req_end	=  bio_end_sector(bio) - 1;
+
+	return (req_end <= dev_end);
+}
+
+static int dm_icomp_map(struct dm_target *ti, struct bio *bio)
+{
+	struct dm_icomp_info *info = ti->private;
+	struct dm_icomp_req *req;
+
+	if ((bio->bi_opf & REQ_PREFLUSH) &&
+			info->write_mode == DMCP_WRITE_THROUGH) {
+		bio->bi_bdev = info->dev->bdev;
+		return DM_MAPIO_REMAPPED;
+	}
+
+
+	req = kmem_cache_alloc(dm_icomp_req_cachep, GFP_NOIO);
+	if (!req)
+		return -EIO;
+
+	req->bio = bio;
+	if (!(bio->bi_opf & REQ_PREFLUSH) && !valid_request(bio, info)) {
+		req->bio = bio;
+		req->bio->bi_error = -EINVAL;
+		bio_endio(req->bio);
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	req->info = info;
+	atomic_set(&req->io_pending, 0);
+	INIT_LIST_HEAD(&req->all_io);
+	req->result = 0;
+	SET_REQ_STAGE(req, STAGE_INIT);
+	req->locked_locks = 0;
+
+	req->cpu = raw_smp_processor_id();
+	dm_icomp_queue_req(info, req);
+
+	return DM_MAPIO_SUBMITTED;
+}
+
+static void dm_icomp_status(struct dm_target *ti, status_type_t type,
+	  unsigned int status_flags, char *result, unsigned int maxlen)
+{
+	struct dm_icomp_info *info = ti->private;
+	unsigned int sz = 0;
+
+	switch (type) {
+	case STATUSTYPE_INFO:
+		DMEMIT("%ld %ld %ld",
+			atomic64_read(&info->uncompressed_write_size),
+			atomic64_read(&info->compressed_write_size),
+			atomic64_read(&info->meta_write_size));
+		break;
+	case STATUSTYPE_TABLE:
+		if (info->write_mode == DMCP_WRITE_BACK)
+			DMEMIT("%s %s:%d %s:%s %s:%d", info->dev->name,
+				"writeback", info->writeback_delay,
+				"compressor", compressors[info->comp_alg].name,
+				"critical", info->critical);
+		else
+			DMEMIT("%s %s %s:%s %s:%d", info->dev->name,
+				"writethrough",
+				"compressor", compressors[info->comp_alg].name,
+				"critical", info->critical);
+		break;
+	}
+}
+
+static int dm_icomp_iterate_devices(struct dm_target *ti,
+				  iterate_devices_callout_fn fn, void *data)
+{
+	struct dm_icomp_info *info = ti->private;
+
+	return fn(ti, info->dev, info->data_start,
+		DMCP_BLOCK_TO_SECTOR(info->data_blocks), data);
+}
+
+static void dm_icomp_io_hints(struct dm_target *ti,
+			    struct queue_limits *limits)
+{
+	/* No blk_limits_logical_block_size */
+	limits->logical_block_size = limits->physical_block_size =
+		limits->io_min = DMCP_BLOCK_SIZE;
+	limits->max_sectors = limits->max_hw_sectors =
+		DMCP_BYTES_TO_SECTOR(DMCP_MAX_SIZE);
+}
+
+static struct target_type dm_icomp_target = {
+	.name   = "inplacecompress",
+	.version = {1, 0, 0},
+	.module = THIS_MODULE,
+	.ctr    = dm_icomp_ctr,
+	.dtr    = dm_icomp_dtr,
+	.map    = dm_icomp_map,
+	.status = dm_icomp_status,
+	.iterate_devices = dm_icomp_iterate_devices,
+	.io_hints = dm_icomp_io_hints,
+};
+
+static int __init dm_icomp_init(void)
+{
+	int r;
+
+	if (select_default_compressor())
+		return -EINVAL;
+
+	r = -ENOMEM;
+	dm_icomp_req_cachep = kmem_cache_create("dm_icomp_requests",
+		sizeof(struct dm_icomp_req), 0, 0, NULL);
+	if (!dm_icomp_req_cachep) {
+		DMWARN("Can't create request cache");
+		goto err;
+	}
+
+	dm_icomp_io_range_cachep = kmem_cache_create("dm_icomp_io_range",
+		sizeof(struct dm_icomp_io_range), 0, 0, NULL);
+	if (!dm_icomp_io_range_cachep) {
+		DMWARN("Can't create io_range cache");
+		goto err;
+	}
+
+	dm_icomp_meta_io_cachep = kmem_cache_create("dm_icomp_meta_io",
+		sizeof(struct dm_icomp_meta_io), 0, 0, NULL);
+	if (!dm_icomp_meta_io_cachep) {
+		DMWARN("Can't create meta_io cache");
+		goto err;
+	}
+
+	dm_icomp_wq = alloc_workqueue("dm_icomp_io",
+		WQ_UNBOUND|WQ_MEM_RECLAIM|WQ_CPU_INTENSIVE, 0);
+	if (!dm_icomp_wq) {
+		DMWARN("Can't create io workqueue");
+		goto err;
+	}
+
+	r = dm_register_target(&dm_icomp_target);
+	if (r < 0) {
+		DMWARN("target registration failed");
+		goto err;
+	}
+
+	for_each_possible_cpu(r) {
+		INIT_LIST_HEAD(&dm_icomp_io_workers[r].pending);
+		spin_lock_init(&dm_icomp_io_workers[r].lock);
+		INIT_WORK(&dm_icomp_io_workers[r].work,
+				dm_icomp_do_request_work);
+	}
+	return 0;
+err:
+	kmem_cache_destroy(dm_icomp_req_cachep);
+	kmem_cache_destroy(dm_icomp_io_range_cachep);
+	kmem_cache_destroy(dm_icomp_meta_io_cachep);
+	if (dm_icomp_wq)
+		destroy_workqueue(dm_icomp_wq);
+
+	return r;
+}
+
+static void __exit dm_icomp_exit(void)
+{
+	dm_unregister_target(&dm_icomp_target);
+	kmem_cache_destroy(dm_icomp_req_cachep);
+	kmem_cache_destroy(dm_icomp_io_range_cachep);
+	kmem_cache_destroy(dm_icomp_meta_io_cachep);
+	destroy_workqueue(dm_icomp_wq);
+}
+
+module_init(dm_icomp_init);
+module_exit(dm_icomp_exit);
+
+MODULE_AUTHOR("Shaohua Li <shli@xxxxxxxxxx>");
+MODULE_DESCRIPTION(DM_NAME " target with data inplace-compression");
+MODULE_LICENSE("GPL");
diff --git a/drivers/md/dm-inplace-compress.h b/drivers/md/dm-inplace-compress.h
new file mode 100644
index 0000000..757799a
--- /dev/null
+++ b/drivers/md/dm-inplace-compress.h
@@ -0,0 +1,187 @@
+#ifndef __DM_INPLACE_COMPRESS_H__
+#define __DM_INPLACE_COMPRESS_H__
+#include <linux/types.h>
+
+#define DMCP_SUPER_MAGIC 0x106526c206506c09
+#define DMCP_COMPRESS_MAGIC 0xfaceecaf
+struct dm_icomp_super_block {
+	__le64 magic;
+	__le64 meta_blocks;
+	__le64 data_blocks;
+	u8 comp_alg;
+} __packed;
+
+#define DMCP_COMP_ALG_LZO 1
+#define DMCP_COMP_ALG_842 0
+
+#ifdef __KERNEL__
+/*
+ * Minium logical size of this target is 4096 byte, which is a block.
+ * Data of a block is compressed. Compressed data is round up to 512B, which is
+ * the payload. For each block, we have 5 bits meta data. bit 0 - 3 stands
+ * payload length(0 - 8 sectors). If compressed payload length is 8 sectors, we
+ * just store uncompressed data. Actual compressed data length is stored at the
+ * last 32 bits of payload if data is compressed. In disk, payload is stored at
+ * the beginning of logical sector of the block. If IO size is bigger than one
+ * block, we store the whole data as an extent. Bit 4 stands tail for an
+ * extent. Max allowed extent size is 128k.
+ */
+#define DMCP_BLOCK_SHIFT	12
+#define DMCP_BLOCK_SIZE		(1 << DMCP_BLOCK_SHIFT)
+#define DMCP_SECTOR_SHIFT	SECTOR_SHIFT
+#define DMCP_SECTOR_SIZE	(1 << SECTOR_SHIFT)
+#define DMCP_BLOCK_SECTOR_SHIFT (DMCP_BLOCK_SHIFT - DMCP_SECTOR_SHIFT)
+#define DMCP_BLOCK_TO_SECTOR(b) ((b) << DMCP_BLOCK_SECTOR_SHIFT)
+#define DMCP_SECTOR_TO_BLOCK(s) ((s) >> DMCP_BLOCK_SECTOR_SHIFT)
+#define DMCP_SECTOR_TO_BYTES(s) ((s) << DMCP_SECTOR_SHIFT)
+#define DMCP_BYTES_TO_SECTOR(b) ((b) >> DMCP_SECTOR_SHIFT)
+#define DMCP_BYTES_TO_BLOCK(b)	((b) >> DMCP_BLOCK_SHIFT)
+
+#define DMCP_MIN_SIZE	DMCP_BLOCK_SIZE
+#define DMCP_MAX_SIZE	(128 * 2 * DMCP_SECTOR_SIZE) /* 128k */
+
+#define DMCP_BITS_PER_ENTRY	32
+#define DMCP_META_BITS		5
+#define DMCP_LENGTH_BITS	4
+#define DMCP_TAIL_MASK		(1 << DMCP_LENGTH_BITS)
+#define DMCP_LENGTH_MASK	(DMCP_TAIL_MASK - 1)
+
+#define DMCP_META_START_SECTOR (DMCP_BLOCK_SIZE >> DMCP_SECTOR_SHIFT)
+
+enum DMCP_WRITE_MODE {
+	DMCP_WRITE_BACK,
+	DMCP_WRITE_THROUGH,
+};
+
+/*
+ * a lock spans 128 blocks i.e 512kbytes.
+ * max I/O is 128K, which can at-most span two locks.
+ */
+#define BITMAP_HASH_SHIFT 7
+#define BITMAP_HASH_LEN (1<<6)
+#define BITMAP_HASH_MASK (BITMAP_HASH_LEN - 1)
+struct dm_icomp_hash_lock {
+	int io_running;
+	spinlock_t wait_lock;
+	struct list_head wait_list;
+};
+
+struct dm_icomp_info {
+	struct dm_target *ti;
+	struct dm_dev *dev;
+
+	int comp_alg;
+	bool critical;
+	struct crypto_comp *tfm[NR_CPUS];
+
+	sector_t total_sector;	/* total sectors in the backing store */
+	sector_t data_start;
+	u64 data_blocks;
+	u64 no_of_sectors;
+
+	u32 *meta_bitmap;
+	u64 meta_bitmap_bits;
+	u64 meta_bitmap_pages;
+	struct dm_icomp_hash_lock bitmap_locks[BITMAP_HASH_LEN];
+
+	enum DMCP_WRITE_MODE write_mode;
+	unsigned int writeback_delay; /* second */
+	struct task_struct *writeback_tsk;
+	struct dm_io_client *io_client;
+
+	atomic64_t compressed_write_size;
+	atomic64_t uncompressed_write_size;
+	atomic64_t meta_write_size;
+};
+
+struct dm_icomp_meta_io {
+	struct dm_io_request io_req;
+	struct dm_io_region io_region;
+	void *data;
+	void (*fn)(void *data, unsigned long error);
+};
+
+struct dm_icomp_io_range {
+	struct dm_io_request io_req;
+	struct dm_io_region io_region;
+	bool decomp_kmap;	     /* Is the decomp_data kmapped'? */
+	void *decomp_data;
+	void *decomp_real_data;      /* holds the actual start of the buffer */
+	unsigned int decomp_len;     /* actual allocated/mapped length */
+	unsigned int logical_bytes;  /* decompressed size of the extent */
+	bool comp_kmap;		     /* Is the comp_data kmapped'? */
+	void *comp_data;
+	void *comp_real_data;	     /* holds the actual start of the buffer */
+	unsigned int comp_len;	     /* actual allocated/mapped length */
+	unsigned int data_bytes;     /* compressed size of the extent */
+	struct list_head next;
+	struct dm_icomp_req *req;
+};
+
+enum DMCP_REQ_STAGE {
+	STAGE_INIT,
+	STAGE_READ_EXISTING,
+	STAGE_READ_DECOMP,
+	STAGE_WRITE_COMP,
+	STAGE_DONE,
+};
+
+struct dm_icomp_req {
+	struct bio *bio;
+	struct dm_icomp_info *info;
+	struct list_head sibling;
+	struct list_head all_io;
+	atomic_t io_pending;
+	enum DMCP_REQ_STAGE stage;
+	struct dm_icomp_hash_lock *locks[2];
+	int locked_locks;
+	int result;
+	int cpu;
+	struct work_struct work;
+};
+
+struct dm_icomp_io_worker {
+	struct list_head pending;
+	spinlock_t lock;
+	struct work_struct work;
+};
+
+struct dm_icomp_compressor_data {
+	char *name;
+	bool can_handle_overflow;
+	int (*comp_len)(int comp_len);
+	int (*max_comp_len)(int comp_len);
+};
+
+static inline int lzo_comp_len(int comp_len)
+{
+	/* lzo compression overshoots the comp buffer
+	 * if the buffer size is insufficient.
+	 * Once that bug is fixed we can return half
+	 * the length.
+	 *
+	 * return lzo1x_worst_compress(comp_len) >> 1;
+	 *
+	 * For now its the full length.
+	 */
+	return lzo1x_worst_compress(comp_len);
+}
+
+static inline int lzo_max_comp_len(int comp_len)
+{
+	return lzo1x_worst_compress(comp_len);
+}
+
+static inline int nx842_comp_len(int comp_len)
+{
+	return (comp_len >> 1);
+}
+
+static inline int nx842_max_comp_len(int comp_len)
+{
+	return comp_len;
+}
+
+#endif /* __KERNEL__ */
+
+#endif /* __DM_INPLACE_COMPRESS_H__ */
-- 
1.8.3.1