[RFC PATCH 3/3] zram: list and select compression algorithms

[Sergey Senozhatsky]

Add compressor device attr that allows to list and select
compression algorithms.

Define and make available for selection LZ4 compressor ops.

usage example:
List available compression algorithms (currently selected
one is LZO):
  cat /sys/block/zram0/compressor
  <lzo> lz4

Change compression algorithm to LZ4:
  echo lz4 > /sys/block/zram0/compressor
  cat /sys/block/zram0/compressor
  lzo <lz4>

Update documentation with "Select compression algorithm" section

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
---
 Documentation/blockdev/zram.txt | 23 ++++++++++++++++-----
 drivers/block/zram/Kconfig      |  2 ++
 drivers/block/zram/zram_drv.c   | 46 +++++++++++++++++++++++++++++++++++++----
 3 files changed, 62 insertions(+), 9 deletions(-)

diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 393541be..af90d29 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -21,7 +21,20 @@ Following shows a typical sequence of steps for using zram.
 	This creates 4 devices: /dev/zram{0,1,2,3}
 	(num_devices parameter is optional. Default: 1)
 
-2) Set Disksize
+2) Select compression algorithm
+'compressor' sysfs node allows to see available, currently used
+and change compression algorithms.
+In order to list available compression algorithms (currently selected
+one is LZO):
+	cat /sys/block/zram0/compressor
+	<lzo> lz4
+
+Change compression algorithm to LZ4:
+	echo lz4 > /sys/block/zram0/compressor
+	cat /sys/block/zram0/compressor
+	lzo <lz4>
+
+3) Set Disksize
         Set disk size by writing the value to sysfs node 'disksize'.
         The value can be either in bytes or you can use mem suffixes.
         Examples:
@@ -38,14 +51,14 @@ There is little point creating a zram of greater than twice the size of memory
 since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
 size of the disk when not in use so a huge zram is wasteful.
 
-3) Activate:
+4) Activate:
 	mkswap /dev/zram0
 	swapon /dev/zram0
 
 	mkfs.ext4 /dev/zram1
 	mount /dev/zram1 /tmp
 
-4) Stats:
+5) Stats:
 	Per-device statistics are exported as various nodes under
 	/sys/block/zram<id>/
 		disksize
@@ -59,11 +72,11 @@ size of the disk when not in use so a huge zram is wasteful.
 		compr_data_size
 		mem_used_total
 
-5) Deactivate:
+6) Deactivate:
 	swapoff /dev/zram0
 	umount /dev/zram1
 
-6) Reset:
+7) Reset:
 	Write any positive value to 'reset' sysfs node
 	echo 1 > /sys/block/zram0/reset
 	echo 1 > /sys/block/zram1/reset
diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
index 3450be8..09dacd6 100644
--- a/drivers/block/zram/Kconfig
+++ b/drivers/block/zram/Kconfig
@@ -3,6 +3,8 @@ config ZRAM
 	depends on BLOCK && SYSFS && ZSMALLOC
 	select LZO_COMPRESS
 	select LZO_DECOMPRESS
+	select LZ4_COMPRESS
+	select LZ4_DECOMPRESS
 	default n
 	help
 	  Creates virtual block devices called /dev/zramX (X = 0, 1, ...).
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 4f2c748..f1434f8 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -31,6 +31,7 @@
 #include <linux/string.h>
 #include <linux/vmalloc.h>
 #include <linux/lzo.h>
+#include <linux/lz4.h>
 
 #include "zram_drv.h"
 
@@ -47,6 +48,12 @@ static struct zram_compress_ops lzo_compressor = {
 	.decompress = lzo1x_decompress_safe,
 };
 
+static struct zram_compress_ops lz4_compressor = {
+	.workmem_sz = LZ4_MEM_COMPRESS,
+	.compress = lz4_compress,
+	.decompress = lz4_decompress_unknownoutputsize,
+};
+
 #define ZRAM_ATTR_RO(name)						\
 static ssize_t zram_attr_##name##_show(struct device *d,		\
 				struct device_attribute *attr, char *b)	\
@@ -113,6 +120,34 @@ static ssize_t mem_used_total_show(struct device *dev,
 	return sprintf(buf, "%llu\n", val);
 }
 
+static ssize_t compressor_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+	if (zram->ops == &lzo_compressor)
+		return sprintf(buf, "<lzo> lz4\n");
+	return sprintf(buf, "lzo <lz4>\n");
+}
+
+static ssize_t compressor_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+
+	down_write(&zram->init_lock);
+	if (init_done(zram)) {
+		up_write(&zram->init_lock);
+		pr_info("Cannot change compressor for initialized device\n");
+		return -EBUSY;
+	}
+	if (strncmp(buf, "lzo", 3) == 0)
+		zram->ops = &lzo_compressor;
+	else
+		zram->ops = &lz4_compressor;
+	up_write(&zram->init_lock);
+	return len;
+}
+
 /* flag operations needs meta->tb_lock */
 static int zram_test_flag(struct zram_meta *meta, u32 index,
 			enum zram_pageflags flag)
@@ -285,7 +320,7 @@ static void zram_free_page(struct zram *zram, size_t index)
 
 static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
 {
-	int ret = LZO_E_OK;
+	int ret = 0;
 	size_t clen = PAGE_SIZE;
 	unsigned char *cmem;
 	struct zram_meta *meta = zram->meta;
@@ -311,7 +346,7 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
 	read_unlock(&meta->tb_lock);
 
 	/* Should NEVER happen. Return bio error if it does. */
-	if (unlikely(ret != LZO_E_OK)) {
+	if (unlikely(ret)) {
 		pr_err("Decompression failed! err=%d, page=%u\n", ret, index);
 		atomic64_inc(&zram->stats.failed_reads);
 		return ret;
@@ -354,7 +389,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 
 	ret = zram_decompress_page(zram, uncmem, index);
 	/* Should NEVER happen. Return bio error if it does. */
-	if (unlikely(ret != LZO_E_OK))
+	if (unlikely(ret))
 		goto out_cleanup;
 
 	if (is_partial_io(bvec))
@@ -433,7 +468,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 		uncmem = NULL;
 	}
 
-	if (unlikely(ret != LZO_E_OK)) {
+	if (unlikely(ret)) {
 		pr_err("Compression failed! err=%d\n", ret);
 		goto out;
 	}
@@ -705,6 +740,8 @@ static DEVICE_ATTR(initstate, S_IRUGO, initstate_show, NULL);
 static DEVICE_ATTR(reset, S_IWUSR, NULL, reset_store);
 static DEVICE_ATTR(orig_data_size, S_IRUGO, orig_data_size_show, NULL);
 static DEVICE_ATTR(mem_used_total, S_IRUGO, mem_used_total_show, NULL);
+static DEVICE_ATTR(compressor, S_IRUGO | S_IWUSR,
+		compressor_show, compressor_store);
 
 ZRAM_ATTR_RO(num_reads);
 ZRAM_ATTR_RO(num_writes);
@@ -719,6 +756,7 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_disksize.attr,
 	&dev_attr_initstate.attr,
 	&dev_attr_reset.attr,
+	&dev_attr_compressor.attr,
 	&dev_attr_num_reads.attr,
 	&dev_attr_num_writes.attr,
 	&dev_attr_failed_reads.attr,
-- 
1.8.5.3.493.gb139ac2

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