[PATCH v4 1/4] zram: Fix deadlock bug in partial write

[PATCH v4 1/4] zram: Fix deadlock bug in partial write

[Minchan Kim]

Now zram allocates new page with GFP_KERNEL in zram I/O path
if IO is partial. Unfortunately, It may cuase deadlock with
reclaim path so this patch solves the problem.

Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
---

We could use GFP_IO instead of GFP_ATOMIC in zram_bvec_read with
some modification related to buffer allocation in case of partial IO.
But it needs more churn and prevent merge this patch into stable
if we should send this to stable so I'd like to keep it as simple
as possbile. GFP_IO usage could be separate patch after we merge it.
Thanks.

 drivers/staging/zram/zram_drv.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 61fb8f1..b285b3a 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -220,7 +220,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 	user_mem = kmap_atomic(page);
 	if (is_partial_io(bvec))
 		/* Use  a temporary buffer to decompress the page */
-		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
+		uncmem = kmalloc(PAGE_SIZE, GFP_ATOMIC);
 	else
 		uncmem = user_mem;
 
@@ -268,7 +268,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 		 * This is a partial IO. We need to read the full page
 		 * before to write the changes.
 		 */
-		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
+		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
 		if (!uncmem) {
 			pr_info("Error allocating temp memory!\n");
 			ret = -ENOMEM;
-- 
1.7.9.5

[PATCH v4 1/4] zram: Fix deadlock bug in partial write

[Minchan Kim]

Now zram allocates new page with GFP_KERNEL in zram I/O path
if IO is partial. Unfortunately, It may cuase deadlock with
reclaim path so this patch solves the problem.

Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
---

We could use GFP_IO instead of GFP_ATOMIC in zram_bvec_read with
some modification related to buffer allocation in case of partial IO.
But it needs more churn and prevent merge this patch into stable
if we should send this to stable so I'd like to keep it as simple
as possbile. GFP_IO usage could be separate patch after we merge it.
Thanks.

 drivers/staging/zram/zram_drv.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 61fb8f1..b285b3a 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -220,7 +220,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 	user_mem = kmap_atomic(page);
 	if (is_partial_io(bvec))
 		/* Use  a temporary buffer to decompress the page */
-		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
+		uncmem = kmalloc(PAGE_SIZE, GFP_ATOMIC);
 	else
 		uncmem = user_mem;
 
@@ -268,7 +268,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 		 * This is a partial IO. We need to read the full page
 		 * before to write the changes.
 		 */
-		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
+		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
 		if (!uncmem) {
 			pr_info("Error allocating temp memory!\n");
 			ret = -ENOMEM;
-- 
1.7.9.5

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[PATCH v4 2/4] zram: force disksize setting before using zram

[Minchan Kim]

Now zram document syas "set disksize is optional"
but partly it's wrong. When you try to use zram firstly after
booting, you must set disksize, otherwise zram can't work because
zram gendisk's size is 0. But once you do it, you can use zram freely
after reset because reset doesn't reset to zero paradoxically.
So in this time, disksize setting is optional.:(
It's inconsitent for user behavior and not straightforward.

This patch forces always setting disksize firstly before using zram.
Yes. It changes current behavior so someone could complain when
he upgrades zram. Apparently it could be a problem if zram is mainline
but it still lives in staging so behavior could be changed for right
way to go. Let them excuse.

Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 drivers/staging/zram/zram.txt     |   27 ++++++++++----------
 drivers/staging/zram/zram_drv.c   |   51 +++++++++++++------------------------
 drivers/staging/zram/zram_drv.h   |    5 +---
 drivers/staging/zram/zram_sysfs.c |    6 +----
 4 files changed, 34 insertions(+), 55 deletions(-)

diff --git a/drivers/staging/zram/zram.txt b/drivers/staging/zram/zram.txt
index 5f75d29..765d790 100644
--- a/drivers/staging/zram/zram.txt
+++ b/drivers/staging/zram/zram.txt
@@ -23,17 +23,17 @@ 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 (Optional):
-	Set disk size by writing the value to sysfs node 'disksize'
-	(in bytes). If disksize is not given, default value of 25%
-	of RAM is used.
-
-	# Initialize /dev/zram0 with 50MB disksize
-	echo $((50*1024*1024)) > /sys/block/zram0/disksize
-
-	NOTE: disksize cannot be changed if the disk contains any
-	data. So, for such a disk, you need to issue 'reset' (see below)
-	before you can change its disksize.
+2) 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:
+            # Initialize /dev/zram0 with 50MB disksize
+            echo $((50*1024*1024)) > /sys/block/zram0/disksize
+
+            # Using mem suffixes
+            echo 256K > /sys/block/zram0/disksize
+            echo 512M > /sys/block/zram0/disksize
+            echo 1G > /sys/block/zram0/disksize
 
 3) Activate:
 	mkswap /dev/zram0
@@ -65,8 +65,9 @@ Following shows a typical sequence of steps for using zram.
 	echo 1 > /sys/block/zram0/reset
 	echo 1 > /sys/block/zram1/reset
 
-	(This frees all the memory allocated for the given device).
-
+	This frees all the memory allocated for the given device and
+	resets the disksize to zero. You must set the disksize again
+	before reusing the device.
 
 Please report any problems at:
  - Mailing list: linux-mm-cc at laptop dot org
diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index b285b3a..f8ae1bf 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -94,34 +94,6 @@ static int page_zero_filled(void *ptr)
 	return 1;
 }
 
-static void zram_set_disksize(struct zram *zram, size_t totalram_bytes)
-{
-	if (!zram->disksize) {
-		pr_info(
-		"disk size not provided. You can use disksize_kb module "
-		"param to specify size.\nUsing default: (%u%% of RAM).\n",
-		default_disksize_perc_ram
-		);
-		zram->disksize = default_disksize_perc_ram *
-					(totalram_bytes / 100);
-	}
-
-	if (zram->disksize > 2 * (totalram_bytes)) {
-		pr_info(
-		"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.\n"
-		"\tMemory Size: %zu kB\n"
-		"\tSize you selected: %llu kB\n"
-		"Continuing anyway ...\n",
-		totalram_bytes >> 10, zram->disksize >> 10);
-	}
-
-	zram->disksize &= PAGE_MASK;
-}
-
 static void zram_free_page(struct zram *zram, size_t index)
 {
 	unsigned long handle = zram->table[index].handle;
@@ -495,6 +467,9 @@ void __zram_reset_device(struct zram *zram)
 {
 	size_t index;
 
+	if (!zram->init_done)
+		return;
+
 	zram->init_done = 0;
 
 	/* Free various per-device buffers */
@@ -523,6 +498,7 @@ void __zram_reset_device(struct zram *zram)
 	memset(&zram->stats, 0, sizeof(zram->stats));
 
 	zram->disksize = 0;
+	set_capacity(zram->disk, 0);
 }
 
 void zram_reset_device(struct zram *zram)
@@ -544,7 +520,19 @@ int zram_init_device(struct zram *zram)
 		return 0;
 	}
 
-	zram_set_disksize(zram, totalram_pages << PAGE_SHIFT);
+	if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
+		pr_info(
+		"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.\n"
+		"\tMemory Size: %zu kB\n"
+		"\tSize you selected: %llu kB\n"
+		"Continuing anyway ...\n",
+		(totalram_pages << PAGE_SHIFT) >> 10, zram->disksize >> 10
+		);
+	}
 
 	zram->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
 	if (!zram->compress_workmem) {
@@ -569,8 +557,6 @@ int zram_init_device(struct zram *zram)
 		goto fail_no_table;
 	}
 
-	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
-
 	/* zram devices sort of resembles non-rotational disks */
 	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
 
@@ -749,8 +735,7 @@ static void __exit zram_exit(void)
 		zram = &zram_devices[i];
 
 		destroy_device(zram);
-		if (zram->init_done)
-			zram_reset_device(zram);
+		zram_reset_device(zram);
 	}
 
 	unregister_blkdev(zram_major, "zram");
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index df2eec4..5b671d1 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -28,9 +28,6 @@ static const unsigned max_num_devices = 32;
 
 /*-- Configurable parameters */
 
-/* Default zram disk size: 25% of total RAM */
-static const unsigned default_disksize_perc_ram = 25;
-
 /*
  * Pages that compress to size greater than this are stored
  * uncompressed in memory.
@@ -115,6 +112,6 @@ extern struct attribute_group zram_disk_attr_group;
 #endif
 
 extern int zram_init_device(struct zram *zram);
-extern void __zram_reset_device(struct zram *zram);
+extern void zram_reset_device(struct zram *zram);
 
 #endif
diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index de1eacf..4143af9 100644
--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -110,11 +110,7 @@ static ssize_t reset_store(struct device *dev,
 	if (bdev)
 		fsync_bdev(bdev);
 
-	down_write(&zram->init_lock);
-	if (zram->init_done)
-		__zram_reset_device(zram);
-	up_write(&zram->init_lock);
-
+	zram_reset_device(zram);
 	return len;
 }
 
-- 
1.7.9.5

[PATCH v4 2/4] zram: force disksize setting before using zram

[Minchan Kim]

Now zram document syas "set disksize is optional"
but partly it's wrong. When you try to use zram firstly after
booting, you must set disksize, otherwise zram can't work because
zram gendisk's size is 0. But once you do it, you can use zram freely
after reset because reset doesn't reset to zero paradoxically.
So in this time, disksize setting is optional.:(
It's inconsitent for user behavior and not straightforward.

This patch forces always setting disksize firstly before using zram.
Yes. It changes current behavior so someone could complain when
he upgrades zram. Apparently it could be a problem if zram is mainline
but it still lives in staging so behavior could be changed for right
way to go. Let them excuse.

Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 drivers/staging/zram/zram.txt     |   27 ++++++++++----------
 drivers/staging/zram/zram_drv.c   |   51 +++++++++++++------------------------
 drivers/staging/zram/zram_drv.h   |    5 +---
 drivers/staging/zram/zram_sysfs.c |    6 +----
 4 files changed, 34 insertions(+), 55 deletions(-)

diff --git a/drivers/staging/zram/zram.txt b/drivers/staging/zram/zram.txt
index 5f75d29..765d790 100644
--- a/drivers/staging/zram/zram.txt
+++ b/drivers/staging/zram/zram.txt
@@ -23,17 +23,17 @@ 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 (Optional):
-	Set disk size by writing the value to sysfs node 'disksize'
-	(in bytes). If disksize is not given, default value of 25%
-	of RAM is used.
-
-	# Initialize /dev/zram0 with 50MB disksize
-	echo $((50*1024*1024)) > /sys/block/zram0/disksize
-
-	NOTE: disksize cannot be changed if the disk contains any
-	data. So, for such a disk, you need to issue 'reset' (see below)
-	before you can change its disksize.
+2) 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:
+            # Initialize /dev/zram0 with 50MB disksize
+            echo $((50*1024*1024)) > /sys/block/zram0/disksize
+
+            # Using mem suffixes
+            echo 256K > /sys/block/zram0/disksize
+            echo 512M > /sys/block/zram0/disksize
+            echo 1G > /sys/block/zram0/disksize
 
 3) Activate:
 	mkswap /dev/zram0
@@ -65,8 +65,9 @@ Following shows a typical sequence of steps for using zram.
 	echo 1 > /sys/block/zram0/reset
 	echo 1 > /sys/block/zram1/reset
 
-	(This frees all the memory allocated for the given device).
-
+	This frees all the memory allocated for the given device and
+	resets the disksize to zero. You must set the disksize again
+	before reusing the device.
 
 Please report any problems at:
  - Mailing list: linux-mm-cc at laptop dot org
diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index b285b3a..f8ae1bf 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -94,34 +94,6 @@ static int page_zero_filled(void *ptr)
 	return 1;
 }
 
-static void zram_set_disksize(struct zram *zram, size_t totalram_bytes)
-{
-	if (!zram->disksize) {
-		pr_info(
-		"disk size not provided. You can use disksize_kb module "
-		"param to specify size.\nUsing default: (%u%% of RAM).\n",
-		default_disksize_perc_ram
-		);
-		zram->disksize = default_disksize_perc_ram *
-					(totalram_bytes / 100);
-	}
-
-	if (zram->disksize > 2 * (totalram_bytes)) {
-		pr_info(
-		"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.\n"
-		"\tMemory Size: %zu kB\n"
-		"\tSize you selected: %llu kB\n"
-		"Continuing anyway ...\n",
-		totalram_bytes >> 10, zram->disksize >> 10);
-	}
-
-	zram->disksize &= PAGE_MASK;
-}
-
 static void zram_free_page(struct zram *zram, size_t index)
 {
 	unsigned long handle = zram->table[index].handle;
@@ -495,6 +467,9 @@ void __zram_reset_device(struct zram *zram)
 {
 	size_t index;
 
+	if (!zram->init_done)
+		return;
+
 	zram->init_done = 0;
 
 	/* Free various per-device buffers */
@@ -523,6 +498,7 @@ void __zram_reset_device(struct zram *zram)
 	memset(&zram->stats, 0, sizeof(zram->stats));
 
 	zram->disksize = 0;
+	set_capacity(zram->disk, 0);
 }
 
 void zram_reset_device(struct zram *zram)
@@ -544,7 +520,19 @@ int zram_init_device(struct zram *zram)
 		return 0;
 	}
 
-	zram_set_disksize(zram, totalram_pages << PAGE_SHIFT);
+	if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
+		pr_info(
+		"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.\n"
+		"\tMemory Size: %zu kB\n"
+		"\tSize you selected: %llu kB\n"
+		"Continuing anyway ...\n",
+		(totalram_pages << PAGE_SHIFT) >> 10, zram->disksize >> 10
+		);
+	}
 
 	zram->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
 	if (!zram->compress_workmem) {
@@ -569,8 +557,6 @@ int zram_init_device(struct zram *zram)
 		goto fail_no_table;
 	}
 
-	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
-
 	/* zram devices sort of resembles non-rotational disks */
 	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
 
@@ -749,8 +735,7 @@ static void __exit zram_exit(void)
 		zram = &zram_devices[i];
 
 		destroy_device(zram);
-		if (zram->init_done)
-			zram_reset_device(zram);
+		zram_reset_device(zram);
 	}
 
 	unregister_blkdev(zram_major, "zram");
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index df2eec4..5b671d1 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -28,9 +28,6 @@ static const unsigned max_num_devices = 32;
 
 /*-- Configurable parameters */
 
-/* Default zram disk size: 25% of total RAM */
-static const unsigned default_disksize_perc_ram = 25;
-
 /*
  * Pages that compress to size greater than this are stored
  * uncompressed in memory.
@@ -115,6 +112,6 @@ extern struct attribute_group zram_disk_attr_group;
 #endif
 
 extern int zram_init_device(struct zram *zram);
-extern void __zram_reset_device(struct zram *zram);
+extern void zram_reset_device(struct zram *zram);
 
 #endif
diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index de1eacf..4143af9 100644
--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -110,11 +110,7 @@ static ssize_t reset_store(struct device *dev,
 	if (bdev)
 		fsync_bdev(bdev);
 
-	down_write(&zram->init_lock);
-	if (zram->init_done)
-		__zram_reset_device(zram);
-	up_write(&zram->init_lock);
-
+	zram_reset_device(zram);
 	return len;
 }
 
-- 
1.7.9.5

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[PATCH v4 3/4] zram: give up lazy initialization of zram metadata

[Minchan Kim]

1) User of zram normally do mkfs.xxx or mkswap before using
   the zram block device(ex, normally, do it at booting time)
   It ends up allocating such metadata of zram before real usage so
   benefit of lazy initialzation would be mitigated.

2) Some user want to use zram when memory pressure is high.(ie, load zram
   dynamically, NOT booting time). It does make sense because people don't
   want to waste memory until memory pressure is high(ie, where zram is really
   helpful time). In this case, lazy initialzation could be failed easily
   because we will use GFP_NOIO instead of GFP_KERNEL for avoiding deadlock.
   So the benefit of lazy initialzation would be mitigated, too.

3) Metadata overhead is not critical and Nitin has a plan to diet it.
   4K : 12 byte(64bit machine) -> 64G : 192M so 0.3% isn't big overhead
   If insane user use such big zram device up to 20, it could consume 6% of ram
   but efficieny of zram will cover the waste.

So this patch gives up lazy initialization and instead we initialize metadata
at disksize setting time.

Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 drivers/staging/zram/zram_drv.c   |   20 ++++----------------
 drivers/staging/zram/zram_sysfs.c |    1 +
 2 files changed, 5 insertions(+), 16 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index f8ae1bf..4264121 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -440,16 +440,13 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
 {
 	struct zram *zram = queue->queuedata;
 
-	if (unlikely(!zram->init_done) && zram_init_device(zram))
-		goto error;
-
 	down_read(&zram->init_lock);
 	if (unlikely(!zram->init_done))
-		goto error_unlock;
+		goto error;
 
 	if (!valid_io_request(zram, bio)) {
 		zram_stat64_inc(zram, &zram->stats.invalid_io);
-		goto error_unlock;
+		goto error;
 	}
 
 	__zram_make_request(zram, bio, bio_data_dir(bio));
@@ -457,9 +454,8 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
 
 	return;
 
-error_unlock:
-	up_read(&zram->init_lock);
 error:
+	up_read(&zram->init_lock);
 	bio_io_error(bio);
 }
 
@@ -508,18 +504,12 @@ void zram_reset_device(struct zram *zram)
 	up_write(&zram->init_lock);
 }
 
+/* zram->init_lock should be held */
 int zram_init_device(struct zram *zram)
 {
 	int ret;
 	size_t num_pages;
 
-	down_write(&zram->init_lock);
-
-	if (zram->init_done) {
-		up_write(&zram->init_lock);
-		return 0;
-	}
-
 	if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
 		pr_info(
 		"There is little point creating a zram of greater than "
@@ -568,7 +558,6 @@ int zram_init_device(struct zram *zram)
 	}
 
 	zram->init_done = 1;
-	up_write(&zram->init_lock);
 
 	pr_debug("Initialization done!\n");
 	return 0;
@@ -578,7 +567,6 @@ fail_no_table:
 	zram->disksize = 0;
 fail:
 	__zram_reset_device(zram);
-	up_write(&zram->init_lock);
 	pr_err("Initialization failed: err=%d\n", ret);
 	return ret;
 }
diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index 4143af9..369db12 100644
--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -71,6 +71,7 @@ static ssize_t disksize_store(struct device *dev,
 
 	zram->disksize = PAGE_ALIGN(disksize);
 	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
+	zram_init_device(zram);
 	up_write(&zram->init_lock);
 
 	return len;
-- 
1.7.9.5

[PATCH v4 3/4] zram: give up lazy initialization of zram metadata

[Minchan Kim]

1) User of zram normally do mkfs.xxx or mkswap before using
   the zram block device(ex, normally, do it at booting time)
   It ends up allocating such metadata of zram before real usage so
   benefit of lazy initialzation would be mitigated.

2) Some user want to use zram when memory pressure is high.(ie, load zram
   dynamically, NOT booting time). It does make sense because people don't
   want to waste memory until memory pressure is high(ie, where zram is really
   helpful time). In this case, lazy initialzation could be failed easily
   because we will use GFP_NOIO instead of GFP_KERNEL for avoiding deadlock.
   So the benefit of lazy initialzation would be mitigated, too.

3) Metadata overhead is not critical and Nitin has a plan to diet it.
   4K : 12 byte(64bit machine) -> 64G : 192M so 0.3% isn't big overhead
   If insane user use such big zram device up to 20, it could consume 6% of ram
   but efficieny of zram will cover the waste.

So this patch gives up lazy initialization and instead we initialize metadata
at disksize setting time.

Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 drivers/staging/zram/zram_drv.c   |   20 ++++----------------
 drivers/staging/zram/zram_sysfs.c |    1 +
 2 files changed, 5 insertions(+), 16 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index f8ae1bf..4264121 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -440,16 +440,13 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
 {
 	struct zram *zram = queue->queuedata;
 
-	if (unlikely(!zram->init_done) && zram_init_device(zram))
-		goto error;
-
 	down_read(&zram->init_lock);
 	if (unlikely(!zram->init_done))
-		goto error_unlock;
+		goto error;
 
 	if (!valid_io_request(zram, bio)) {
 		zram_stat64_inc(zram, &zram->stats.invalid_io);
-		goto error_unlock;
+		goto error;
 	}
 
 	__zram_make_request(zram, bio, bio_data_dir(bio));
@@ -457,9 +454,8 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
 
 	return;
 
-error_unlock:
-	up_read(&zram->init_lock);
 error:
+	up_read(&zram->init_lock);
 	bio_io_error(bio);
 }
 
@@ -508,18 +504,12 @@ void zram_reset_device(struct zram *zram)
 	up_write(&zram->init_lock);
 }
 
+/* zram->init_lock should be held */
 int zram_init_device(struct zram *zram)
 {
 	int ret;
 	size_t num_pages;
 
-	down_write(&zram->init_lock);
-
-	if (zram->init_done) {
-		up_write(&zram->init_lock);
-		return 0;
-	}
-
 	if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
 		pr_info(
 		"There is little point creating a zram of greater than "
@@ -568,7 +558,6 @@ int zram_init_device(struct zram *zram)
 	}
 
 	zram->init_done = 1;
-	up_write(&zram->init_lock);
 
 	pr_debug("Initialization done!\n");
 	return 0;
@@ -578,7 +567,6 @@ fail_no_table:
 	zram->disksize = 0;
 fail:
 	__zram_reset_device(zram);
-	up_write(&zram->init_lock);
 	pr_err("Initialization failed: err=%d\n", ret);
 	return ret;
 }
diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index 4143af9..369db12 100644
--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -71,6 +71,7 @@ static ssize_t disksize_store(struct device *dev,
 
 	zram->disksize = PAGE_ALIGN(disksize);
 	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
+	zram_init_device(zram);
 	up_write(&zram->init_lock);
 
 	return len;
-- 
1.7.9.5

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[PATCH v4 4/4] zram: get rid of lockdep warning

[Minchan Kim]

Lockdep complains about recursive deadlock of zram->init_lock.
[1] in this thread made it false positive because we can't request IO to zram
before setting disksize. Anyway, we should shut lockdep up to
avoid many reporting from user.

[1] zram: force disksize setting before using zram

Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 drivers/staging/zram/zram_drv.c   |  189 +++++++++++++++++++------------------
 drivers/staging/zram/zram_drv.h   |   12 ++-
 drivers/staging/zram/zram_sysfs.c |   11 ++-
 3 files changed, 116 insertions(+), 96 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 4264121..0a7fc8d 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -61,22 +61,22 @@ static void zram_stat64_inc(struct zram *zram, u64 *v)
 	zram_stat64_add(zram, v, 1);
 }
 
-static int zram_test_flag(struct zram *zram, u32 index,
+static int zram_test_flag(struct zram_meta *meta, u32 index,
 			enum zram_pageflags flag)
 {
-	return zram->table[index].flags & BIT(flag);
+	return meta->table[index].flags & BIT(flag);
 }
 
-static void zram_set_flag(struct zram *zram, u32 index,
+static void zram_set_flag(struct zram_meta *meta, u32 index,
 			enum zram_pageflags flag)
 {
-	zram->table[index].flags |= BIT(flag);
+	meta->table[index].flags |= BIT(flag);
 }
 
-static void zram_clear_flag(struct zram *zram, u32 index,
+static void zram_clear_flag(struct zram_meta *meta, u32 index,
 			enum zram_pageflags flag)
 {
-	zram->table[index].flags &= ~BIT(flag);
+	meta->table[index].flags &= ~BIT(flag);
 }
 
 static int page_zero_filled(void *ptr)
@@ -96,16 +96,17 @@ static int page_zero_filled(void *ptr)
 
 static void zram_free_page(struct zram *zram, size_t index)
 {
-	unsigned long handle = zram->table[index].handle;
-	u16 size = zram->table[index].size;
+	struct zram_meta *meta = zram->meta;
+	unsigned long handle = meta->table[index].handle;
+	u16 size = meta->table[index].size;
 
 	if (unlikely(!handle)) {
 		/*
 		 * No memory is allocated for zero filled pages.
 		 * Simply clear zero page flag.
 		 */
-		if (zram_test_flag(zram, index, ZRAM_ZERO)) {
-			zram_clear_flag(zram, index, ZRAM_ZERO);
+		if (zram_test_flag(meta, index, ZRAM_ZERO)) {
+			zram_clear_flag(meta, index, ZRAM_ZERO);
 			zram->stats.pages_zero--;
 		}
 		return;
@@ -114,17 +115,17 @@ static void zram_free_page(struct zram *zram, size_t index)
 	if (unlikely(size > max_zpage_size))
 		zram->stats.bad_compress--;
 
-	zs_free(zram->mem_pool, handle);
+	zs_free(meta->mem_pool, handle);
 
 	if (size <= PAGE_SIZE / 2)
 		zram->stats.good_compress--;
 
 	zram_stat64_sub(zram, &zram->stats.compr_size,
-			zram->table[index].size);
+			meta->table[index].size);
 	zram->stats.pages_stored--;
 
-	zram->table[index].handle = 0;
-	zram->table[index].size = 0;
+	meta->table[index].handle = 0;
+	meta->table[index].size = 0;
 }
 
 static void handle_zero_page(struct bio_vec *bvec)
@@ -149,20 +150,21 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
 	int ret = LZO_E_OK;
 	size_t clen = PAGE_SIZE;
 	unsigned char *cmem;
-	unsigned long handle = zram->table[index].handle;
+	struct zram_meta *meta = zram->meta;
+	unsigned long handle = meta->table[index].handle;
 
-	if (!handle || zram_test_flag(zram, index, ZRAM_ZERO)) {
+	if (!handle || zram_test_flag(meta, index, ZRAM_ZERO)) {
 		memset(mem, 0, PAGE_SIZE);
 		return 0;
 	}
 
-	cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
-	if (zram->table[index].size == PAGE_SIZE)
+	cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_RO);
+	if (meta->table[index].size == PAGE_SIZE)
 		memcpy(mem, cmem, PAGE_SIZE);
 	else
-		ret = lzo1x_decompress_safe(cmem, zram->table[index].size,
+		ret = lzo1x_decompress_safe(cmem, meta->table[index].size,
 						mem, &clen);
-	zs_unmap_object(zram->mem_pool, handle);
+	zs_unmap_object(meta->mem_pool, handle);
 
 	/* Should NEVER happen. Return bio error if it does. */
 	if (unlikely(ret != LZO_E_OK)) {
@@ -180,11 +182,11 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 	int ret;
 	struct page *page;
 	unsigned char *user_mem, *uncmem = NULL;
-
+	struct zram_meta *meta = zram->meta;
 	page = bvec->bv_page;
 
-	if (unlikely(!zram->table[index].handle) ||
-			zram_test_flag(zram, index, ZRAM_ZERO)) {
+	if (unlikely(!meta->table[index].handle) ||
+			zram_test_flag(meta, index, ZRAM_ZERO)) {
 		handle_zero_page(bvec);
 		return 0;
 	}
@@ -231,9 +233,10 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	unsigned long handle;
 	struct page *page;
 	unsigned char *user_mem, *cmem, *src, *uncmem = NULL;
+	struct zram_meta *meta = zram->meta;
 
 	page = bvec->bv_page;
-	src = zram->compress_buffer;
+	src = meta->compress_buffer;
 
 	if (is_partial_io(bvec)) {
 		/*
@@ -255,8 +258,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	 * System overwrites unused sectors. Free memory associated
 	 * with this sector now.
 	 */
-	if (zram->table[index].handle ||
-	    zram_test_flag(zram, index, ZRAM_ZERO))
+	if (meta->table[index].handle ||
+	    zram_test_flag(meta, index, ZRAM_ZERO))
 		zram_free_page(zram, index);
 
 	user_mem = kmap_atomic(page);
@@ -274,13 +277,13 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 		if (!is_partial_io(bvec))
 			kunmap_atomic(user_mem);
 		zram->stats.pages_zero++;
-		zram_set_flag(zram, index, ZRAM_ZERO);
+		zram_set_flag(meta, index, ZRAM_ZERO);
 		ret = 0;
 		goto out;
 	}
 
 	ret = lzo1x_1_compress(uncmem, PAGE_SIZE, src, &clen,
-			       zram->compress_workmem);
+			       meta->compress_workmem);
 
 	if (!is_partial_io(bvec)) {
 		kunmap_atomic(user_mem);
@@ -301,14 +304,14 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 			src = uncmem;
 	}
 
-	handle = zs_malloc(zram->mem_pool, clen);
+	handle = zs_malloc(meta->mem_pool, clen);
 	if (!handle) {
 		pr_info("Error allocating memory for compressed "
 			"page: %u, size=%zu\n", index, clen);
 		ret = -ENOMEM;
 		goto out;
 	}
-	cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
+	cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_WO);
 
 	if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
 		src = kmap_atomic(page);
@@ -316,10 +319,10 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
 		kunmap_atomic(src);
 
-	zs_unmap_object(zram->mem_pool, handle);
+	zs_unmap_object(meta->mem_pool, handle);
 
-	zram->table[index].handle = handle;
-	zram->table[index].size = clen;
+	meta->table[index].handle = handle;
+	meta->table[index].size = clen;
 
 	/* Update stats */
 	zram_stat64_add(zram, &zram->stats.compr_size, clen);
@@ -462,34 +465,25 @@ error:
 void __zram_reset_device(struct zram *zram)
 {
 	size_t index;
+	struct zram_meta *meta;
 
 	if (!zram->init_done)
 		return;
 
+	meta = zram->meta;
 	zram->init_done = 0;
 
-	/* Free various per-device buffers */
-	kfree(zram->compress_workmem);
-	free_pages((unsigned long)zram->compress_buffer, 1);
-
-	zram->compress_workmem = NULL;
-	zram->compress_buffer = NULL;
-
 	/* Free all pages that are still in this zram device */
 	for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
-		unsigned long handle = zram->table[index].handle;
+		unsigned long handle = meta->table[index].handle;
 		if (!handle)
 			continue;
 
-		zs_free(zram->mem_pool, handle);
+		zs_free(meta->mem_pool, handle);
 	}
 
-	vfree(zram->table);
-	zram->table = NULL;
-
-	zs_destroy_pool(zram->mem_pool);
-	zram->mem_pool = NULL;
-
+	zram_meta_free(zram->meta);
+	zram->meta = NULL;
 	/* Reset stats */
 	memset(&zram->stats, 0, sizeof(zram->stats));
 
@@ -504,12 +498,65 @@ void zram_reset_device(struct zram *zram)
 	up_write(&zram->init_lock);
 }
 
-/* zram->init_lock should be held */
-int zram_init_device(struct zram *zram)
+void zram_meta_free(struct zram_meta *meta)
+{
+	zs_destroy_pool(meta->mem_pool);
+	kfree(meta->compress_workmem);
+	free_pages((unsigned long)meta->compress_buffer, 1);
+	vfree(meta->table);
+	kfree(meta);
+}
+
+struct zram_meta *zram_meta_alloc(u64 disksize)
 {
-	int ret;
 	size_t num_pages;
+	struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
+	if (!meta)
+		goto out;
+
+	meta->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
+	if (!meta->compress_workmem) {
+		pr_err("Error allocating compressor working memory!\n");
+		goto free_meta;
+	}
+
+	meta->compress_buffer =
+		(void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
+	if (!meta->compress_buffer) {
+		pr_err("Error allocating compressor buffer space\n");
+		goto free_workmem;
+	}
+
+	num_pages = disksize >> PAGE_SHIFT;
+	meta->table = vzalloc(num_pages * sizeof(*meta->table));
+	if (!meta->table) {
+		pr_err("Error allocating zram address table\n");
+		goto free_buffer;
+	}
+
+	meta->mem_pool = zs_create_pool("zram", GFP_NOIO | __GFP_HIGHMEM);
+	if (!meta->mem_pool) {
+		pr_err("Error creating memory pool\n");
+		goto free_table;
+	}
+
+	return meta;
+
+free_table:
+	vfree(meta->table);
+free_buffer:
+	free_pages((unsigned long)meta->compress_buffer, 1);
+free_workmem:
+	kfree(meta->compress_workmem);
+free_meta:
+	kfree(meta);
+	meta = NULL;
+out:
+	return meta;
+}
 
+void zram_init_device(struct zram *zram, struct zram_meta *meta)
+{
 	if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
 		pr_info(
 		"There is little point creating a zram of greater than "
@@ -524,51 +571,13 @@ int zram_init_device(struct zram *zram)
 		);
 	}
 
-	zram->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
-	if (!zram->compress_workmem) {
-		pr_err("Error allocating compressor working memory!\n");
-		ret = -ENOMEM;
-		goto fail_no_table;
-	}
-
-	zram->compress_buffer =
-		(void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
-	if (!zram->compress_buffer) {
-		pr_err("Error allocating compressor buffer space\n");
-		ret = -ENOMEM;
-		goto fail_no_table;
-	}
-
-	num_pages = zram->disksize >> PAGE_SHIFT;
-	zram->table = vzalloc(num_pages * sizeof(*zram->table));
-	if (!zram->table) {
-		pr_err("Error allocating zram address table\n");
-		ret = -ENOMEM;
-		goto fail_no_table;
-	}
-
 	/* zram devices sort of resembles non-rotational disks */
 	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
 
-	zram->mem_pool = zs_create_pool("zram", GFP_NOIO | __GFP_HIGHMEM);
-	if (!zram->mem_pool) {
-		pr_err("Error creating memory pool\n");
-		ret = -ENOMEM;
-		goto fail;
-	}
-
+	zram->meta = meta;
 	zram->init_done = 1;
 
 	pr_debug("Initialization done!\n");
-	return 0;
-
-fail_no_table:
-	/* To prevent accessing table entries during cleanup */
-	zram->disksize = 0;
-fail:
-	__zram_reset_device(zram);
-	pr_err("Initialization failed: err=%d\n", ret);
-	return ret;
 }
 
 static void zram_slot_free_notify(struct block_device *bdev,
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index 5b671d1..2d1a3f1 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -83,11 +83,15 @@ struct zram_stats {
 	u32 bad_compress;	/* % of pages with compression ratio>=75% */
 };
 
-struct zram {
-	struct zs_pool *mem_pool;
+struct zram_meta {
 	void *compress_workmem;
 	void *compress_buffer;
 	struct table *table;
+	struct zs_pool *mem_pool;
+};
+
+struct zram {
+	struct zram_meta *meta;
 	spinlock_t stat64_lock;	/* protect 64-bit stats */
 	struct rw_semaphore lock; /* protect compression buffers and table
 				   * against concurrent read and writes */
@@ -111,7 +115,9 @@ unsigned int zram_get_num_devices(void);
 extern struct attribute_group zram_disk_attr_group;
 #endif
 
-extern int zram_init_device(struct zram *zram);
 extern void zram_reset_device(struct zram *zram);
+extern struct zram_meta *zram_meta_alloc(u64 disksize);
+extern void zram_meta_free(struct zram_meta *meta);
+extern void zram_init_device(struct zram *zram, struct zram_meta *meta);
 
 #endif
diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index 369db12..e6a929d 100644
--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -56,22 +56,26 @@ static ssize_t disksize_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
 	u64 disksize;
+	struct zram_meta *meta;
 	struct zram *zram = dev_to_zram(dev);
 
 	disksize = memparse(buf, NULL);
 	if (!disksize)
 		return -EINVAL;
 
+	disksize = PAGE_ALIGN(disksize);
+	meta = zram_meta_alloc(disksize);
 	down_write(&zram->init_lock);
 	if (zram->init_done) {
 		up_write(&zram->init_lock);
+		zram_meta_free(meta);
 		pr_info("Cannot change disksize for initialized device\n");
 		return -EBUSY;
 	}
 
-	zram->disksize = PAGE_ALIGN(disksize);
+	zram->disksize = disksize;
 	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
-	zram_init_device(zram);
+	zram_init_device(zram, meta);
 	up_write(&zram->init_lock);
 
 	return len;
@@ -182,9 +186,10 @@ static ssize_t mem_used_total_show(struct device *dev,
 {
 	u64 val = 0;
 	struct zram *zram = dev_to_zram(dev);
+	struct zram_meta *meta = zram->meta;
 
 	if (zram->init_done)
-		val = zs_get_total_size_bytes(zram->mem_pool);
+		val = zs_get_total_size_bytes(meta->mem_pool);
 
 	return sprintf(buf, "%llu\n", val);
 }
-- 
1.7.9.5

[PATCH v4 4/4] zram: get rid of lockdep warning

[Minchan Kim]

Lockdep complains about recursive deadlock of zram->init_lock.
[1] in this thread made it false positive because we can't request IO to zram
before setting disksize. Anyway, we should shut lockdep up to
avoid many reporting from user.

[1] zram: force disksize setting before using zram

Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 drivers/staging/zram/zram_drv.c   |  189 +++++++++++++++++++------------------
 drivers/staging/zram/zram_drv.h   |   12 ++-
 drivers/staging/zram/zram_sysfs.c |   11 ++-
 3 files changed, 116 insertions(+), 96 deletions(-)

diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 4264121..0a7fc8d 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -61,22 +61,22 @@ static void zram_stat64_inc(struct zram *zram, u64 *v)
 	zram_stat64_add(zram, v, 1);
 }
 
-static int zram_test_flag(struct zram *zram, u32 index,
+static int zram_test_flag(struct zram_meta *meta, u32 index,
 			enum zram_pageflags flag)
 {
-	return zram->table[index].flags & BIT(flag);
+	return meta->table[index].flags & BIT(flag);
 }
 
-static void zram_set_flag(struct zram *zram, u32 index,
+static void zram_set_flag(struct zram_meta *meta, u32 index,
 			enum zram_pageflags flag)
 {
-	zram->table[index].flags |= BIT(flag);
+	meta->table[index].flags |= BIT(flag);
 }
 
-static void zram_clear_flag(struct zram *zram, u32 index,
+static void zram_clear_flag(struct zram_meta *meta, u32 index,
 			enum zram_pageflags flag)
 {
-	zram->table[index].flags &= ~BIT(flag);
+	meta->table[index].flags &= ~BIT(flag);
 }
 
 static int page_zero_filled(void *ptr)
@@ -96,16 +96,17 @@ static int page_zero_filled(void *ptr)
 
 static void zram_free_page(struct zram *zram, size_t index)
 {
-	unsigned long handle = zram->table[index].handle;
-	u16 size = zram->table[index].size;
+	struct zram_meta *meta = zram->meta;
+	unsigned long handle = meta->table[index].handle;
+	u16 size = meta->table[index].size;
 
 	if (unlikely(!handle)) {
 		/*
 		 * No memory is allocated for zero filled pages.
 		 * Simply clear zero page flag.
 		 */
-		if (zram_test_flag(zram, index, ZRAM_ZERO)) {
-			zram_clear_flag(zram, index, ZRAM_ZERO);
+		if (zram_test_flag(meta, index, ZRAM_ZERO)) {
+			zram_clear_flag(meta, index, ZRAM_ZERO);
 			zram->stats.pages_zero--;
 		}
 		return;
@@ -114,17 +115,17 @@ static void zram_free_page(struct zram *zram, size_t index)
 	if (unlikely(size > max_zpage_size))
 		zram->stats.bad_compress--;
 
-	zs_free(zram->mem_pool, handle);
+	zs_free(meta->mem_pool, handle);
 
 	if (size <= PAGE_SIZE / 2)
 		zram->stats.good_compress--;
 
 	zram_stat64_sub(zram, &zram->stats.compr_size,
-			zram->table[index].size);
+			meta->table[index].size);
 	zram->stats.pages_stored--;
 
-	zram->table[index].handle = 0;
-	zram->table[index].size = 0;
+	meta->table[index].handle = 0;
+	meta->table[index].size = 0;
 }
 
 static void handle_zero_page(struct bio_vec *bvec)
@@ -149,20 +150,21 @@ static int zram_decompress_page(struct zram *zram, char *mem, u32 index)
 	int ret = LZO_E_OK;
 	size_t clen = PAGE_SIZE;
 	unsigned char *cmem;
-	unsigned long handle = zram->table[index].handle;
+	struct zram_meta *meta = zram->meta;
+	unsigned long handle = meta->table[index].handle;
 
-	if (!handle || zram_test_flag(zram, index, ZRAM_ZERO)) {
+	if (!handle || zram_test_flag(meta, index, ZRAM_ZERO)) {
 		memset(mem, 0, PAGE_SIZE);
 		return 0;
 	}
 
-	cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
-	if (zram->table[index].size == PAGE_SIZE)
+	cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_RO);
+	if (meta->table[index].size == PAGE_SIZE)
 		memcpy(mem, cmem, PAGE_SIZE);
 	else
-		ret = lzo1x_decompress_safe(cmem, zram->table[index].size,
+		ret = lzo1x_decompress_safe(cmem, meta->table[index].size,
 						mem, &clen);
-	zs_unmap_object(zram->mem_pool, handle);
+	zs_unmap_object(meta->mem_pool, handle);
 
 	/* Should NEVER happen. Return bio error if it does. */
 	if (unlikely(ret != LZO_E_OK)) {
@@ -180,11 +182,11 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 	int ret;
 	struct page *page;
 	unsigned char *user_mem, *uncmem = NULL;
-
+	struct zram_meta *meta = zram->meta;
 	page = bvec->bv_page;
 
-	if (unlikely(!zram->table[index].handle) ||
-			zram_test_flag(zram, index, ZRAM_ZERO)) {
+	if (unlikely(!meta->table[index].handle) ||
+			zram_test_flag(meta, index, ZRAM_ZERO)) {
 		handle_zero_page(bvec);
 		return 0;
 	}
@@ -231,9 +233,10 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	unsigned long handle;
 	struct page *page;
 	unsigned char *user_mem, *cmem, *src, *uncmem = NULL;
+	struct zram_meta *meta = zram->meta;
 
 	page = bvec->bv_page;
-	src = zram->compress_buffer;
+	src = meta->compress_buffer;
 
 	if (is_partial_io(bvec)) {
 		/*
@@ -255,8 +258,8 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	 * System overwrites unused sectors. Free memory associated
 	 * with this sector now.
 	 */
-	if (zram->table[index].handle ||
-	    zram_test_flag(zram, index, ZRAM_ZERO))
+	if (meta->table[index].handle ||
+	    zram_test_flag(meta, index, ZRAM_ZERO))
 		zram_free_page(zram, index);
 
 	user_mem = kmap_atomic(page);
@@ -274,13 +277,13 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 		if (!is_partial_io(bvec))
 			kunmap_atomic(user_mem);
 		zram->stats.pages_zero++;
-		zram_set_flag(zram, index, ZRAM_ZERO);
+		zram_set_flag(meta, index, ZRAM_ZERO);
 		ret = 0;
 		goto out;
 	}
 
 	ret = lzo1x_1_compress(uncmem, PAGE_SIZE, src, &clen,
-			       zram->compress_workmem);
+			       meta->compress_workmem);
 
 	if (!is_partial_io(bvec)) {
 		kunmap_atomic(user_mem);
@@ -301,14 +304,14 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 			src = uncmem;
 	}
 
-	handle = zs_malloc(zram->mem_pool, clen);
+	handle = zs_malloc(meta->mem_pool, clen);
 	if (!handle) {
 		pr_info("Error allocating memory for compressed "
 			"page: %u, size=%zu\n", index, clen);
 		ret = -ENOMEM;
 		goto out;
 	}
-	cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
+	cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_WO);
 
 	if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
 		src = kmap_atomic(page);
@@ -316,10 +319,10 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 	if ((clen == PAGE_SIZE) && !is_partial_io(bvec))
 		kunmap_atomic(src);
 
-	zs_unmap_object(zram->mem_pool, handle);
+	zs_unmap_object(meta->mem_pool, handle);
 
-	zram->table[index].handle = handle;
-	zram->table[index].size = clen;
+	meta->table[index].handle = handle;
+	meta->table[index].size = clen;
 
 	/* Update stats */
 	zram_stat64_add(zram, &zram->stats.compr_size, clen);
@@ -462,34 +465,25 @@ error:
 void __zram_reset_device(struct zram *zram)
 {
 	size_t index;
+	struct zram_meta *meta;
 
 	if (!zram->init_done)
 		return;
 
+	meta = zram->meta;
 	zram->init_done = 0;
 
-	/* Free various per-device buffers */
-	kfree(zram->compress_workmem);
-	free_pages((unsigned long)zram->compress_buffer, 1);
-
-	zram->compress_workmem = NULL;
-	zram->compress_buffer = NULL;
-
 	/* Free all pages that are still in this zram device */
 	for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
-		unsigned long handle = zram->table[index].handle;
+		unsigned long handle = meta->table[index].handle;
 		if (!handle)
 			continue;
 
-		zs_free(zram->mem_pool, handle);
+		zs_free(meta->mem_pool, handle);
 	}
 
-	vfree(zram->table);
-	zram->table = NULL;
-
-	zs_destroy_pool(zram->mem_pool);
-	zram->mem_pool = NULL;
-
+	zram_meta_free(zram->meta);
+	zram->meta = NULL;
 	/* Reset stats */
 	memset(&zram->stats, 0, sizeof(zram->stats));
 
@@ -504,12 +498,65 @@ void zram_reset_device(struct zram *zram)
 	up_write(&zram->init_lock);
 }
 
-/* zram->init_lock should be held */
-int zram_init_device(struct zram *zram)
+void zram_meta_free(struct zram_meta *meta)
+{
+	zs_destroy_pool(meta->mem_pool);
+	kfree(meta->compress_workmem);
+	free_pages((unsigned long)meta->compress_buffer, 1);
+	vfree(meta->table);
+	kfree(meta);
+}
+
+struct zram_meta *zram_meta_alloc(u64 disksize)
 {
-	int ret;
 	size_t num_pages;
+	struct zram_meta *meta = kmalloc(sizeof(*meta), GFP_KERNEL);
+	if (!meta)
+		goto out;
+
+	meta->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
+	if (!meta->compress_workmem) {
+		pr_err("Error allocating compressor working memory!\n");
+		goto free_meta;
+	}
+
+	meta->compress_buffer =
+		(void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
+	if (!meta->compress_buffer) {
+		pr_err("Error allocating compressor buffer space\n");
+		goto free_workmem;
+	}
+
+	num_pages = disksize >> PAGE_SHIFT;
+	meta->table = vzalloc(num_pages * sizeof(*meta->table));
+	if (!meta->table) {
+		pr_err("Error allocating zram address table\n");
+		goto free_buffer;
+	}
+
+	meta->mem_pool = zs_create_pool("zram", GFP_NOIO | __GFP_HIGHMEM);
+	if (!meta->mem_pool) {
+		pr_err("Error creating memory pool\n");
+		goto free_table;
+	}
+
+	return meta;
+
+free_table:
+	vfree(meta->table);
+free_buffer:
+	free_pages((unsigned long)meta->compress_buffer, 1);
+free_workmem:
+	kfree(meta->compress_workmem);
+free_meta:
+	kfree(meta);
+	meta = NULL;
+out:
+	return meta;
+}
 
+void zram_init_device(struct zram *zram, struct zram_meta *meta)
+{
 	if (zram->disksize > 2 * (totalram_pages << PAGE_SHIFT)) {
 		pr_info(
 		"There is little point creating a zram of greater than "
@@ -524,51 +571,13 @@ int zram_init_device(struct zram *zram)
 		);
 	}
 
-	zram->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
-	if (!zram->compress_workmem) {
-		pr_err("Error allocating compressor working memory!\n");
-		ret = -ENOMEM;
-		goto fail_no_table;
-	}
-
-	zram->compress_buffer =
-		(void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
-	if (!zram->compress_buffer) {
-		pr_err("Error allocating compressor buffer space\n");
-		ret = -ENOMEM;
-		goto fail_no_table;
-	}
-
-	num_pages = zram->disksize >> PAGE_SHIFT;
-	zram->table = vzalloc(num_pages * sizeof(*zram->table));
-	if (!zram->table) {
-		pr_err("Error allocating zram address table\n");
-		ret = -ENOMEM;
-		goto fail_no_table;
-	}
-
 	/* zram devices sort of resembles non-rotational disks */
 	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);
 
-	zram->mem_pool = zs_create_pool("zram", GFP_NOIO | __GFP_HIGHMEM);
-	if (!zram->mem_pool) {
-		pr_err("Error creating memory pool\n");
-		ret = -ENOMEM;
-		goto fail;
-	}
-
+	zram->meta = meta;
 	zram->init_done = 1;
 
 	pr_debug("Initialization done!\n");
-	return 0;
-
-fail_no_table:
-	/* To prevent accessing table entries during cleanup */
-	zram->disksize = 0;
-fail:
-	__zram_reset_device(zram);
-	pr_err("Initialization failed: err=%d\n", ret);
-	return ret;
 }
 
 static void zram_slot_free_notify(struct block_device *bdev,
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index 5b671d1..2d1a3f1 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -83,11 +83,15 @@ struct zram_stats {
 	u32 bad_compress;	/* % of pages with compression ratio>=75% */
 };
 
-struct zram {
-	struct zs_pool *mem_pool;
+struct zram_meta {
 	void *compress_workmem;
 	void *compress_buffer;
 	struct table *table;
+	struct zs_pool *mem_pool;
+};
+
+struct zram {
+	struct zram_meta *meta;
 	spinlock_t stat64_lock;	/* protect 64-bit stats */
 	struct rw_semaphore lock; /* protect compression buffers and table
 				   * against concurrent read and writes */
@@ -111,7 +115,9 @@ unsigned int zram_get_num_devices(void);
 extern struct attribute_group zram_disk_attr_group;
 #endif
 
-extern int zram_init_device(struct zram *zram);
 extern void zram_reset_device(struct zram *zram);
+extern struct zram_meta *zram_meta_alloc(u64 disksize);
+extern void zram_meta_free(struct zram_meta *meta);
+extern void zram_init_device(struct zram *zram, struct zram_meta *meta);
 
 #endif
diff --git a/drivers/staging/zram/zram_sysfs.c b/drivers/staging/zram/zram_sysfs.c
index 369db12..e6a929d 100644
--- a/drivers/staging/zram/zram_sysfs.c
+++ b/drivers/staging/zram/zram_sysfs.c
@@ -56,22 +56,26 @@ static ssize_t disksize_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
 	u64 disksize;
+	struct zram_meta *meta;
 	struct zram *zram = dev_to_zram(dev);
 
 	disksize = memparse(buf, NULL);
 	if (!disksize)
 		return -EINVAL;
 
+	disksize = PAGE_ALIGN(disksize);
+	meta = zram_meta_alloc(disksize);
 	down_write(&zram->init_lock);
 	if (zram->init_done) {
 		up_write(&zram->init_lock);
+		zram_meta_free(meta);
 		pr_info("Cannot change disksize for initialized device\n");
 		return -EBUSY;
 	}
 
-	zram->disksize = PAGE_ALIGN(disksize);
+	zram->disksize = disksize;
 	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
-	zram_init_device(zram);
+	zram_init_device(zram, meta);
 	up_write(&zram->init_lock);
 
 	return len;
@@ -182,9 +186,10 @@ static ssize_t mem_used_total_show(struct device *dev,
 {
 	u64 val = 0;
 	struct zram *zram = dev_to_zram(dev);
+	struct zram_meta *meta = zram->meta;
 
 	if (zram->init_done)
-		val = zs_get_total_size_bytes(zram->mem_pool);
+		val = zs_get_total_size_bytes(meta->mem_pool);
 
 	return sprintf(buf, "%llu\n", val);
 }
-- 
1.7.9.5

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Re: [PATCH v4 1/4] zram: Fix deadlock bug in partial write

[Jerome Marchand]

On 01/22/2013 01:07 AM, Minchan Kim wrote:
> Now zram allocates new page with GFP_KERNEL in zram I/O path
> if IO is partial. Unfortunately, It may cuase deadlock with
> reclaim path so this patch solves the problem.
> 
> Cc: Nitin Gupta <ngupta@vflare.org>
> Cc: Jerome Marchand <jmarchan@redhat.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> 
> We could use GFP_IO instead of GFP_ATOMIC in zram_bvec_read with
> some modification related to buffer allocation in case of partial IO.
> But it needs more churn and prevent merge this patch into stable
> if we should send this to stable so I'd like to keep it as simple
> as possbile. GFP_IO usage could be separate patch after we merge it.
> Thanks.

I'd rather have a preallocated buffer for that. It would make
zram_bvec_read/write() simpler (no need to deal with an allocation
failure or to free the buffer) and it would be consistent with the way
other similar buffer works (compress_workmem/buffer).

Jerome

> 
>  drivers/staging/zram/zram_drv.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 61fb8f1..b285b3a 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -220,7 +220,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
>  	user_mem = kmap_atomic(page);
>  	if (is_partial_io(bvec))
>  		/* Use  a temporary buffer to decompress the page */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +		uncmem = kmalloc(PAGE_SIZE, GFP_ATOMIC);
>  	else
>  		uncmem = user_mem;
>  
> @@ -268,7 +268,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>  		 * This is a partial IO. We need to read the full page
>  		 * before to write the changes.
>  		 */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
>  		if (!uncmem) {
>  			pr_info("Error allocating temp memory!\n");
>  			ret = -ENOMEM;
> 

Re: [PATCH v4 1/4] zram: Fix deadlock bug in partial write

[Jerome Marchand]

On 01/22/2013 01:07 AM, Minchan Kim wrote:
> Now zram allocates new page with GFP_KERNEL in zram I/O path
> if IO is partial. Unfortunately, It may cuase deadlock with
> reclaim path so this patch solves the problem.
> 
> Cc: Nitin Gupta <ngupta@vflare.org>
> Cc: Jerome Marchand <jmarchan@redhat.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> 
> We could use GFP_IO instead of GFP_ATOMIC in zram_bvec_read with
> some modification related to buffer allocation in case of partial IO.
> But it needs more churn and prevent merge this patch into stable
> if we should send this to stable so I'd like to keep it as simple
> as possbile. GFP_IO usage could be separate patch after we merge it.
> Thanks.

I'd rather have a preallocated buffer for that. It would make
zram_bvec_read/write() simpler (no need to deal with an allocation
failure or to free the buffer) and it would be consistent with the way
other similar buffer works (compress_workmem/buffer).

Jerome

> 
>  drivers/staging/zram/zram_drv.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 61fb8f1..b285b3a 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -220,7 +220,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
>  	user_mem = kmap_atomic(page);
>  	if (is_partial_io(bvec))
>  		/* Use  a temporary buffer to decompress the page */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +		uncmem = kmalloc(PAGE_SIZE, GFP_ATOMIC);
>  	else
>  		uncmem = user_mem;
>  
> @@ -268,7 +268,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>  		 * This is a partial IO. We need to read the full page
>  		 * before to write the changes.
>  		 */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
>  		if (!uncmem) {
>  			pr_info("Error allocating temp memory!\n");
>  			ret = -ENOMEM;
> 

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Re: [PATCH v4 1/4] zram: Fix deadlock bug in partial write

[Minchan Kim]

On Tue, Jan 22, 2013 at 10:47:17AM +0100, Jerome Marchand wrote:
> On 01/22/2013 01:07 AM, Minchan Kim wrote:
> > Now zram allocates new page with GFP_KERNEL in zram I/O path
> > if IO is partial. Unfortunately, It may cuase deadlock with
> > reclaim path so this patch solves the problem.
> > 
> > Cc: Nitin Gupta <ngupta@vflare.org>
> > Cc: Jerome Marchand <jmarchan@redhat.com>
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> > 
> > We could use GFP_IO instead of GFP_ATOMIC in zram_bvec_read with
> > some modification related to buffer allocation in case of partial IO.
> > But it needs more churn and prevent merge this patch into stable
> > if we should send this to stable so I'd like to keep it as simple
> > as possbile. GFP_IO usage could be separate patch after we merge it.
> > Thanks.
> 
> I'd rather have a preallocated buffer for that. It would make
> zram_bvec_read/write() simpler (no need to deal with an allocation
> failure or to free the buffer) and it would be consistent with the way
> other similar buffer works (compress_workmem/buffer).

Consistent? Other buffers are MUST for zram working while the buffer
for partial I/O is supplement. Although partial I/O might be common in your config,
it doesn't match with my usecase. I didn't see any partial IO in my usecase.
Nontheless, why should I pay free 4K? Because of just making code SIMPLE?
I don't think current alloc/free handling about partial I/O is mess at the cost
of 4K. And we could use a few zram(a swap and a 2-compressed tmpfs) in system
so the cost is n*4K. Please keep in mind that ZRAM's goal is memory efficiency
and have used in many embedded system which they are always trying to save
just hundred byte.

> 
> Jerome
> 
> > 
> >  drivers/staging/zram/zram_drv.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> > index 61fb8f1..b285b3a 100644
> > --- a/drivers/staging/zram/zram_drv.c
> > +++ b/drivers/staging/zram/zram_drv.c
> > @@ -220,7 +220,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
> >  	user_mem = kmap_atomic(page);
> >  	if (is_partial_io(bvec))
> >  		/* Use  a temporary buffer to decompress the page */
> > -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> > +		uncmem = kmalloc(PAGE_SIZE, GFP_ATOMIC);
> >  	else
> >  		uncmem = user_mem;
> >  
> > @@ -268,7 +268,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> >  		 * This is a partial IO. We need to read the full page
> >  		 * before to write the changes.
> >  		 */
> > -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> > +		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
> >  		if (!uncmem) {
> >  			pr_info("Error allocating temp memory!\n");
> >  			ret = -ENOMEM;
> > 
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
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-- 
Kind regards,
Minchan Kim

Re: [PATCH v4 1/4] zram: Fix deadlock bug in partial write

[Minchan Kim]

On Tue, Jan 22, 2013 at 10:47:17AM +0100, Jerome Marchand wrote:
> On 01/22/2013 01:07 AM, Minchan Kim wrote:
> > Now zram allocates new page with GFP_KERNEL in zram I/O path
> > if IO is partial. Unfortunately, It may cuase deadlock with
> > reclaim path so this patch solves the problem.
> > 
> > Cc: Nitin Gupta <ngupta@vflare.org>
> > Cc: Jerome Marchand <jmarchan@redhat.com>
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> > 
> > We could use GFP_IO instead of GFP_ATOMIC in zram_bvec_read with
> > some modification related to buffer allocation in case of partial IO.
> > But it needs more churn and prevent merge this patch into stable
> > if we should send this to stable so I'd like to keep it as simple
> > as possbile. GFP_IO usage could be separate patch after we merge it.
> > Thanks.
> 
> I'd rather have a preallocated buffer for that. It would make
> zram_bvec_read/write() simpler (no need to deal with an allocation
> failure or to free the buffer) and it would be consistent with the way
> other similar buffer works (compress_workmem/buffer).

Consistent? Other buffers are MUST for zram working while the buffer
for partial I/O is supplement. Although partial I/O might be common in your config,
it doesn't match with my usecase. I didn't see any partial IO in my usecase.
Nontheless, why should I pay free 4K? Because of just making code SIMPLE?
I don't think current alloc/free handling about partial I/O is mess at the cost
of 4K. And we could use a few zram(a swap and a 2-compressed tmpfs) in system
so the cost is n*4K. Please keep in mind that ZRAM's goal is memory efficiency
and have used in many embedded system which they are always trying to save
just hundred byte.

> 
> Jerome
> 
> > 
> >  drivers/staging/zram/zram_drv.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> > index 61fb8f1..b285b3a 100644
> > --- a/drivers/staging/zram/zram_drv.c
> > +++ b/drivers/staging/zram/zram_drv.c
> > @@ -220,7 +220,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
> >  	user_mem = kmap_atomic(page);
> >  	if (is_partial_io(bvec))
> >  		/* Use  a temporary buffer to decompress the page */
> > -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> > +		uncmem = kmalloc(PAGE_SIZE, GFP_ATOMIC);
> >  	else
> >  		uncmem = user_mem;
> >  
> > @@ -268,7 +268,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
> >  		 * This is a partial IO. We need to read the full page
> >  		 * before to write the changes.
> >  		 */
> > -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> > +		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
> >  		if (!uncmem) {
> >  			pr_info("Error allocating temp memory!\n");
> >  			ret = -ENOMEM;
> > 
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
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> see: http://www.linux-mm.org/ .
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-- 
Kind regards,
Minchan Kim

--
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Re: [PATCH v4 1/4] zram: Fix deadlock bug in partial write

[Nitin Gupta]

On 01/21/2013 04:07 PM, Minchan Kim wrote:
> Now zram allocates new page with GFP_KERNEL in zram I/O path
> if IO is partial. Unfortunately, It may cuase deadlock with
> reclaim path so this patch solves the problem.
>
> Cc: Nitin Gupta <ngupta@vflare.org>
> Cc: Jerome Marchand <jmarchan@redhat.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>

For the entire series:
Acked-by: Nitin Gupta <ngupta@vflare.org>


> We could use GFP_IO instead of GFP_ATOMIC in zram_bvec_read with
> some modification related to buffer allocation in case of partial IO.
> But it needs more churn and prevent merge this patch into stable
> if we should send this to stable so I'd like to keep it as simple
> as possbile. GFP_IO usage could be separate patch after we merge it.
> Thanks.
>
>   drivers/staging/zram/zram_drv.c |    4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 61fb8f1..b285b3a 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -220,7 +220,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
>   	user_mem = kmap_atomic(page);
>   	if (is_partial_io(bvec))
>   		/* Use  a temporary buffer to decompress the page */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +		uncmem = kmalloc(PAGE_SIZE, GFP_ATOMIC);
>   	else
>   		uncmem = user_mem;
>
> @@ -268,7 +268,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>   		 * This is a partial IO. We need to read the full page
>   		 * before to write the changes.
>   		 */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
>   		if (!uncmem) {
>   			pr_info("Error allocating temp memory!\n");
>   			ret = -ENOMEM;
>

Re: [PATCH v4 1/4] zram: Fix deadlock bug in partial write

[Nitin Gupta]

On 01/21/2013 04:07 PM, Minchan Kim wrote:
> Now zram allocates new page with GFP_KERNEL in zram I/O path
> if IO is partial. Unfortunately, It may cuase deadlock with
> reclaim path so this patch solves the problem.
>
> Cc: Nitin Gupta <ngupta@vflare.org>
> Cc: Jerome Marchand <jmarchan@redhat.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>

For the entire series:
Acked-by: Nitin Gupta <ngupta@vflare.org>


> We could use GFP_IO instead of GFP_ATOMIC in zram_bvec_read with
> some modification related to buffer allocation in case of partial IO.
> But it needs more churn and prevent merge this patch into stable
> if we should send this to stable so I'd like to keep it as simple
> as possbile. GFP_IO usage could be separate patch after we merge it.
> Thanks.
>
>   drivers/staging/zram/zram_drv.c |    4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> index 61fb8f1..b285b3a 100644
> --- a/drivers/staging/zram/zram_drv.c
> +++ b/drivers/staging/zram/zram_drv.c
> @@ -220,7 +220,7 @@ static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
>   	user_mem = kmap_atomic(page);
>   	if (is_partial_io(bvec))
>   		/* Use  a temporary buffer to decompress the page */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +		uncmem = kmalloc(PAGE_SIZE, GFP_ATOMIC);
>   	else
>   		uncmem = user_mem;
>
> @@ -268,7 +268,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
>   		 * This is a partial IO. We need to read the full page
>   		 * before to write the changes.
>   		 */
> -		uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +		uncmem = kmalloc(PAGE_SIZE, GFP_NOIO);
>   		if (!uncmem) {
>   			pr_info("Error allocating temp memory!\n");
>   			ret = -ENOMEM;
>

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