Commit 1d69a3f8 authored by Minchan Kim's avatar Minchan Kim Committed by Linus Torvalds
Browse files

zram: idle writeback fixes and cleanup 

This patch includes some fixes and cleanup for idle-page writeback.

1. writeback_limit interface

Now writeback_limit interface is rather conusing.  For example, once
writeback limit budget is exausted, admin can see 0 from
/sys/block/zramX/writeback_limit which is same semantic with disable
writeback_limit at this moment.  IOW, admin cannot tell that zero came
from disable writeback limit or exausted writeback limit.

To make the interface clear, let's sepatate enable of writeback limit to
another knob - /sys/block/zram0/writeback_limit_enable

* before:
  while true :
    # to re-enable writeback limit once previous one is used up
    echo 0 > /sys/block/zram0/writeback_limit
    echo $((200<<20)) > /sys/block/zram0/writeback_limit
    ..
    .. # used up the writeback limit budget

* new
  # To enable writeback limit, from the beginning, admin should
  # enable it.
  echo $((200<<20)) > /sys/block/zram0/writeback_limit
  echo 1 > /sys/block/zram/0/writeback_limit_enable
  while true :
    echo $((200<<20)) > /sys/block/zram0/writeback_limit
    ..
    .. # used up the writeback limit budget

It's much strightforward.

2. fix condition check idle/huge writeback mode check

The mode in writeback_store is not bit opeartion any more so no need to
use bit operations.  Furthermore, current condition check is broken in
that it does writeback every pages regardless of huge/idle.

3. clean up idle_store

No need to use goto.

[minchan@kernel.org: missed spin_lock_init]
  Link: http://lkml.kernel.org/r/20190103001601.GA255139@google.com
Link: http://lkml.kernel.org/r/20181224033529.19450-1-minchan@kernel.org


Signed-off-by: default avatarMinchan Kim <minchan@kernel.org>
Suggested-by: default avatarJohn Dias <joaodias@google.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: John Dias <joaodias@google.com>
Cc: Srinivas Paladugu <srnvs@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3bd6e94b

Documentation/ABI/testing/sysfs-block-zram

+9 −2
Original line number Diff line number Diff line
@@ -122,11 +122,18 @@ Description: 
		statistics (bd_count, bd_reads, bd_writes) in a format

		similar to block layer statistics file format.



What:		/sys/block/zram<id>/writeback_limit_enable

Date:		November 2018

Contact:	Minchan Kim <minchan@kernel.org>

Description:

		The writeback_limit_enable file is read-write and specifies

		eanbe of writeback_limit feature. "1" means eable the feature.

		No limit "0" is the initial state.



What:		/sys/block/zram<id>/writeback_limit

Date:		November 2018

Contact:	Minchan Kim <minchan@kernel.org>

Description:

		The writeback_limit file is read-write and specifies the maximum

		amount of writeback ZRAM can do. The limit could be changed

		in run time and "0" means disable the limit.

		No limit is the initial state.
 
		in run time.

Documentation/blockdev/zram.txt

+47 −27
Original line number Diff line number Diff line
@@ -166,6 +166,7 @@ mem_limit WO specifies the maximum amount of memory ZRAM can use 
				to store the compressed data

writeback_limit   	WO	specifies the maximum amount of write IO zram can

				write out to backing device as 4KB unit

writeback_limit_enable  RW	show and set writeback_limit feature

max_comp_streams  	RW	the number of possible concurrent compress operations

comp_algorithm    	RW	show and change the compression algorithm

compact           	WO	trigger memory compaction
@@ -280,32 +281,51 @@ With the command, zram writeback idle pages from memory to the storage. 
If there are lots of write IO with flash device, potentially, it has

flash wearout problem so that admin needs to design write limitation

to guarantee storage health for entire product life.

To overcome the concern, zram supports "writeback_limit".

The "writeback_limit"'s default value is 0 so that it doesn't limit

any writeback. If admin want to measure writeback count in a certain

period, he could know it via /sys/block/zram0/bd_stat's 3rd column.



To overcome the concern, zram supports "writeback_limit" feature.

The "writeback_limit_enable"'s default value is 0 so that it doesn't limit

any writeback. IOW, if admin want to apply writeback budget, he should

enable writeback_limit_enable via



	$ echo 1 > /sys/block/zramX/writeback_limit_enable



Once writeback_limit_enable is set, zram doesn't allow any writeback

until admin set the budget via /sys/block/zramX/writeback_limit.



(If admin doesn't enable writeback_limit_enable, writeback_limit's value

assigned via /sys/block/zramX/writeback_limit is meaninless.)



If admin want to limit writeback as per-day 400M, he could do it

like below.



    MB_SHIFT=20

    4K_SHIFT=12

    echo $((400<<MB_SHIFT>>4K_SHIFT)) > \

	$ MB_SHIFT=20

	$ 4K_SHIFT=12

	$ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \

		/sys/block/zram0/writeback_limit.

	$ echo 1 > /sys/block/zram0/writeback_limit_enable



If admin want to allow further write again, he could do it like below

If admin want to allow further write again once the bugdet is exausted,

he could do it like below



    echo 0 > /sys/block/zram0/writeback_limit

	$ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \

		/sys/block/zram0/writeback_limit



If admin want to see remaining writeback budget since he set,



    cat /sys/block/zram0/writeback_limit

	$ cat /sys/block/zramX/writeback_limit



If admin want to disable writeback limit, he could do



	$ echo 0 > /sys/block/zramX/writeback_limit_enable



The writeback_limit count will reset whenever you reset zram(e.g.,

system reboot, echo 1 > /sys/block/zramX/reset) so keeping how many of

writeback happened until you reset the zram to allocate extra writeback

budget in next setting is user's job.



If admin want to measure writeback count in a certain period, he could

know it via /sys/block/zram0/bd_stat's 3rd column.



= memory tracking



With CONFIG_ZRAM_MEMORY_TRACKING, user can know information of the

drivers/block/zram/zram_drv.c

+66 −24
Original line number Diff line number Diff line
@@ -316,11 +316,9 @@ static ssize_t idle_store(struct device *dev, 
		 * See the comment in writeback_store.

		 */

		zram_slot_lock(zram, index);

		if (!zram_allocated(zram, index) ||

				zram_test_flag(zram, index, ZRAM_UNDER_WB))

			goto next;

		if (zram_allocated(zram, index) &&

				!zram_test_flag(zram, index, ZRAM_UNDER_WB))

			zram_set_flag(zram, index, ZRAM_IDLE);

next:

		zram_slot_unlock(zram, index);

	}
@@ -330,6 +328,41 @@ next: 
}



#ifdef CONFIG_ZRAM_WRITEBACK

static ssize_t writeback_limit_enable_store(struct device *dev,

		struct device_attribute *attr, const char *buf, size_t len)

{

	struct zram *zram = dev_to_zram(dev);

	u64 val;

	ssize_t ret = -EINVAL;



	if (kstrtoull(buf, 10, &val))

		return ret;



	down_read(&zram->init_lock);

	spin_lock(&zram->wb_limit_lock);

	zram->wb_limit_enable = val;

	spin_unlock(&zram->wb_limit_lock);

	up_read(&zram->init_lock);

	ret = len;



	return ret;

}



static ssize_t writeback_limit_enable_show(struct device *dev,

		struct device_attribute *attr, char *buf)

{

	bool val;

	struct zram *zram = dev_to_zram(dev);



	down_read(&zram->init_lock);

	spin_lock(&zram->wb_limit_lock);

	val = zram->wb_limit_enable;

	spin_unlock(&zram->wb_limit_lock);

	up_read(&zram->init_lock);



	return scnprintf(buf, PAGE_SIZE, "%d\n", val);

}



static ssize_t writeback_limit_store(struct device *dev,

		struct device_attribute *attr, const char *buf, size_t len)

{
@@ -341,9 +374,9 @@ static ssize_t writeback_limit_store(struct device *dev, 
		return ret;



	down_read(&zram->init_lock);

	atomic64_set(&zram->stats.bd_wb_limit, val);

	if (val == 0)

		zram->stop_writeback = false;

	spin_lock(&zram->wb_limit_lock);

	zram->bd_wb_limit = val;

	spin_unlock(&zram->wb_limit_lock);

	up_read(&zram->init_lock);

	ret = len;
@@ -357,7 +390,9 @@ static ssize_t writeback_limit_show(struct device *dev, 
	struct zram *zram = dev_to_zram(dev);



	down_read(&zram->init_lock);

	val = atomic64_read(&zram->stats.bd_wb_limit);

	spin_lock(&zram->wb_limit_lock);

	val = zram->bd_wb_limit;

	spin_unlock(&zram->wb_limit_lock);

	up_read(&zram->init_lock);



	return scnprintf(buf, PAGE_SIZE, "%llu\n", val);
@@ -588,8 +623,8 @@ static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec, 
	return 1;

}



#define HUGE_WRITEBACK 0x1

#define IDLE_WRITEBACK 0x2

#define HUGE_WRITEBACK 1

#define IDLE_WRITEBACK 2



static ssize_t writeback_store(struct device *dev,

		struct device_attribute *attr, const char *buf, size_t len)
@@ -602,7 +637,7 @@ static ssize_t writeback_store(struct device *dev, 
	struct page *page;

	ssize_t ret, sz;

	char mode_buf[8];

	unsigned long mode = -1UL;

	int mode = -1;

	unsigned long blk_idx = 0;



	sz = strscpy(mode_buf, buf, sizeof(mode_buf));
@@ -618,7 +653,7 @@ static ssize_t writeback_store(struct device *dev, 
	else if (!strcmp(mode_buf, "huge"))

		mode = HUGE_WRITEBACK;



	if (mode == -1UL)

	if (mode == -1)

		return -EINVAL;



	down_read(&zram->init_lock);
@@ -645,10 +680,13 @@ static ssize_t writeback_store(struct device *dev, 
		bvec.bv_len = PAGE_SIZE;

		bvec.bv_offset = 0;



		if (zram->stop_writeback) {

		spin_lock(&zram->wb_limit_lock);

		if (zram->wb_limit_enable && !zram->bd_wb_limit) {

			spin_unlock(&zram->wb_limit_lock);

			ret = -EIO;

			break;

		}

		spin_unlock(&zram->wb_limit_lock);



		if (!blk_idx) {

			blk_idx = alloc_block_bdev(zram);
@@ -667,10 +705,11 @@ static ssize_t writeback_store(struct device *dev, 
				zram_test_flag(zram, index, ZRAM_UNDER_WB))

			goto next;



		if ((mode & IDLE_WRITEBACK &&

			  !zram_test_flag(zram, index, ZRAM_IDLE)) &&

		    (mode & HUGE_WRITEBACK &&

			  !zram_test_flag(zram, index, ZRAM_HUGE)))

		if (mode == IDLE_WRITEBACK &&

			  !zram_test_flag(zram, index, ZRAM_IDLE))

			goto next;

		if (mode == HUGE_WRITEBACK &&

			  !zram_test_flag(zram, index, ZRAM_HUGE))

			goto next;

		/*

		 * Clearing ZRAM_UNDER_WB is duty of caller.
@@ -732,11 +771,10 @@ static ssize_t writeback_store(struct device *dev, 
		zram_set_element(zram, index, blk_idx);

		blk_idx = 0;

		atomic64_inc(&zram->stats.pages_stored);

		if (atomic64_add_unless(&zram->stats.bd_wb_limit,

					-1 << (PAGE_SHIFT - 12), 0)) {

			if (atomic64_read(&zram->stats.bd_wb_limit) == 0)

				zram->stop_writeback = true;

		}

		spin_lock(&zram->wb_limit_lock);

		if (zram->wb_limit_enable && zram->bd_wb_limit > 0)

			zram->bd_wb_limit -=  1UL << (PAGE_SHIFT - 12);

		spin_unlock(&zram->wb_limit_lock);

next:

		zram_slot_unlock(zram, index);

	}
@@ -1812,6 +1850,7 @@ static DEVICE_ATTR_RW(comp_algorithm); 
static DEVICE_ATTR_RW(backing_dev);

static DEVICE_ATTR_WO(writeback);

static DEVICE_ATTR_RW(writeback_limit);

static DEVICE_ATTR_RW(writeback_limit_enable);

#endif



static struct attribute *zram_disk_attrs[] = {
@@ -1828,6 +1867,7 @@ static struct attribute *zram_disk_attrs[] = { 
	&dev_attr_backing_dev.attr,

	&dev_attr_writeback.attr,

	&dev_attr_writeback_limit.attr,

	&dev_attr_writeback_limit_enable.attr,

#endif

	&dev_attr_io_stat.attr,

	&dev_attr_mm_stat.attr,
@@ -1867,7 +1907,9 @@ static int zram_add(void) 
	device_id = ret;



	init_rwsem(&zram->init_lock);



#ifdef CONFIG_ZRAM_WRITEBACK

	spin_lock_init(&zram->wb_limit_lock);

#endif

	queue = blk_alloc_queue(GFP_KERNEL);

	if (!queue) {

		pr_err("Error allocating disk queue for device %d\n",

drivers/block/zram/zram_drv.h

+3 −2
Original line number Diff line number Diff line
@@ -86,7 +86,6 @@ struct zram_stats { 
	atomic64_t bd_count;		/* no. of pages in backing device */

	atomic64_t bd_reads;		/* no. of reads from backing device */

	atomic64_t bd_writes;		/* no. of writes from backing device */

	atomic64_t bd_wb_limit;		/* writeback limit of backing device */

#endif

};
@@ -114,8 +113,10 @@ struct zram { 
	 */

	bool claim; /* Protected by bdev->bd_mutex */

	struct file *backing_dev;

	bool stop_writeback;

#ifdef CONFIG_ZRAM_WRITEBACK

	spinlock_t wb_limit_lock;

	bool wb_limit_enable;

	u64 bd_wb_limit;

	struct block_device *bdev;

	unsigned int old_block_size;

	unsigned long *bitmap;

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