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authorMinchan Kim <minchan@kernel.org>2018-12-28 11:36:54 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2018-12-28 23:11:49 +0300
commitbb416d18b850faaa44bd3bb67c9728922c3cce98 (patch)
tree112f74c2842e9e2565911546cb0ff69c407ad393 /Documentation/blockdev
parent23eddf39b2c28c05cb8f8203d38e61807d701b38 (diff)
downloadlinux-bb416d18b850faaa44bd3bb67c9728922c3cce98.tar.xz
zram: writeback throttle
If there are lots of write IO with flash device, it could have a wearout problem of storage. To overcome the problem, admin needs to design write limitation to guarantee flash health for entire product life. This patch creates a new knob "writeback_limit" for zram. 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. 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)) > \ /sys/block/zram0/writeback_limit. If admin want to allow further write again, he could do it like below echo 0 > /sys/block/zram0/writeback_limit If admin want to see remaining writeback budget, cat /sys/block/zram0/writeback_limit 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. [minchan@kernel.org: v4] Link: http://lkml.kernel.org/r/20181203024045.153534-8-minchan@kernel.org Link: http://lkml.kernel.org/r/20181127055429.251614-8-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Joey Pabalinas <joeypabalinas@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/blockdev')
-rw-r--r--Documentation/blockdev/zram.txt31
1 files changed, 31 insertions, 0 deletions
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 906df97527a7..436c5e98e1b6 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -164,6 +164,8 @@ reset WO trigger device reset
mem_used_max WO reset the `mem_used_max' counter (see later)
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
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
@@ -275,6 +277,35 @@ Admin can request writeback of those idle pages at right timing via
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.
+
+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)) > \
+ /sys/block/zram0/writeback_limit.
+
+If admin want to allow further write again, he could do it like below
+
+ echo 0 > /sys/block/zram0/writeback_limit
+
+If admin want to see remaining writeback budget since he set,
+
+ cat /sys/block/zram0/writeback_limit
+
+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.
+
= memory tracking
With CONFIG_ZRAM_MEMORY_TRACKING, user can know information of the