diff options
author | Minchan Kim <minchan@kernel.org> | 2019-01-08 15:22:53 -0800 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-01-08 17:15:10 -0800 |
commit | 1d69a3f8ae77e3dbfdc1356225cce5ea9c366aec (patch) | |
tree | 6e070457b08c54a2ed09d66c81ecc8227e7d4e9b /Documentation/blockdev/zram.txt | |
parent | 3bd6e94bec122a951d462c239b47954cf5f36e33 (diff) |
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: Minchan Kim <minchan@kernel.org>
Suggested-by: John 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/blockdev/zram.txt')
-rw-r--r-- | Documentation/blockdev/zram.txt | 74 |
1 files changed, 47 insertions, 27 deletions
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt index 436c5e98e1b6..4df0ce271085 100644 --- a/Documentation/blockdev/zram.txt +++ b/Documentation/blockdev/zram.txt @@ -156,22 +156,23 @@ Per-device statistics are exported as various nodes under /sys/block/zram<id>/ A brief description of exported device attributes. For more details please read Documentation/ABI/testing/sysfs-block-zram. -Name access description ----- ------ ----------- -disksize RW show and set the device's disk size -initstate RO shows the initialization state of the device -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 -debug_stat RO this file is used for zram debugging purposes -backing_dev RW set up backend storage for zram to write out -idle WO mark allocated slot as idle +Name access description +---- ------ ----------- +disksize RW show and set the device's disk size +initstate RO shows the initialization state of the device +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 +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 +debug_stat RO this file is used for zram debugging purposes +backing_dev RW set up backend storage for zram to write out +idle WO mark allocated slot as idle User space is advised to use the following files to read the device statistics. @@ -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)) > \ - /sys/block/zram0/writeback_limit. + $ 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 |