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authorMinchan Kim <minchan@kernel.org>2019-01-08 15:22:53 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-01-08 17:15:10 -0800
commit1d69a3f8ae77e3dbfdc1356225cce5ea9c366aec (patch)
tree6e070457b08c54a2ed09d66c81ecc8227e7d4e9b /Documentation/blockdev
parent3bd6e94bec122a951d462c239b47954cf5f36e33 (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')
-rw-r--r--Documentation/blockdev/zram.txt74
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