diff options
Diffstat (limited to 'Documentation/blockdev/zram.txt')
| -rw-r--r-- | Documentation/blockdev/zram.txt | 31 |
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 |