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Diffstat (limited to 'Documentation/blockdev/zram.txt')
| -rw-r--r-- | Documentation/blockdev/zram.txt | 54 |
1 files changed, 48 insertions, 6 deletions
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt index 2eccddffa6c..0595c3f56cc 100644 --- a/Documentation/blockdev/zram.txt +++ b/Documentation/blockdev/zram.txt @@ -21,7 +21,43 @@ Following shows a typical sequence of steps for using zram. This creates 4 devices: /dev/zram{0,1,2,3} (num_devices parameter is optional. Default: 1) -2) Set Disksize +2) Set max number of compression streams + Compression backend may use up to max_comp_streams compression streams, + thus allowing up to max_comp_streams concurrent compression operations. + By default, compression backend uses single compression stream. + + Examples: + #show max compression streams number + cat /sys/block/zram0/max_comp_streams + + #set max compression streams number to 3 + echo 3 > /sys/block/zram0/max_comp_streams + +Note: +In order to enable compression backend's multi stream support max_comp_streams +must be initially set to desired concurrency level before ZRAM device +initialisation. Once the device initialised as a single stream compression +backend (max_comp_streams equals to 1), you will see error if you try to change +the value of max_comp_streams because single stream compression backend +implemented as a special case by lock overhead issue and does not support +dynamic max_comp_streams. Only multi stream backend supports dynamic +max_comp_streams adjustment. + +3) Select compression algorithm + Using comp_algorithm device attribute one can see available and + currently selected (shown in square brackets) compression algortithms, + change selected compression algorithm (once the device is initialised + there is no way to change compression algorithm). + + Examples: + #show supported compression algorithms + cat /sys/block/zram0/comp_algorithm + lzo [lz4] + + #select lzo compression algorithm + echo lzo > /sys/block/zram0/comp_algorithm + +4) Set Disksize Set disk size by writing the value to sysfs node 'disksize'. The value can be either in bytes or you can use mem suffixes. Examples: @@ -33,32 +69,38 @@ Following shows a typical sequence of steps for using zram. echo 512M > /sys/block/zram0/disksize echo 1G > /sys/block/zram0/disksize -3) Activate: +Note: +There is little point creating a zram of greater than twice the size of memory +since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the +size of the disk when not in use so a huge zram is wasteful. + +5) Activate: mkswap /dev/zram0 swapon /dev/zram0 mkfs.ext4 /dev/zram1 mount /dev/zram1 /tmp -4) Stats: +6) Stats: Per-device statistics are exported as various nodes under /sys/block/zram<id>/ disksize num_reads num_writes + failed_reads + failed_writes invalid_io notify_free - discard zero_pages orig_data_size compr_data_size mem_used_total -5) Deactivate: +7) Deactivate: swapoff /dev/zram0 umount /dev/zram1 -6) Reset: +8) Reset: Write any positive value to 'reset' sysfs node echo 1 > /sys/block/zram0/reset echo 1 > /sys/block/zram1/reset |