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Diffstat (limited to 'Documentation/blockdev/zram.txt')
| -rw-r--r-- | Documentation/blockdev/zram.txt | 116 |
1 files changed, 97 insertions, 19 deletions
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt index 7fcf9c6592ec..c4de576093af 100644 --- a/Documentation/blockdev/zram.txt +++ b/Documentation/blockdev/zram.txt @@ -19,7 +19,9 @@ Following shows a typical sequence of steps for using zram. 1) Load Module: modprobe zram num_devices=4 This creates 4 devices: /dev/zram{0,1,2,3} - (num_devices parameter is optional. Default: 1) + +num_devices parameter is optional and tells zram how many devices should be +pre-created. Default: 1. 2) Set max number of compression streams Compression backend may use up to max_comp_streams compression streams, @@ -97,27 +99,103 @@ size of the disk when not in use so a huge zram is wasteful. mkfs.ext4 /dev/zram1 mount /dev/zram1 /tmp -7) 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 - zero_pages - orig_data_size - compr_data_size - mem_used_total - mem_used_max - -8) Deactivate: +7) Add/remove zram devices + +zram provides a control interface, which enables dynamic (on-demand) device +addition and removal. + +In order to add a new /dev/zramX device, perform read operation on hot_add +attribute. This will return either new device's device id (meaning that you +can use /dev/zram<id>) or error code. + +Example: + cat /sys/class/zram-control/hot_add + 1 + +To remove the existing /dev/zramX device (where X is a device id) +execute + echo X > /sys/class/zram-control/hot_remove + +8) Stats: +Per-device statistics are exported as various nodes under /sys/block/zram<id>/ + +A brief description of exported device attritbutes. 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 +num_reads RO the number of reads +failed_reads RO the number of failed reads +num_write RO the number of writes +failed_writes RO the number of failed writes +invalid_io RO the number of non-page-size-aligned I/O requests +max_comp_streams RW the number of possible concurrent compress operations +comp_algorithm RW show and change the compression algorithm +notify_free RO the number of notifications to free pages (either + slot free notifications or REQ_DISCARD requests) +zero_pages RO the number of zero filled pages written to this disk +orig_data_size RO uncompressed size of data stored in this disk +compr_data_size RO compressed size of data stored in this disk +mem_used_total RO the amount of memory allocated for this disk +mem_used_max RW the maximum amount memory zram have consumed to + store compressed data +mem_limit RW the maximum amount of memory ZRAM can use to store + the compressed data +num_migrated RO the number of objects migrated migrated by compaction +compact WO trigger memory compaction + +WARNING +======= +per-stat sysfs attributes are considered to be deprecated. +The basic strategy is: +-- the existing RW nodes will be downgraded to WO nodes (in linux 4.11) +-- deprecated RO sysfs nodes will eventually be removed (in linux 4.11) + +The list of deprecated attributes can be found here: +Documentation/ABI/obsolete/sysfs-block-zram + +Basically, every attribute that has its own read accessible sysfs node +(e.g. num_reads) *AND* is accessible via one of the stat files (zram<id>/stat +or zram<id>/io_stat or zram<id>/mm_stat) is considered to be deprecated. + +User space is advised to use the following files to read the device statistics. + +File /sys/block/zram<id>/stat + +Represents block layer statistics. Read Documentation/block/stat.txt for +details. + +File /sys/block/zram<id>/io_stat + +The stat file represents device's I/O statistics not accounted by block +layer and, thus, not available in zram<id>/stat file. It consists of a +single line of text and contains the following stats separated by +whitespace: + failed_reads + failed_writes + invalid_io + notify_free + +File /sys/block/zram<id>/mm_stat + +The stat file represents device's mm statistics. It consists of a single +line of text and contains the following stats separated by whitespace: + orig_data_size + compr_data_size + mem_used_total + mem_limit + mem_used_max + zero_pages + num_migrated + +9) Deactivate: swapoff /dev/zram0 umount /dev/zram1 -9) Reset: +10) Reset: Write any positive value to 'reset' sysfs node echo 1 > /sys/block/zram0/reset echo 1 > /sys/block/zram1/reset |