461a8eee6a
Normally, zram user could get maximum memory usage zram consumed via polling mem_used_total with sysfs in userspace. But it has a critical problem because user can miss peak memory usage during update inverval of polling. For avoiding that, user should poll it with shorter interval(ie, 0.0000000001s) with mlocking to avoid page fault delay when memory pressure is heavy. It would be troublesome. This patch adds new knob "mem_used_max" so user could see the maximum memory usage easily via reading the knob and reset it via "echo 0 > /sys/block/zram0/mem_used_max". Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Dan Streetman <ddstreet@ieee.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Jerome Marchand <jmarchan@redhat.com> Cc: <juno.choi@lge.com> Cc: <seungho1.park@lge.com> Cc: Luigi Semenzato <semenzato@google.com> Cc: Nitin Gupta <ngupta@vflare.org> Cc: Seth Jennings <sjennings@variantweb.net> Reviewed-by: David Horner <ds2horner@gmail.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
131 lines
4.1 KiB
Plaintext
131 lines
4.1 KiB
Plaintext
zram: Compressed RAM based block devices
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----------------------------------------
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* Introduction
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The zram module creates RAM based block devices named /dev/zram<id>
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(<id> = 0, 1, ...). Pages written to these disks are compressed and stored
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in memory itself. These disks allow very fast I/O and compression provides
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good amounts of memory savings. Some of the usecases include /tmp storage,
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use as swap disks, various caches under /var and maybe many more :)
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Statistics for individual zram devices are exported through sysfs nodes at
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/sys/block/zram<id>/
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* Usage
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Following shows a typical sequence of steps for using zram.
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1) Load Module:
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modprobe zram num_devices=4
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This creates 4 devices: /dev/zram{0,1,2,3}
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(num_devices parameter is optional. Default: 1)
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2) Set max number of compression streams
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Compression backend may use up to max_comp_streams compression streams,
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thus allowing up to max_comp_streams concurrent compression operations.
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By default, compression backend uses single compression stream.
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Examples:
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#show max compression streams number
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cat /sys/block/zram0/max_comp_streams
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#set max compression streams number to 3
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echo 3 > /sys/block/zram0/max_comp_streams
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Note:
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In order to enable compression backend's multi stream support max_comp_streams
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must be initially set to desired concurrency level before ZRAM device
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initialisation. Once the device initialised as a single stream compression
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backend (max_comp_streams equals to 1), you will see error if you try to change
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the value of max_comp_streams because single stream compression backend
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implemented as a special case by lock overhead issue and does not support
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dynamic max_comp_streams. Only multi stream backend supports dynamic
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max_comp_streams adjustment.
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3) Select compression algorithm
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Using comp_algorithm device attribute one can see available and
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currently selected (shown in square brackets) compression algortithms,
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change selected compression algorithm (once the device is initialised
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there is no way to change compression algorithm).
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Examples:
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#show supported compression algorithms
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cat /sys/block/zram0/comp_algorithm
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lzo [lz4]
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#select lzo compression algorithm
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echo lzo > /sys/block/zram0/comp_algorithm
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4) Set Disksize
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Set disk size by writing the value to sysfs node 'disksize'.
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The value can be either in bytes or you can use mem suffixes.
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Examples:
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# Initialize /dev/zram0 with 50MB disksize
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echo $((50*1024*1024)) > /sys/block/zram0/disksize
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# Using mem suffixes
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echo 256K > /sys/block/zram0/disksize
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echo 512M > /sys/block/zram0/disksize
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echo 1G > /sys/block/zram0/disksize
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Note:
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There is little point creating a zram of greater than twice the size of memory
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since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
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size of the disk when not in use so a huge zram is wasteful.
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5) Set memory limit: Optional
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Set memory limit by writing the value to sysfs node 'mem_limit'.
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The value can be either in bytes or you can use mem suffixes.
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In addition, you could change the value in runtime.
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Examples:
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# limit /dev/zram0 with 50MB memory
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echo $((50*1024*1024)) > /sys/block/zram0/mem_limit
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# Using mem suffixes
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echo 256K > /sys/block/zram0/mem_limit
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echo 512M > /sys/block/zram0/mem_limit
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echo 1G > /sys/block/zram0/mem_limit
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# To disable memory limit
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echo 0 > /sys/block/zram0/mem_limit
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6) Activate:
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mkswap /dev/zram0
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swapon /dev/zram0
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mkfs.ext4 /dev/zram1
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mount /dev/zram1 /tmp
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7) Stats:
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Per-device statistics are exported as various nodes under
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/sys/block/zram<id>/
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disksize
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num_reads
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num_writes
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failed_reads
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failed_writes
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invalid_io
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notify_free
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zero_pages
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orig_data_size
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compr_data_size
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mem_used_total
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mem_used_max
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8) Deactivate:
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swapoff /dev/zram0
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umount /dev/zram1
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9) Reset:
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Write any positive value to 'reset' sysfs node
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echo 1 > /sys/block/zram0/reset
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echo 1 > /sys/block/zram1/reset
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This frees all the memory allocated for the given device and
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resets the disksize to zero. You must set the disksize again
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before reusing the device.
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Nitin Gupta
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ngupta@vflare.org
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