2010-06-01 08:01:26 +00:00
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zram: Compressed RAM based block devices
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2009-09-22 04:56:54 +00:00
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Project home: http://compcache.googlecode.com/
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* Introduction
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2010-08-09 17:26:55 +00:00
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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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2009-09-22 04:56:54 +00:00
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2010-08-09 17:26:55 +00:00
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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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2009-09-22 04:56:54 +00:00
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* Usage
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2010-06-01 08:01:26 +00:00
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Following shows a typical sequence of steps for using zram.
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2009-09-22 04:56:54 +00:00
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2010-08-09 17:26:55 +00:00
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1) Load Module:
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2010-06-01 08:01:26 +00:00
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modprobe zram num_devices=4
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2010-08-09 17:26:55 +00:00
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This creates 4 devices: /dev/zram{0,1,2,3}
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2009-09-22 04:56:54 +00:00
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(num_devices parameter is optional. Default: 1)
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2013-01-30 02:41:40 +00:00
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2) 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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2009-09-22 04:56:54 +00:00
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3) Activate:
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2010-06-01 08:01:26 +00:00
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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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2009-09-22 04:56:54 +00:00
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4) Stats:
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2010-08-09 17:26:55 +00:00
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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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invalid_io
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notify_free
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discard
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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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2009-09-22 04:56:54 +00:00
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5) Deactivate:
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2010-06-01 08:01:26 +00:00
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swapoff /dev/zram0
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umount /dev/zram1
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2009-09-22 04:56:54 +00:00
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6) Reset:
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2010-08-09 17:26:55 +00:00
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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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2013-01-30 02:41:40 +00:00
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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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2009-09-22 04:56:54 +00:00
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Please report any problems at:
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- Mailing list: linux-mm-cc at laptop dot org
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- Issue tracker: http://code.google.com/p/compcache/issues/list
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Nitin Gupta
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ngupta@vflare.org
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