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zram: Compressed RAM based block devices
----------------------------------------
Project home: http://compcache.googlecode.com/
* Introduction
The zram module creates RAM based block devices named /dev/zram<id>
(<id> = 0, 1, ...). Pages written to these disks are compressed and stored
in memory itself. These disks allow very fast I/O and compression provides
good amounts of memory savings. Some of the usecases include /tmp storage,
use as swap disks, various caches under /var and maybe many more :)
Statistics for individual zram devices are exported through sysfs nodes at
/sys/block/zram<id>/
* Usage
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)
2) 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:
# Initialize /dev/zram0 with 50MB disksize
echo $((50*1024*1024)) > /sys/block/zram0/disksize
# Using mem suffixes
echo 256K > /sys/block/zram0/disksize
echo 512M > /sys/block/zram0/disksize
echo 1G > /sys/block/zram0/disksize
3) Activate:
mkswap /dev/zram0
swapon /dev/zram0
mkfs.ext4 /dev/zram1
mount /dev/zram1 /tmp
4) Stats:
Per-device statistics are exported as various nodes under
/sys/block/zram<id>/
disksize
num_reads
num_writes
invalid_io
notify_free
discard
zero_pages
orig_data_size
compr_data_size
mem_used_total
5) Deactivate:
swapoff /dev/zram0
umount /dev/zram1
6) Reset:
Write any positive value to 'reset' sysfs node
echo 1 > /sys/block/zram0/reset
echo 1 > /sys/block/zram1/reset
This frees all the memory allocated for the given device and
resets the disksize to zero. You must set the disksize again
before reusing the device.
Please report any problems at:
- Mailing list: linux-mm-cc at laptop dot org
- Issue tracker: http://code.google.com/p/compcache/issues/list
Nitin Gupta
ngupta@vflare.org
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