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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 (Optional):
Set disk size by writing the value to sysfs node 'disksize'
(in bytes). If disksize is not given, default value of 25%
of RAM is used.
# Initialize /dev/zram0 with 50MB disksize
echo $((50*1024*1024)) > /sys/block/zram0/disksize
NOTE: disksize cannot be changed if the disk contains any
data. So, for such a disk, you need to issue 'reset' (see below)
before you can change its 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).
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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