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Staging: zram: Update zram documentation 

Update zram documentation to reflect transition form
ioctl to sysfs interface.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Nitin Gupta 2010-08-09 22:56:55 +05:30 committed by Greg Kroah-Hartman
parent 484875adbc
commit 9b9913d80b
1 changed files with 36 additions and 22 deletions
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58
drivers/staging/zram/zram.txt
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@ -5,33 +5,35 @@ Project home: http://compcache.googlecode.com/
* Introduction
The zram module creates RAM based block devices: /dev/ramX (X = 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.
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 :)
See project home for use cases, performance numbers and a lot more.
Individual zram devices are configured and initialized using zramconfig
userspace utility as shown in examples below. See zramconfig man page for
more details.
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 Modules:
1) Load Module:
modprobe zram num_devices=4
This creates 4 (uninitialized) devices: /dev/zram{0,1,2,3}
This creates 4 devices: /dev/zram{0,1,2,3}
(num_devices parameter is optional. Default: 1)
2) Initialize:
Use zramconfig utility to configure and initialize individual
zram devices. For example:
zramconfig /dev/zram0 --init # uses default value of disksize_kb
zramconfig /dev/zram1 --disksize_kb=102400 # 100MB /dev/zram1
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.
*See zramconfig man page for more details and examples*
# 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
@ -41,17 +43,29 @@ Following shows a typical sequence of steps for using zram.
mount /dev/zram1 /tmp
4) Stats:
zramconfig /dev/zram0 --stats
zramconfig /dev/zram1 --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:
zramconfig /dev/zram0 --reset
zramconfig /dev/zram1 --reset
(This frees memory allocated for the given device).
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: