Commit 9b9913d8 authored by Nitin Gupta's avatar Nitin Gupta Committed by Greg Kroah-Hartman
Browse files

Staging: zram: Update zram documentation 



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

Signed-off-by: default avatarNitin Gupta <ngupta@vflare.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 484875ad

drivers/staging/zram/zram.txt

+36 −22
Original line number Diff line number Diff line
@@ -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.



	# Initialize /dev/zram0 with 50MB disksize

	echo $((50*1024*1024)) > /sys/block/zram0/disksize



	*See zramconfig man page for more details and examples*

	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: