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