1zram: Compressed RAM based block devices
 2----------------------------------------
 3
 4Project home: http://compcache.googlecode.com/
 5
 6* Introduction
 7
 8The zram module creates RAM based block devices named /dev/zram<id>
 9(<id> = 0, 1, ...). Pages written to these disks are compressed and stored
10in memory itself. These disks allow very fast I/O and compression provides
11good amounts of memory savings. Some of the usecases include /tmp storage,
12use as swap disks, various caches under /var and maybe many more :)
13
14Statistics for individual zram devices are exported through sysfs nodes at
15/sys/block/zram<id>/
16
17* Usage
18
19Following shows a typical sequence of steps for using zram.
20
211) Load Module:
22	modprobe zram num_devices=4
23	This creates 4 devices: /dev/zram{0,1,2,3}
24	(num_devices parameter is optional. Default: 1)
25
262) Set Disksize (Optional):
27	Set disk size by writing the value to sysfs node 'disksize'
28	(in bytes). If disksize is not given, default value of 25%
29	of RAM is used.
30
31	# Initialize /dev/zram0 with 50MB disksize
32	echo $((50*1024*1024)) > /sys/block/zram0/disksize
33
34	NOTE: disksize cannot be changed if the disk contains any
35	data. So, for such a disk, you need to issue 'reset' (see below)
36	before you can change its disksize.
37
383) Activate:
39	mkswap /dev/zram0
40	swapon /dev/zram0
41
42	mkfs.ext4 /dev/zram1
43	mount /dev/zram1 /tmp
44
454) Stats:
46	Per-device statistics are exported as various nodes under
47	/sys/block/zram<id>/
48		disksize
49		num_reads
50		num_writes
51		invalid_io
52		notify_free
53		discard
54		zero_pages
55		orig_data_size
56		compr_data_size
57		mem_used_total
58
595) Deactivate:
60	swapoff /dev/zram0
61	umount /dev/zram1
62
636) Reset:
64	Write any positive value to 'reset' sysfs node
65	echo 1 > /sys/block/zram0/reset
66	echo 1 > /sys/block/zram1/reset
67
68	(This frees all the memory allocated for the given device).
69
70
71Please report any problems at:
72 - Mailing list: linux-mm-cc at laptop dot org
73 - Issue tracker: http://code.google.com/p/compcache/issues/list
74
75Nitin Gupta
76ngupta@vflare.org