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Linux kernel mirror (for testing)
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linux
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
27 Set disk size by writing the value to sysfs node 'disksize'.
28 The value can be either in bytes or you can use mem suffixes.
29 Examples:
30 # Initialize /dev/zram0 with 50MB disksize
31 echo $((50*1024*1024)) > /sys/block/zram0/disksize
32
33 # Using mem suffixes
34 echo 256K > /sys/block/zram0/disksize
35 echo 512M > /sys/block/zram0/disksize
36 echo 1G > /sys/block/zram0/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 and
69 resets the disksize to zero. You must set the disksize again
70 before reusing the device.
71
72Please report any problems at:
73 - Mailing list: linux-mm-cc at laptop dot org
74 - Issue tracker: http://code.google.com/p/compcache/issues/list
75
76Nitin Gupta
77ngupta@vflare.org