drivers/staging/zram/zram.txt

   1 zram: Compressed RAM based block devices
   2 ----------------------------------------
   3
   4 Project home: http://compcache.googlecode.com/
   5
   6 * Introduction
   7
   8 The zram module creates RAM based block devices named /dev/zram<id>
   9 (<id> = 0, 1, ...). Pages written to these disks are compressed and stored
  10 in memory itself. These disks allow very fast I/O and compression provides
  11 good amounts of memory savings. Some of the usecases include /tmp storage,
  12 use as swap disks, various caches under /var and maybe many more :)
  13
  14 Statistics for individual zram devices are exported through sysfs nodes at
  15 /sys/block/zram<id>/
  16
  17 * Usage
  18
  19 Following shows a typical sequence of steps for using zram.
  20
  21 1) 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
  26 2) 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
  38 3) Activate:
  39         mkswap /dev/zram0
  40         swapon /dev/zram0
  41
  42         mkfs.ext4 /dev/zram1
  43         mount /dev/zram1 /tmp
  44
  45 4) 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
  59 5) Deactivate:
  60         swapoff /dev/zram0
  61         umount /dev/zram1
  62
  63 6) 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
  72 Please 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
  76 Nitin Gupta
  77 ngupta@vflare.org