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 (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 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 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). 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