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diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt new file mode 100644 index 00000000000..2eccddffa6c --- /dev/null +++ b/Documentation/blockdev/zram.txt @@ -0,0 +1,71 @@ +zram: Compressed RAM based block devices +---------------------------------------- + +* 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. + +Nitin Gupta +ngupta@vflare.org |