summaryrefslogtreecommitdiff
path: root/Documentation/blockdev/zram.txt
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/blockdev/zram.txt')
-rw-r--r--Documentation/blockdev/zram.txt71
1 files changed, 71 insertions, 0 deletions
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
new file mode 100644
index 000000000000..2eccddffa6c8
--- /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