[PATCH 09/10] Update zram documentation

Nitin Gupta
2010-08-09T17:27:39Z

Update zram documentation to reflect transition form
ioctl to sysfs interface.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
---
drivers/staging/zram/zram.txt | 58 +++++++++++++++++++++++++---------------
1 files changed, 36 insertions(+), 22 deletions(-)

diff --git a/drivers/staging/zram/zram.txt b/drivers/staging/zram/zram.txt
index 520edc1..5f75d29 100644
--- a/drivers/staging/zram/zram.txt
+++ b/drivers/staging/zram/zram.txt
@@ -5,33 +5,35 @@ Project home: http://compcache.googlecode.com/

* Introduction

-The zram module creates RAM based block devices: /dev/ramX (X = 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.
+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 :)

-See project home for use cases, performance numbers and a lot more.
-
-Individual zram devices are configured and initialized using zramconfig
-userspace utility as shown in examples below. See zramconfig man page for
-more details.
+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 Modules:
+1) Load Module:
modprobe zram num_devices=4
- This creates 4 (uninitialized) devices: /dev/zram{0,1,2,3}
+ This creates 4 devices: /dev/zram{0,1,2,3}
(num_devices parameter is optional. Default: 1)

-2) Initialize:
- Use zramconfig utility to configure and initialize individual
- zram devices. For example:
- zramconfig /dev/zram0 --init # uses default value of disksize_kb
- zramconfig /dev/zram1 --disksize_kb=102400 # 100MB /dev/zram1
+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

- *See zramconfig man page for more details and examples*
+ 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
@@ -41,17 +43,29 @@ Following shows a typical sequence of steps for using zram.
mount /dev/zram1 /tmp

4) Stats:
- zramconfig /dev/zram0 --stats
- zramconfig /dev/zram1 --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:
- zramconfig /dev/zram0 --reset
- zramconfig /dev/zram1 --reset
- (This frees memory allocated for the given device).
+ 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:
--
1.7.2.1