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zram: update documentation 

Several documentation changes.

First, we never mentioned any errors and never required any
error checks in documentation.

Second, mention that there is another way to configure and
manage zram devices -- zramctl, provided by util-linux.

Third, add a bit of clarification on why `mem_used_max' attr
is RW and correct some typos.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Sergey SENOZHATSKY 2015-09-24 18:56:41 +09:00 committed by Jonathan Corbet
parent 1c0032c8eb
commit 3657c20d82
1 changed files with 40 additions and 4 deletions
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44
Documentation/blockdev/zram.txt
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@ -14,8 +14,43 @@ Statistics for individual zram devices are exported through sysfs nodes at
* Usage
There are several ways to configure and manage zram device(-s):
a) using zram and zram_control sysfs attributes
b) using zramctl utility, provided by util-linux (util-linux@vger.kernel.org).
In this document we will describe only 'manual' zram configuration steps,
IOW, zram and zram_control sysfs attributes.
In order to get a better idea about zramctl please consult util-linux
documentation, zramctl man-page or `zramctl --help'. Please be informed
that zram maintainers do not develop/maintain util-linux or zramctl, should
you have any questions please contact util-linux@vger.kernel.org
Following shows a typical sequence of steps for using zram.
WARNING
=======
For the sake of simplicity we skip error checking parts in most of the
examples below. However, it is your sole responsibility to handle errors.
zram sysfs attributes always return negative values in case of errors.
The list of possible return codes:
-EBUSY -- an attempt to modify an attribute that cannot be changed once
the device has been initialised. Please reset device first;
-ENOMEM -- zram was not able to allocate enough memory to fulfil your
needs;
-EINVAL -- invalid input has been provided.
If you use 'echo', the returned value that is changed by 'echo' utility,
and, in general case, something like:
echo 3 > /sys/block/zram0/max_comp_streams
if [ $? -ne 0 ];
handle_error
fi
should suffice.
1) Load Module:
modprobe zram num_devices=4
This creates 4 devices: /dev/zram{0,1,2,3}
@ -47,7 +82,7 @@ max_comp_streams adjustment.
3) Select compression algorithm
Using comp_algorithm device attribute one can see available and
currently selected (shown in square brackets) compression algortithms,
currently selected (shown in square brackets) compression algorithms,
change selected compression algorithm (once the device is initialised
there is no way to change compression algorithm).
@ -119,7 +154,7 @@ execute
8) Stats:
Per-device statistics are exported as various nodes under /sys/block/zram<id>/
A brief description of exported device attritbutes. For more details please
A brief description of exported device attributes. For more details please
read Documentation/ABI/testing/sysfs-block-zram.
Name access description
@ -140,8 +175,9 @@ zero_pages RO the number of zero filled pages written to this disk
orig_data_size RO uncompressed size of data stored in this disk
compr_data_size RO compressed size of data stored in this disk
mem_used_total RO the amount of memory allocated for this disk
mem_used_max RW the maximum amount memory zram have consumed to
store compressed data
mem_used_max RW the maximum amount of memory zram have consumed to
store the data (to reset this counter to the actual
current value, write 1 to this attribute)
mem_limit RW the maximum amount of memory ZRAM can use to store
the compressed data
pages_compacted RO the number of pages freed during compaction