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Documentation/zram: add documentation for algorithm parameters

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Document brief description of compression algorithms' parameters:
compression level and pre-trained dictionary.

[senozhatsky@chromium.org: trivial fixup]
  Link: https://lkml.kernel.org/r/20240903063722.1603592-1-senozhatsky@chromium.org
Link: https://lkml.kernel.org/r/20240902105656.1383858-24-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nick Terrell <terrelln@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Sergey Senozhatsky 2024-09-02 19:56:11 +09:00 committed by Andrew Morton
parent 6a559ecd6e
commit 97ee4842f2
1 changed files with 39 additions and 8 deletions
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47
Documentation/admin-guide/blockdev/zram.rst
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@ -105,7 +105,38 @@ Examples::
For the time being, the `comp_algorithm` content shows only compression
algorithms that are supported by zram.
4) Set Disksize
4) Set compression algorithm parameters: Optional
=================================================
Compression algorithms may support specific parameters which can be
tweaked for particular dataset. ZRAM has an `algorithm_params` device
attribute which provides a per-algorithm params configuration.
For example, several compression algorithms support `level` parameter.
In addition, certain compression algorithms support pre-trained dictionaries,
which significantly change algorithms' characteristics. In order to configure
compression algorithm to use external pre-trained dictionary, pass full
path to the `dict` along with other parameters::
#pass path to pre-trained zstd dictionary
echo "algo=zstd dict=/etc/dictioary" > /sys/block/zram0/algorithm_params
#same, but using algorithm priority
echo "priority=1 dict=/etc/dictioary" > \
/sys/block/zram0/algorithm_params
#pass path to pre-trained zstd dictionary and compression level
echo "algo=zstd level=8 dict=/etc/dictioary" > \
/sys/block/zram0/algorithm_params
Parameters are algorithm specific: not all algorithms support pre-trained
dictionaries, not all algorithms support `level`. Furthermore, for certain
algorithms `level` controls the compression level (the higher the value the
better the compression ratio, it even can take negatives values for some
algorithms), for other algorithms `level` is acceleration level (the higher
the value the lower the compression ratio).
5) Set Disksize
===============
Set disk size by writing the value to sysfs node 'disksize'.
@ -125,7 +156,7 @@ There is little point creating a zram of greater than twice the size of memory
since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
size of the disk when not in use so a huge zram is wasteful.
5) Set memory limit: Optional
6) Set memory limit: Optional
=============================
Set memory limit by writing the value to sysfs node 'mem_limit'.
@ -144,7 +175,7 @@ Examples::
# To disable memory limit
echo 0 > /sys/block/zram0/mem_limit
6) Activate
7) Activate
===========
::
@ -155,7 +186,7 @@ Examples::
mkfs.ext4 /dev/zram1
mount /dev/zram1 /tmp
7) Add/remove zram devices
8) Add/remove zram devices
==========================
zram provides a control interface, which enables dynamic (on-demand) device
@ -175,7 +206,7 @@ execute::
echo X > /sys/class/zram-control/hot_remove
8) Stats
9) Stats
========
Per-device statistics are exported as various nodes under /sys/block/zram<id>/
@ -277,15 +308,15 @@ a single line of text and contains the following stats separated by whitespace:
Unit: 4K bytes
============== =============================================================
9) Deactivate
=============
10) Deactivate
==============
::
swapoff /dev/zram0
umount /dev/zram1
10) Reset
11) Reset
=========
Write any positive value to 'reset' sysfs node::