The patch titled
Subject: Documentation/zram: add documentation for algorithm parameters
has been added to the -mm mm-unstable branch. Its filename is
documentation-zram-add-documentation-for-algorithm-parameters.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/documentation-zram-add-documentation-for-algorithm-parameters.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Subject: Documentation/zram: add documentation for algorithm parameters
Date: Mon, 2 Sep 2024 19:56:11 +0900
Document brief description of compression algorithms' parameters:
compression level and pre-trained dictionary.
Link: https://lkml.kernel.org/r/20240902105656.1383858-24-senozhatsky@xxxxxxxxxxxx
Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Nick Terrell <terrelln@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/blockdev/zram.rst | 45 +++++++++++++++---
1 file changed, 38 insertions(+), 7 deletions(-)
--- a/Documentation/admin-guide/blockdev/zram.rst~documentation-zram-add-documentation-for-algorithm-parameters
+++ a/Documentation/admin-guide/blockdev/zram.rst
@@ -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
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>/
@@ -277,7 +308,7 @@ a single line of text and contains the f
Unit: 4K bytes
============== =============================================================
-9) Deactivate
+10) Deactivate
=============
::
@@ -285,7 +316,7 @@ a single line of text and contains the f
swapoff /dev/zram0
umount /dev/zram1
-10) Reset
+11) Reset
=========
Write any positive value to 'reset' sysfs node::
_
Patches currently in -mm which might be from senozhatsky@xxxxxxxxxxxx are
lib-zstd-export-api-needed-for-dictionary-support.patch
lib-lz4hc-export-lz4_resetstreamhc-symbol.patch
lib-zstd-fix-null-deref-in-zstd_createcdict_advanced2.patch
zram-introduce-custom-comp-backends-api.patch
zram-add-lzo-and-lzorle-compression-backends-support.patch
zram-add-lz4-compression-backend-support.patch
zram-add-lz4hc-compression-backend-support.patch
zram-add-zstd-compression-backend-support.patch
zram-pass-estimated-src-size-hint-to-zstd.patch
zram-add-zlib-compression-backend-support.patch
zram-add-842-compression-backend-support.patch
zram-check-that-backends-array-has-at-least-one-backend.patch
zram-introduce-zcomp_params-structure.patch
zram-recalculate-zstd-compression-params-once.patch
zram-introduce-algorithm_params-device-attribute.patch
zram-add-support-for-dict-comp-config.patch
zram-introduce-zcomp_req-structure.patch
zram-introduce-zcomp_ctx-structure.patch
zram-move-immutable-comp-params-away-from-per-cpu-context.patch
zram-add-dictionary-support-to-lz4.patch
zram-add-dictionary-support-to-lz4hc.patch
zram-add-dictionary-support-to-zstd-backend.patch
documentation-zram-add-documentation-for-algorithm-parameters.patch
zram-support-priority-parameter-in-recompression.patch
