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Message-ID: <20240712051850.484318-24-senozhatsky@chromium.org> Date: Fri, 12 Jul 2024 14:18:34 +0900 From: Sergey Senozhatsky <senozhatsky@...omium.org> To: Andrew Morton <akpm@...ux-foundation.org>, Minchan Kim <minchan@...nel.org> Cc: linux-kernel@...r.kernel.org, Sergey Senozhatsky <senozhatsky@...omium.org> Subject: [PATCH v6 23/23] Documentation/zram: add documentation for algorithm parameters Document brief description of compression algorithms' parameters: compression level and pre-trained dictionary. Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org> --- Documentation/admin-guide/blockdev/zram.rst | 45 ++++++++++++++++----- 1 file changed, 36 insertions(+), 9 deletions(-) diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst index 091e8bb38887..e3cdbf4ba61f 100644 --- a/Documentation/admin-guide/blockdev/zram.rst +++ b/Documentation/admin-guide/blockdev/zram.rst @@ -102,15 +102,33 @@ Examples:: #select lzo compression algorithm echo lzo > /sys/block/zram0/comp_algorithm -For the time being, the `comp_algorithm` content does not necessarily -show every compression algorithm supported by the kernel. We keep this -list primarily to simplify device configuration and one can configure -a new device with a compression algorithm that is not listed in -`comp_algorithm`. The thing is that, internally, ZRAM uses Crypto API -and, if some of the algorithms were built as modules, it's impossible -to list all of them using, for instance, /proc/crypto or any other -method. This, however, has an advantage of permitting the usage of -custom crypto compression modules (implementing S/W or H/W compression). +For the time being, the `comp_algorithm` content shows only compression +algorithms that are supported by zram. + +It is also possible to pass algorithm specific configuration parameters:: + + #set compression level to 8 + echo "zstd level=8" > /sys/block/zram0/comp_algorithm + +Note that `comp_algorithm` also supports `algo=name` format:: + + #set compression level to 8 + echo "algo=zstd level=8" > /sys/block/zram0/comp_algorithm + +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 dictionary along with other parameters:: + + #pass path to pre-trained dictionary + echo "algo=zstd dict=/etc/dictioary" > /sys/block/zram0/comp_algorithm + +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). 4) Set Disksize =============== @@ -442,6 +460,15 @@ configuration::: #select deflate recompression algorithm, priority 2 echo "algo=deflate priority=2" > /sys/block/zramX/recomp_algorithm +The `recomp_algorithm` also supports algorithm configuration parameters, e.g. +compression level and pre-trained dircionary:: + + #pass compression level + echo "algo=zstd level=8" > /sys/block/zramX/recomp_algorithm + + #pass path to pre-trained dictionary + echo "algo=zstd dict=/etc/dictioary" > /sys/block/zramX/recomp_algorithm + Another device attribute that CONFIG_ZRAM_MULTI_COMP enables is recompress, which controls recompression. -- 2.45.2.993.g49e7a77208-goog
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