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| author | Sergey Senozhatsky <senozhatsky@chromium.org> | 2026-07-30 16:51:46 +0900 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-08-24 18:42:57 -0700 |
| commit | f74e6dff5440f662bced614b723a7d8f2b05919d (patch) | |
| tree | ceefd089947619585cc775d7428b78e992237298 /Documentation/admin-guide/blockdev | |
| parent | 9477820c63cbf4d97114238f3d1ff10dfd6bee3f (diff) | |
| download | linux-f74e6dff5440f662bced614b723a7d8f2b05919d.tar.gz linux-f74e6dff5440f662bced614b723a7d8f2b05919d.zip | |
Documentation: zram: correct algo parameters configuration documentation
zram has always reset all previously set parameters for the given
algorithm in comp_params_store(). Make documentation more clear and
explicitly state that all relevant/necessary parameters should be set in
one configuration write.
Link: https://lore.kernel.org/20260730075158.1339787-1-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'Documentation/admin-guide/blockdev')
| -rw-r--r-- | Documentation/admin-guide/blockdev/zram.rst | 34 |
1 files changed, 33 insertions, 1 deletions
diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst index 2f6bbfd991fe..148b7cf3b924 100644 --- a/Documentation/admin-guide/blockdev/zram.rst +++ b/Documentation/admin-guide/blockdev/zram.rst @@ -109,14 +109,41 @@ path to the `dict` along with other parameters:: #pass path to pre-trained zstd dictionary echo "algo=zstd dict=/etc/dictionary" > /sys/block/zram0/algorithm_params + #pass path to pre-trained zstd dictionary and compression level + echo "algo=zstd level=8 dict=/etc/dictionary" > \ + /sys/block/zram0/algorithm_params + #same, but using algorithm priority + echo "algo=zstd priority=1" > /sys/block/zram0/recomp_algorithm echo "priority=1 dict=/etc/dictionary" > \ /sys/block/zram0/algorithm_params - #pass path to pre-trained zstd dictionary and compression level +Each write to `algorithm_params` replaces the entire set of parameters of +the corresponding algorithm, parameters that are not listed in the write +are reset to their default values. Configure all of the parameters of an +algorithm in one write:: + + #WRONG: the second write resets level back to its default value + echo "algo=zstd level=8" > /sys/block/zram0/algorithm_params + echo "algo=zstd dict=/etc/dictionary" > /sys/block/zram0/algorithm_params + + #RIGHT echo "algo=zstd level=8 dict=/etc/dictionary" > \ /sys/block/zram0/algorithm_params +Select the compression algorithm before configuring its parameters. The +parameters of one algorithm are not necessarily valid for another one, so +changing the algorithm of a particular priority resets that priority's +parameters:: + + #WRONG: comp_algorithm write resets the previously configured level + echo "level=8" > /sys/block/zram0/algorithm_params + echo zstd > /sys/block/zram0/comp_algorithm + + #RIGHT + echo zstd > /sys/block/zram0/comp_algorithm + echo "algo=zstd level=8" > /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 @@ -124,6 +151,11 @@ 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). +Parameters are handed over to the compression algorithm when the device is +initialised, hence invalid parameters (or parameters that the selected +algorithm does not support) are reported by the `disksize` write, and not +by the `algorithm_params` write that has configured them. + Set Disksize ============ |