+ documentation-zram-correct-algo-parameters-configuration-documentation.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: Documentation: zram: correct algo parameters configuration documentation
has been added to the -mm mm-unstable branch.  Its filename is
     documentation-zram-correct-algo-parameters-configuration-documentation.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/documentation-zram-correct-algo-parameters-configuration-documentation.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@chromium.org>
Subject: Documentation: zram: correct algo parameters configuration documentation
Date: Thu, 30 Jul 2026 16:51:46 +0900

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>
---

 Documentation/admin-guide/blockdev/zram.rst |   34 +++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

--- a/Documentation/admin-guide/blockdev/zram.rst~documentation-zram-correct-algo-parameters-configuration-documentation
+++ a/Documentation/admin-guide/blockdev/zram.rst
@@ -109,14 +109,41 @@ path to the `dict` along with other para
 	#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 ca
 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
 ============
 
_

Patches currently in -mm which might be from senozhatsky@chromium.org are

documentation-zram-remove-sections-numbering.patch
zram-set-default-primary-compressor-in-zram_destroy_comps.patch
zram-validate-deflate-params.patch
documentation-zram-correct-algo-parameters-configuration-documentation.patch