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docs: filesystems: document the squashfs specific mount options 

When SQUASHFS_CHOICE_DECOMP_BY_MOUNT is set, the "threads" mount option
can be used to specify the decompression mode: single-threaded,
multi-threaded, percpu or the number of threads used for decompression. 
When SQUASHFS_CHOICE_DECOMP_BY_MOUNT is not set, SQUASHFS_DECOMP_MULTI and
SQUASHFS_MOUNT_DECOMP_THREADS are both set, the "threads" option can also
be used to specify the number of threads used for decompression.  This
mount option is only mentioned in fs/squashfs/Kconfig, which makes it
difficult to find.

Another mount option available is "errors", which can be configured to
panic the kernel when squashfs errors are encountered.

Add both these options to the squashfs documentation, making them more
noticeable.

Link: https://lkml.kernel.org/r/20231117161215.140282-1-amiculas@cisco.com
Signed-off-by: Ariel Miculas <amiculas@cisco.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Phillip Lougher <phillip@squashfs.org.uk>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Ariel Miculas 2023-11-17 18:12:14 +02:00 committed by Andrew Morton
parent 71aa3419e9
commit 48aa137e5a
1 changed files with 60 additions and 0 deletions
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60
Documentation/filesystems/squashfs.rst
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@ -64,6 +64,66 @@ obtained from this site also.
The squashfs-tools development tree is now located on kernel.org
git://git.kernel.org/pub/scm/fs/squashfs/squashfs-tools.git
2.1 Mount options
-----------------
=================== =========================================================
errors=%s Specify whether squashfs errors trigger a kernel panic
or not
========== =============================================
continue errors don't trigger a panic (default)
panic trigger a panic when errors are encountered,
similar to several other filesystems (e.g.
btrfs, ext4, f2fs, GFS2, jfs, ntfs, ubifs)
This allows a kernel dump to be saved,
useful for analyzing and debugging the
corruption.
========== =============================================
threads=%s Select the decompression mode or the number of threads
If SQUASHFS_CHOICE_DECOMP_BY_MOUNT is set:
========== =============================================
single use single-threaded decompression (default)
Only one block (data or metadata) can be
decompressed at any one time. This limits
CPU and memory usage to a minimum, but it
also gives poor performance on parallel I/O
workloads when using multiple CPU machines
due to waiting on decompressor availability.
multi use up to two parallel decompressors per core
If you have a parallel I/O workload and your
system has enough memory, using this option
may improve overall I/O performance. It
dynamically allocates decompressors on a
demand basis.
percpu use a maximum of one decompressor per core
It uses percpu variables to ensure
decompression is load-balanced across the
cores.
1|2|3|... configure the number of threads used for
decompression
The upper limit is num_online_cpus() * 2.
========== =============================================
If SQUASHFS_CHOICE_DECOMP_BY_MOUNT is **not** set and
SQUASHFS_DECOMP_MULTI, SQUASHFS_MOUNT_DECOMP_THREADS are
both set:
========== =============================================
2|3|... configure the number of threads used for
decompression
The upper limit is num_online_cpus() * 2.
========== =============================================
=================== =========================================================
3. Squashfs Filesystem Design
-----------------------------