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btrfs-progs: docs: add compression level support for mount options

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As of 5.1, btrfs now supports compression levels for zstd. Let users
know about this in the man page.

Pull-request: #204
Signed-off-by: Dennis Zhou <dennis@kernel.org>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Dennis Zhou 2019-09-19 03:11:15 -07:00 committed by David Sterba
parent 4b3e22e988
commit 483179bbae
1 changed files with 10 additions and 3 deletions
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13
Documentation/btrfs-man5.asciidoc
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@ -125,10 +125,10 @@ The upper bound is not forced, but a warning is printed if it's more than 300
seconds (5 minutes). Use with care. seconds (5 minutes). Use with care.
*compress*:: *compress*::
*compress='type'*:: *compress='type[:level]'*::
*compress-force*:: *compress-force*::
*compress-force='type'*:: *compress-force='type[:level]'*::
(default: off) (default: off, level support since: 5.1)
+ +
Control BTRFS file data compression. Type may be specified as 'zlib', Control BTRFS file data compression. Type may be specified as 'zlib',
'lzo', 'zstd' or 'no' (for no compression, used for remounting). If no type 'lzo', 'zstd' or 'no' (for no compression, used for remounting). If no type
@ -136,6 +136,13 @@ is specified, 'zlib' is used. If 'compress-force' is specified,
then compression will always be attempted, but the data may end up uncompressed then compression will always be attempted, but the data may end up uncompressed
if the compression would make them larger. if the compression would make them larger.
+ +
Both 'zlib' and 'zstd' (since version 5.1) expose the compression level as a
tunable knob with higher levels trading speed and memory ('zstd') for higher
compression ratios. This can be set by appending a colon and the desired level.
Zlib accepts the range [1, 9] and zstd accepts [1, 15]. If no level is set,
both currently use a default level of 3. The value 0 is an alias for the defaul
level.
+
Otherwise some simple heuristics are applied to detect an incompressible file. Otherwise some simple heuristics are applied to detect an incompressible file.
If the first blocks written to a file are not compressible, the whole file is If the first blocks written to a file are not compressible, the whole file is
permanently marked to skip compression. As this is too simple, the permanently marked to skip compression. As this is too simple, the