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btrfs-progs: docs: improve space cache documentation #571

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btrfs-progs: docs: improve space cache documentation #571

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12 changes: 2 additions & 10 deletions Documentation/btrfs-check.rst
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Expand Up @@ -79,17 +79,9 @@ SAFE OR ADVISORY OPTIONS
superblock is damaged.

--clear-space-cache v1|v2
completely wipe all free space cache of given type
completely remove the free space cache of the given version

For free space cache *v1*, the *clear_cache* kernel mount option only rebuilds
the free space cache for block groups that are modified while the filesystem is
mounted with that option. Thus, using this option with *v1* makes it possible
to actually clear the entire free space cache.

For free space cache *v2*, the *clear_cache* kernel mount option destroys
the entire free space cache. This option, with *v2* provides an alternative
method of clearing the free space cache that doesn't require mounting the
filesystem.
See also the *clear_cache* mount option.

--clear-ino-cache
remove leftover items pertaining to the deprecated inode map feature
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18 changes: 15 additions & 3 deletions Documentation/ch-mount-options.rst
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Expand Up @@ -89,8 +89,19 @@ check_int, check_int_data, check_int_print_mask=<value>
for more information.

clear_cache
Force clearing and rebuilding of the disk space cache if something
has gone wrong. See also: *space_cache*.
Force clearing and rebuilding of the free space cache if something
has gone wrong.

For free space cache *v1*, this only clears (and, unless *nospace_cache* is
used, rebuilds) the free space cache for block groups that are modified while
the filesystem is mounted with that option. To actually clear an entire free
space cache *v1*, see ``btrfs check --clear-space-cache v1``.

For free space cache *v2*, this clears the entire free space cache.
To do so without requiring to mounting the filesystem, see
``btrfs check --clear-space-cache v2``.

See also: *space_cache*.

commit=<seconds>
(since: 3.12, default: 30)
Expand Down Expand Up @@ -351,7 +362,8 @@ space_cache, space_cache=<version>, nospace_cache
implementation, which adds a new b-tree called the free space tree, addresses
this issue. Once enabled, the *v2* space cache will always be used and cannot
be disabled unless it is cleared. Use *clear_cache,space_cache=v1* or
*clear_cache,nospace_cache* to do so. If *v2* is enabled, kernels without *v2*
*clear_cache,nospace_cache* to do so. If *v2* is enabled, and *v1* space
cache will be cleared (at the first mount) and kernels without *v2*
support will only be able to mount the filesystem in read-only mode.

The :doc:`btrfs-check(8)<btrfs-check>` and `:doc:`mkfs.btrfs(8)<mkfs.btrfs>` commands have full *v2* free space
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