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btrfs-progs: docs: fix formatting of btrfs(5) 

Two paragraphs for 'discard' mount option were not aligned in the
section and the swapfile bullet list was squashed to one line. All in
the manual page output.

Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
David Sterba 2019-08-06 15:52:35 +02:00
parent fcebb87f52
commit b4cadc2ac9
1 changed files with 8 additions and 7 deletions
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15
Documentation/btrfs-man5.asciidoc
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@ -217,14 +217,14 @@ support discard for it to work. if the backing device does not support
asynchronous queued TRIM, then this operation can severely degrade performance, asynchronous queued TRIM, then this operation can severely degrade performance,
because a synchronous TRIM operation will be attempted instead. Queued TRIM because a synchronous TRIM operation will be attempted instead. Queued TRIM
requires newer than SATA revision 3.1 chipsets and devices. requires newer than SATA revision 3.1 chipsets and devices.
+
If it is not necessary to immediately discard freed blocks, then the `fstrim` If it is not necessary to immediately discard freed blocks, then the `fstrim`
tool can be used to discard all free blocks in a batch. Scheduling a TRIM tool can be used to discard all free blocks in a batch. Scheduling a TRIM
during a period of low system activity will prevent latent interference with during a period of low system activity will prevent latent interference with
the performance of other operations. Also, a device may ignore the TRIM command the performance of other operations. Also, a device may ignore the TRIM command
if the range is too small, so running a batch discard has a greater probability if the range is too small, so running a batch discard has a greater probability
of actually discarding the blocks. of actually discarding the blocks.
+
If discarding is not necessary to be done at the block freeing time, there's If discarding is not necessary to be done at the block freeing time, there's
`fstrim`(8) tool that lets the filesystem discard all free blocks in a batch, `fstrim`(8) tool that lets the filesystem discard all free blocks in a batch,
possibly not much interfering with other operations. Also, the device may possibly not much interfering with other operations. Also, the device may
@ -639,31 +639,32 @@ SWAPFILE SUPPORT
The swapfile is supported since kernel 5.0. Use `swapon`(8) to activate the The swapfile is supported since kernel 5.0. Use `swapon`(8) to activate the
swapfile. There are some limitations of the implementation in btrfs and linux swapfile. There are some limitations of the implementation in btrfs and linux
swap subystem: swap subystem:
+
* filesystem - must be only single device * filesystem - must be only single device
* swapfile - the containing subvolume cannot be snapshotted * swapfile - the containing subvolume cannot be snapshotted
* swapfile - must be preallocated * swapfile - must be preallocated
* swapfile - must be nodatacow (ie. also nodatasum) * swapfile - must be nodatacow (ie. also nodatasum)
* swapfile - must not be compressed * swapfile - must not be compressed
+
The limitations come namely from the COW-based design and mapping layer of The limitations come namely from the COW-based design and mapping layer of
blocks that allows the advanced features like relocation and multi-device blocks that allows the advanced features like relocation and multi-device
filesystems. However, the swap subsystem expects simpler mapping and no filesystems. However, the swap subsystem expects simpler mapping and no
background changes of the file blocks once they've been attached to swap. background changes of the file blocks once they've been attached to swap.
+
With active swapfiles, the following whole-filesystem operations will skip With active swapfiles, the following whole-filesystem operations will skip
swapfile extents or may fail: swapfile extents or may fail:
* balance - block groups with swapfile extents are skipped and reported, the rest will be processed normally * balance - block groups with swapfile extents are skipped and reported, the rest will be processed normally
* resize grow - unaffected * resize grow - unaffected
* resize shrink - works as long as the extents are outside of the shrunk range * resize shrink - works as long as the extents are outside of the shrunk range
* device add - a new device does not interfere with existing swapfile and this operation will work, though no new swapfile can be activated afterwards * device add - a new device does not interfere with existing swapfile and this operation will work, though no new swapfile can be activated afterwards
* device delete - if the device has been added as above, it can be also deleted * device delete - if the device has been added as above, it can be also deleted
* device replace - dtto * device replace - dtto
+
When there are no active swapfiles and a whole-filesystem exclusive operation When there are no active swapfiles and a whole-filesystem exclusive operation
is running (ie. balance, device delete, shrink), the swapfiles cannot be is running (ie. balance, device delete, shrink), the swapfiles cannot be
temporarily activated. The operation must finish first. temporarily activated. The operation must finish first.
+
-------------------- --------------------
# truncate -s 0 swapfile # truncate -s 0 swapfile
# chattr +C swapfile # chattr +C swapfile