xfs: add online discard support

Now that we have reliably tracking of deleted extents in a
transaction we can easily implement "online" discard support
which calls blkdev_issue_discard once a transaction commits.

The actual discard is a two stage operation as we first have
to mark the busy extent as not available for reuse before we
can start the actual discard.  Note that we don't bother
supporting discard for the non-delaylog mode.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/Documentation/filesystems/xfs.txt b/Documentation/filesystems/xfs.txt
index 7bff3e4f35df..3fc0c31a6f5d 100644
--- a/Documentation/filesystems/xfs.txt
+++ b/Documentation/filesystems/xfs.txt
@@ -39,6 +39,12 @@ When mounting an XFS filesystem, the following options are accepted.
         drive level write caching to be enabled, for devices that
         support write barriers.
 
+  discard
+        Issue command to let the block device reclaim space freed by the
+        filesystem.  This is useful for SSD devices, thinly provisioned
+        LUNs and virtual machine images, but may have a performance
+        impact.  This option is incompatible with the nodelaylog option.
+
   dmapi
         Enable the DMAPI (Data Management API) event callouts.
         Use with the "mtpt" option.