GFS2: Support generation of discard requests

This patch allows GFS2 to generate discard requests for blocks which are
no longer useful to the filesystem (i.e. those which have been freed as
the result of an unlink operation). The requests are generated at the
time which those blocks become available for reuse in the filesystem.

In order to use this new feature, you have to specify the "discard"
mount option. The code coalesces adjacent blocks into a single extent
when generating the discard requests, thus generating the minimum
number.

If an error occurs when the request has been sent to the block device,
then it will print a message and turn off the requests for that
filesystem. If the problem is temporary, then you can use remount to
turn the option back on again. There is also a nodiscard mount option
so that you can use remount to turn discard requests off, if required.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 8fe0675120ac..3f29bd224ba1 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -416,7 +416,7 @@ struct gfs2_args {
         unsigned int ar_suiddir:1;              /* suiddir support */
         unsigned int ar_data:2;                 /* ordered/writeback */
         unsigned int ar_meta:1;                 /* mount metafs */
-        unsigned int ar_num_glockd;             /* Number of glockd threads */
+        unsigned int ar_discard:1;              /* discard requests */
 };
 
 struct gfs2_tune {