xfs: improve handling of busy extents in the low-level allocator

Currently we force the log and simply try again if we hit a busy extent,
but especially with online discard enabled it might take a while after
the log force for the busy extents to disappear, and we might have
already completed our second pass.

So instead we add a new waitqueue and a generation counter to the pag
structure so that we can do wakeups once we've removed busy extents,
and we replace the single retry with an unconditional one - after
all we hold the AGF buffer lock, so no other allocations or frees
can be racing with us in this AG.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/fs/xfs/xfs_extent_busy.h b/fs/xfs/xfs_extent_busy.h
index bfff284..60195ea 100644
--- a/fs/xfs/xfs_extent_busy.h
+++ b/fs/xfs/xfs_extent_busy.h
@@ -58,9 +58,16 @@ void
 xfs_extent_busy_reuse(struct xfs_mount *mp, xfs_agnumber_t agno,
 	xfs_agblock_t fbno, xfs_extlen_t flen, bool userdata);
 
+bool
+xfs_extent_busy_trim(struct xfs_alloc_arg *args, xfs_agblock_t *bno,
+		xfs_extlen_t *len, unsigned *busy_gen);
+
+void
+xfs_extent_busy_flush(struct xfs_mount *mp, struct xfs_perag *pag,
+	unsigned busy_gen);
+
 void
-xfs_extent_busy_trim(struct xfs_alloc_arg *args, xfs_agblock_t bno,
-	xfs_extlen_t len, xfs_agblock_t *rbno, xfs_extlen_t *rlen);
+xfs_extent_busy_wait_all(struct xfs_mount *mp);
 
 int
 xfs_extent_busy_ag_cmp(void *priv, struct list_head *a, struct list_head *b);