xfs: reduce the number of pagb_lock roundtrips in xfs_alloc_clear_busy

Instead of finding the per-ag and then taking and releasing the pagb_lock
for every single busy extent completed sort the list of busy extents and
only switch betweens AGs where nessecary.  This becomes especially important
with the online discard support which will hit this lock more often.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
index 9ca59be..7d56e88 100644
--- a/fs/xfs/xfs_log_cil.c
+++ b/fs/xfs/xfs_log_cil.c
@@ -361,13 +361,12 @@
 	int	abort)
 {
 	struct xfs_cil_ctx	*ctx = args;
-	struct xfs_busy_extent	*busyp, *n;
 
 	xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, ctx->lv_chain,
 					ctx->start_lsn, abort);
 
-	list_for_each_entry_safe(busyp, n, &ctx->busy_extents, list)
-		xfs_alloc_busy_clear(ctx->cil->xc_log->l_mp, busyp);
+	xfs_alloc_busy_sort(&ctx->busy_extents);
+	xfs_alloc_busy_clear(ctx->cil->xc_log->l_mp, &ctx->busy_extents);
 
 	spin_lock(&ctx->cil->xc_cil_lock);
 	list_del(&ctx->committing);