[XFS] Fix inode reclaim scalability regression. When a filesystem has

millions of inodes cached and has sparse cluster population, removing
inodes from the cluster hash consumes excessive amounts of CPU time.
Reduce the CPU cost by making removal O(1) via use of a double linked list
for the hash chains.

SGI-PV: 951551
SGI-Modid: xfs-linux-melb:xfs-kern:25683a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>

1 files changed, 12 insertions, 17 deletions

diff --git a/fs/xfs/xfs_iget.c b/fs/xfs/xfs_iget.c
index bb33113..b538543 100644
--- a/fs/xfs/xfs_iget.c
+++ b/fs/xfs/xfs_iget.c
@@ -421,7 +421,10 @@ finish_inode:
 			ip->i_chash = chlnew;
 			chlnew->chl_ip = ip;
 			chlnew->chl_blkno = ip->i_blkno;
+			if (ch->ch_list)
+				ch->ch_list->chl_prev = chlnew;
 			chlnew->chl_next = ch->ch_list;
+			chlnew->chl_prev = NULL;
 			ch->ch_list = chlnew;
 			chlnew = NULL;
 		}
@@ -723,23 +726,15 @@ xfs_iextract(
 		ASSERT(ip->i_cnext == ip && ip->i_cprev == ip);
 		ASSERT(ip->i_chash != NULL);
 		chm=NULL;
-		for (chl = ch->ch_list; chl != NULL; chl = chl->chl_next) {
-			if (chl->chl_blkno == ip->i_blkno) {
-				if (chm == NULL) {
-					/* first item on the list */
-					ch->ch_list = chl->chl_next;
-				} else {
-					chm->chl_next = chl->chl_next;
-				}
-				kmem_zone_free(xfs_chashlist_zone, chl);
-				break;
-			} else {
-				ASSERT(chl->chl_ip != ip);
-				chm = chl;
-			}
-		}
-		ASSERT_ALWAYS(chl != NULL);
-       } else {
+		chl = ip->i_chash;
+		if (chl->chl_prev)
+			chl->chl_prev->chl_next = chl->chl_next;
+		else
+			ch->ch_list = chl->chl_next;
+		if (chl->chl_next)
+			chl->chl_next->chl_prev = chl->chl_prev;
+		kmem_zone_free(xfs_chashlist_zone, chl);
+	} else {
 		/* delete one inode from a non-empty list */
 		iq = ip->i_cnext;
 		iq->i_cprev = ip->i_cprev;