[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>

2 files changed, 13 insertions, 17 deletions

diff --git a/fs/xfs/xfs_iget.c b/fs/xfs/xfs_iget.c
index bb33113eef9f..b53854325266 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;
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 39ef9c36ea55..3b544db1790b 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -189,6 +189,7 @@ typedef struct xfs_ihash {
  */
 typedef struct xfs_chashlist {
         struct xfs_chashlist    *chl_next;
+        struct xfs_chashlist    *chl_prev;
         struct xfs_inode        *chl_ip;
         xfs_daddr_t             chl_blkno;      /* starting block number of
                                                  * the cluster */