xfs: don't flush inodes from background inode reclaim

We already flush dirty inodes throug the AIL regularly, there is no reason
to have second thread compete with it and disturb the I/O pattern.  We still
do write inodes when doing a synchronous reclaim from the shrinker or during
unmount for now.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

diff --git a/fs/xfs/xfs_sync.c b/fs/xfs/xfs_sync.c
index 85d03e6a2677cbbe31450eaa909d4738686b3dad..7b2bccc4d67b94cce222769092c286a95003f005 100644 (file)
--- a/fs/xfs/xfs_sync.c
+++ b/fs/xfs/xfs_sync.c
@@ -631,11 +631,8 @@ xfs_reclaim_inode_grab(
 }
 
 /*
- * Inodes in different states need to be treated differently, and the return
- * value of xfs_iflush is not sufficient to get this right. The following table
- * lists the inode states and the reclaim actions necessary for non-blocking
- * reclaim:
- *
+ * Inodes in different states need to be treated differently. The following
+ * table lists the inode states and the reclaim actions necessary:
  *
  *     inode state          iflush ret         required action
  *      ---------------      ----------         ---------------
@@ -645,9 +642,8 @@ xfs_reclaim_inode_grab(
  *     stale, unpinned         0               reclaim
  *     clean, pinned(*)        0               requeue
  *     stale, pinned           EAGAIN          requeue
- *     dirty, delwri ok        0               requeue
- *     dirty, delwri blocked   EAGAIN          requeue
- *     dirty, sync flush       0               reclaim
+ *     dirty, async            -               requeue
+ *     dirty, sync             0               reclaim
  *
  * (*) dgc: I don't think the clean, pinned state is possible but it gets
  * handled anyway given the order of checks implemented.
@@ -658,26 +654,23 @@ xfs_reclaim_inode_grab(
  *
  * Also, because we get the flush lock first, we know that any inode that has
  * been flushed delwri has had the flush completed by the time we check that
- * the inode is clean. The clean inode check needs to be done before flushing
- * the inode delwri otherwise we would loop forever requeuing clean inodes as
- * we cannot tell apart a successful delwri flush and a clean inode from the
- * return value of xfs_iflush().
+ * the inode is clean.
  *
- * Note that because the inode is flushed delayed write by background
- * writeback, the flush lock may already be held here and waiting on it can
- * result in very long latencies. Hence for sync reclaims, where we wait on the
- * flush lock, the caller should push out delayed write inodes first before
- * trying to reclaim them to minimise the amount of time spent waiting. For
- * background relaim, we just requeue the inode for the next pass.
+ * Note that because the inode is flushed delayed write by AIL pushing, the
+ * flush lock may already be held here and waiting on it can result in very
+ * long latencies.  Hence for sync reclaims, where we wait on the flush lock,
+ * the caller should push the AIL first before trying to reclaim inodes to
+ * minimise the amount of time spent waiting.  For background relaim, we only
+ * bother to reclaim clean inodes anyway.
  *
  * Hence the order of actions after gaining the locks should be:
  *     bad             => reclaim
  *     shutdown        => unpin and reclaim
- *     pinned, delwri  => requeue
+ *     pinned, async   => requeue
  *     pinned, sync    => unpin
  *     stale           => reclaim
  *     clean           => reclaim
- *     dirty, delwri   => flush and requeue
+ *     dirty, async    => requeue
  *     dirty, sync     => flush, wait and reclaim
  */
 STATIC int
@@ -716,10 +709,8 @@ restart:
                goto reclaim;
        }
        if (xfs_ipincount(ip)) {
-               if (!(sync_mode & SYNC_WAIT)) {
-                       xfs_ifunlock(ip);
-                       goto out;
-               }
+               if (!(sync_mode & SYNC_WAIT))
+                       goto out_ifunlock;
                xfs_iunpin_wait(ip);
        }
        if (xfs_iflags_test(ip, XFS_ISTALE))
@@ -727,6 +718,13 @@ restart:
        if (xfs_inode_clean(ip))
                goto reclaim;
 
+       /*
+        * Never flush out dirty data during non-blocking reclaim, as it would
+        * just contend with AIL pushing trying to do the same job.
+        */
+       if (!(sync_mode & SYNC_WAIT))
+               goto out_ifunlock;
+
        /*
         * Now we have an inode that needs flushing.
         *
@@ -745,42 +743,13 @@ restart:
         * pass through will see the stale flag set on the inode.
         */
        error = xfs_iflush(ip, SYNC_TRYLOCK | sync_mode);
-       if (sync_mode & SYNC_WAIT) {
-               if (error == EAGAIN) {
-                       xfs_iunlock(ip, XFS_ILOCK_EXCL);
-                       /* backoff longer than in xfs_ifree_cluster */
-                       delay(2);
-                       goto restart;
-               }
-               xfs_iflock(ip);
-               goto reclaim;
-       }
-
-       /*
-        * When we have to flush an inode but don't have SYNC_WAIT set, we
-        * flush the inode out using a delwri buffer and wait for the next
-        * call into reclaim to find it in a clean state instead of waiting for
-        * it now. We also don't return errors here - if the error is transient
-        * then the next reclaim pass will flush the inode, and if the error
-        * is permanent then the next sync reclaim will reclaim the inode and
-        * pass on the error.
-        */
-       if (error && error != EAGAIN && !XFS_FORCED_SHUTDOWN(ip->i_mount)) {
-               xfs_warn(ip->i_mount,
-                       "inode 0x%llx background reclaim flush failed with %d",
-                       (long long)ip->i_ino, error);
+       if (error == EAGAIN) {
+               xfs_iunlock(ip, XFS_ILOCK_EXCL);
+               /* backoff longer than in xfs_ifree_cluster */
+               delay(2);
+               goto restart;
        }
-out:
-       xfs_iflags_clear(ip, XFS_IRECLAIM);
-       xfs_iunlock(ip, XFS_ILOCK_EXCL);
-       /*
-        * We could return EAGAIN here to make reclaim rescan the inode tree in
-        * a short while. However, this just burns CPU time scanning the tree
-        * waiting for IO to complete and xfssyncd never goes back to the idle
-        * state. Instead, return 0 to let the next scheduled background reclaim
-        * attempt to reclaim the inode again.
-        */
-       return 0;
+       xfs_iflock(ip);
 
 reclaim:
        xfs_ifunlock(ip);
@@ -814,8 +783,21 @@ reclaim:
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
 
        xfs_inode_free(ip);
-
        return error;
+
+out_ifunlock:
+       xfs_ifunlock(ip);
+out:
+       xfs_iflags_clear(ip, XFS_IRECLAIM);
+       xfs_iunlock(ip, XFS_ILOCK_EXCL);
+       /*
+        * We could return EAGAIN here to make reclaim rescan the inode tree in
+        * a short while. However, this just burns CPU time scanning the tree
+        * waiting for IO to complete and xfssyncd never goes back to the idle
+        * state. Instead, return 0 to let the next scheduled background reclaim
+        * attempt to reclaim the inode again.
+        */
+       return 0;
 }
 
 /*