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>

1 files changed, 42 insertions, 60 deletions

diff --git a/fs/xfs/xfs_sync.c b/fs/xfs/xfs_sync.c
index 85d03e6a2677..7b2bccc4d67b 100644
--- 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))
@@ -728,6 +719,13 @@ restart:
                 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.
          *
          * We do a nonblocking flush here even if we are doing a SYNC_WAIT
@@ -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;
 }
 
 /*