xfs: don't cache inodes read through bulkstat

When we read inodes via bulkstat, we generally only read them once
and then throw them away - they never get used again. If we retain
them in cache, then it simply causes the working set of inodes and
other cached items to be reclaimed just so the inode cache can grow.

Avoid this problem by marking inodes read by bulkstat not to be
cached and check this flag in .drop_inode to determine whether the
inode should be added to the VFS LRU or not. If the inode lookup
hits an already cached inode, then don't set the flag. If the inode
lookup hits an inode marked with no cache flag, remove the flag and
allow it to be cached once the current reference goes away.

Inodes marked as not cached will get cleaned up by the background
inode reclaim or via memory pressure, so they will still generate
some short term cache pressure. They will, however, be reclaimed
much sooner and in preference to cache hot inodes.

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

4 files changed, 28 insertions, 4 deletions

diff --git a/fs/xfs/xfs_iget.c b/fs/xfs/xfs_iget.c
index a98cb4524e6c..bcc6c249b2c7 100644
--- a/fs/xfs/xfs_iget.c
+++ b/fs/xfs/xfs_iget.c
@@ -289,7 +289,7 @@ xfs_iget_cache_hit(
         if (lock_flags != 0)
                 xfs_ilock(ip, lock_flags);
 
-        xfs_iflags_clear(ip, XFS_ISTALE);
+        xfs_iflags_clear(ip, XFS_ISTALE | XFS_IDONTCACHE);
         XFS_STATS_INC(xs_ig_found);
 
         return 0;
@@ -314,6 +314,7 @@ xfs_iget_cache_miss(
         struct xfs_inode        *ip;
         int                     error;
         xfs_agino_t             agino = XFS_INO_TO_AGINO(mp, ino);
+        int                     iflags;
 
         ip = xfs_inode_alloc(mp, ino);
         if (!ip)
@@ -358,8 +359,11 @@ xfs_iget_cache_miss(
          * memory barrier that ensures this detection works correctly at lookup
          * time.
          */
+        iflags = XFS_INEW;
+        if (flags & XFS_IGET_DONTCACHE)
+                iflags |= XFS_IDONTCACHE;
         ip->i_udquot = ip->i_gdquot = NULL;
-        xfs_iflags_set(ip, XFS_INEW);
+        xfs_iflags_set(ip, iflags);
 
         /* insert the new inode */
         spin_lock(&pag->pag_ici_lock);
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index f123dbe6d42a..7fee3387e1c8 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -387,10 +387,11 @@ xfs_set_projid(struct xfs_inode *ip,
 #define XFS_IFLOCK              (1 << __XFS_IFLOCK_BIT)
 #define __XFS_IPINNED_BIT       8        /* wakeup key for zero pin count */
 #define XFS_IPINNED             (1 << __XFS_IPINNED_BIT)
+#define XFS_IDONTCACHE          (1 << 9) /* don't cache the inode long term */
 
 /*
  * Per-lifetime flags need to be reset when re-using a reclaimable inode during
- * inode lookup. Thi prevents unintended behaviour on the new inode from
+ * inode lookup. This prevents unintended behaviour on the new inode from
  * ocurring.
  */
 #define XFS_IRECLAIM_RESET_FLAGS        \
@@ -553,6 +554,7 @@ do { \
  */
 #define XFS_IGET_CREATE         0x1
 #define XFS_IGET_UNTRUSTED      0x2
+#define XFS_IGET_DONTCACHE      0x4
 
 int             xfs_inotobp(struct xfs_mount *, struct xfs_trans *,
                             xfs_ino_t, struct xfs_dinode **,
diff --git a/fs/xfs/xfs_itable.c b/fs/xfs/xfs_itable.c
index 9720c54bbed0..acc2bf264dab 100644
--- a/fs/xfs/xfs_itable.c
+++ b/fs/xfs/xfs_itable.c
@@ -75,7 +75,8 @@ xfs_bulkstat_one_int(
                 return XFS_ERROR(ENOMEM);
 
         error = xfs_iget(mp, NULL, ino,
-                         XFS_IGET_UNTRUSTED, XFS_ILOCK_SHARED, &ip);
+                         (XFS_IGET_DONTCACHE | XFS_IGET_UNTRUSTED),
+                         XFS_ILOCK_SHARED, &ip);
         if (error) {
                 *stat = BULKSTAT_RV_NOTHING;
                 goto out_free;
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 5484888d39c4..e1c623b43ab2 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -950,6 +950,22 @@ xfs_fs_evict_inode(
         xfs_inactive(ip);
 }
 
+/*
+ * We do an unlocked check for XFS_IDONTCACHE here because we are already
+ * serialised against cache hits here via the inode->i_lock and igrab() in
+ * xfs_iget_cache_hit(). Hence a lookup that might clear this flag will not be
+ * racing with us, and it avoids needing to grab a spinlock here for every inode
+ * we drop the final reference on.
+ */
+STATIC int
+xfs_fs_drop_inode(
+        struct inode            *inode)
+{
+        struct xfs_inode        *ip = XFS_I(inode);
+
+        return generic_drop_inode(inode) || (ip->i_flags & XFS_IDONTCACHE);
+}
+
 STATIC void
 xfs_free_fsname(
         struct xfs_mount        *mp)
@@ -1434,6 +1450,7 @@ static const struct super_operations xfs_super_operations = {
         .destroy_inode          = xfs_fs_destroy_inode,
         .dirty_inode            = xfs_fs_dirty_inode,
         .evict_inode            = xfs_fs_evict_inode,
+        .drop_inode             = xfs_fs_drop_inode,
         .put_super              = xfs_fs_put_super,
         .sync_fs                = xfs_fs_sync_fs,
         .freeze_fs              = xfs_fs_freeze,