xfs: convert inode shrinker to per-filesystem contexts

Now the shrinker passes us a context, wire up a shrinker context per
filesystem. This allows us to remove the global mount list and the
locking problems that introduced. It also means that a shrinker call
does not need to traverse clean filesystems before finding a
filesystem with reclaimable inodes.  This significantly reduces
scanning overhead when lots of filesystems are present.

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

1 files changed, 14 insertions, 48 deletions

diff --git a/fs/xfs/linux-2.6/xfs_sync.c b/fs/xfs/linux-2.6/xfs_sync.c
index be375827af98..f433819611cb 100644
--- a/fs/xfs/linux-2.6/xfs_sync.c
+++ b/fs/xfs/linux-2.6/xfs_sync.c
@@ -828,14 +828,7 @@ xfs_reclaim_inodes(
 
 /*
  * Shrinker infrastructure.
- *
- * This is all far more complex than it needs to be. It adds a global list of
- * mounts because the shrinkers can only call a global context. We need to make
- * the shrinkers pass a context to avoid the need for global state.
  */
-static LIST_HEAD(xfs_mount_list);
-static struct rw_semaphore xfs_mount_list_lock;
-
 static int
 xfs_reclaim_inode_shrink(
         struct shrinker *shrink,
@@ -847,65 +840,38 @@ xfs_reclaim_inode_shrink(
         xfs_agnumber_t  ag;
         int             reclaimable = 0;
 
+        mp = container_of(shrink, struct xfs_mount, m_inode_shrink);
         if (nr_to_scan) {
                 if (!(gfp_mask & __GFP_FS))
                         return -1;
 
-                down_read(&xfs_mount_list_lock);
-                list_for_each_entry(mp, &xfs_mount_list, m_mplist) {
-                        xfs_inode_ag_iterator(mp, xfs_reclaim_inode, 0,
+                xfs_inode_ag_iterator(mp, xfs_reclaim_inode, 0,
                                         XFS_ICI_RECLAIM_TAG, 1, &nr_to_scan);
-                        if (nr_to_scan <= 0)
-                                break;
-                }
-                up_read(&xfs_mount_list_lock);
-        }
+                /* if we don't exhaust the scan, don't bother coming back */
+                if (nr_to_scan > 0)
+                        return -1;
+       }
 
-        down_read(&xfs_mount_list_lock);
-        list_for_each_entry(mp, &xfs_mount_list, m_mplist) {
-                for (ag = 0; ag < mp->m_sb.sb_agcount; ag++) {
-                        pag = xfs_perag_get(mp, ag);
-                        reclaimable += pag->pag_ici_reclaimable;
-                        xfs_perag_put(pag);
-                }
+        for (ag = 0; ag < mp->m_sb.sb_agcount; ag++) {
+                pag = xfs_perag_get(mp, ag);
+                reclaimable += pag->pag_ici_reclaimable;
+                xfs_perag_put(pag);
         }
-        up_read(&xfs_mount_list_lock);
         return reclaimable;
 }
 
-static struct shrinker xfs_inode_shrinker = {
-        .shrink = xfs_reclaim_inode_shrink,
-        .seeks = DEFAULT_SEEKS,
-};
-
-void __init
-xfs_inode_shrinker_init(void)
-{
-        init_rwsem(&xfs_mount_list_lock);
-        register_shrinker(&xfs_inode_shrinker);
-}
-
-void
-xfs_inode_shrinker_destroy(void)
-{
-        ASSERT(list_empty(&xfs_mount_list));
-        unregister_shrinker(&xfs_inode_shrinker);
-}
-
 void
 xfs_inode_shrinker_register(
         struct xfs_mount        *mp)
 {
-        down_write(&xfs_mount_list_lock);
-        list_add_tail(&mp->m_mplist, &xfs_mount_list);
-        up_write(&xfs_mount_list_lock);
+        mp->m_inode_shrink.shrink = xfs_reclaim_inode_shrink;
+        mp->m_inode_shrink.seeks = DEFAULT_SEEKS;
+        register_shrinker(&mp->m_inode_shrink);
 }
 
 void
 xfs_inode_shrinker_unregister(
         struct xfs_mount        *mp)
 {
-        down_write(&xfs_mount_list_lock);
-        list_del(&mp->m_mplist);
-        up_write(&xfs_mount_list_lock);
+        unregister_shrinker(&mp->m_inode_shrink);
 }