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>

4 files changed, 15 insertions, 53 deletions

diff --git a/fs/xfs/linux-2.6/xfs_super.c b/fs/xfs/linux-2.6/xfs_super.c
index f2d1718c916..80938c736c2 100644
--- a/fs/xfs/linux-2.6/xfs_super.c
+++ b/fs/xfs/linux-2.6/xfs_super.c
@@ -1883,7 +1883,6 @@ init_xfs_fs(void)
                 goto out_cleanup_procfs;
 
         vfs_initquota();
-        xfs_inode_shrinker_init();
 
         error = register_filesystem(&xfs_fs_type);
         if (error)
@@ -1911,7 +1910,6 @@ exit_xfs_fs(void)
 {
         vfs_exitquota();
         unregister_filesystem(&xfs_fs_type);
-        xfs_inode_shrinker_destroy();
         xfs_sysctl_unregister();
         xfs_cleanup_procfs();
         xfs_buf_terminate();
diff --git a/fs/xfs/linux-2.6/xfs_sync.c b/fs/xfs/linux-2.6/xfs_sync.c
index be375827af9..f433819611c 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);
 }
diff --git a/fs/xfs/linux-2.6/xfs_sync.h b/fs/xfs/linux-2.6/xfs_sync.h
index cdcbaaca988..e28139aaa4a 100644
--- a/fs/xfs/linux-2.6/xfs_sync.h
+++ b/fs/xfs/linux-2.6/xfs_sync.h
@@ -55,8 +55,6 @@ int xfs_inode_ag_iterator(struct xfs_mount *mp,
         int (*execute)(struct xfs_inode *ip, struct xfs_perag *pag, int flags),
         int flags, int tag, int write_lock, int *nr_to_scan);
 
-void xfs_inode_shrinker_init(void);
-void xfs_inode_shrinker_destroy(void);
 void xfs_inode_shrinker_register(struct xfs_mount *mp);
 void xfs_inode_shrinker_unregister(struct xfs_mount *mp);
 
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 1d2c7eed4ed..5761087ee8e 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -259,7 +259,7 @@ typedef struct xfs_mount {
         wait_queue_head_t       m_wait_single_sync_task;
         __int64_t               m_update_flags; /* sb flags we need to update
                                                    on the next remount,rw */
-        struct list_head        m_mplist;       /* inode shrinker mount list */
+        struct shrinker         m_inode_shrink; /* inode reclaim shrinker */
 } xfs_mount_t;
 
 /*