xfs: add a shrinker to background inode reclaim

On low memory boxes or those with highmem, kernel can OOM before the
background reclaims inodes via xfssyncd. Add a shrinker to run inode
reclaim so that it inode reclaim is expedited when memory is low.

This is more complex than it needs to be because the VM folk don't
want a context added to the shrinker infrastructure. Hence we need
to add a global list of XFS mount structures so the shrinker can
traverse them.

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

1 files changed, 105 insertions, 7 deletions

diff --git a/fs/xfs/linux-2.6/xfs_sync.c b/fs/xfs/linux-2.6/xfs_sync.c
index fd9698215759..a427c638d909 100644
--- a/fs/xfs/linux-2.6/xfs_sync.c
+++ b/fs/xfs/linux-2.6/xfs_sync.c
@@ -95,7 +95,8 @@ xfs_inode_ag_walk(
                                            struct xfs_perag *pag, int flags),
         int                     flags,
         int                     tag,
-        int                     exclusive)
+        int                     exclusive,
+        int                     *nr_to_scan)
 {
         uint32_t                first_index;
         int                     last_error = 0;
@@ -134,7 +135,7 @@ restart:
                 if (error == EFSCORRUPTED)
                         break;
 
-        } while (1);
+        } while ((*nr_to_scan)--);
 
         if (skipped) {
                 delay(1);
@@ -150,12 +151,15 @@ xfs_inode_ag_iterator(
                                            struct xfs_perag *pag, int flags),
         int                     flags,
         int                     tag,
-        int                     exclusive)
+        int                     exclusive,
+        int                     *nr_to_scan)
 {
         int                     error = 0;
         int                     last_error = 0;
         xfs_agnumber_t          ag;
+        int                     nr;
 
+        nr = nr_to_scan ? *nr_to_scan : INT_MAX;
         for (ag = 0; ag < mp->m_sb.sb_agcount; ag++) {
                 struct xfs_perag        *pag;
 
@@ -165,14 +169,18 @@ xfs_inode_ag_iterator(
                         continue;
                 }
                 error = xfs_inode_ag_walk(mp, pag, execute, flags, tag,
-                                                exclusive);
+                                                exclusive, &nr);
                 xfs_perag_put(pag);
                 if (error) {
                         last_error = error;
                         if (error == EFSCORRUPTED)
                                 break;
                 }
+                if (nr <= 0)
+                        break;
         }
+        if (nr_to_scan)
+                *nr_to_scan = nr;
         return XFS_ERROR(last_error);
 }
 
@@ -291,7 +299,7 @@ xfs_sync_data(
         ASSERT((flags & ~(SYNC_TRYLOCK|SYNC_WAIT)) == 0);
 
         error = xfs_inode_ag_iterator(mp, xfs_sync_inode_data, flags,
-                                      XFS_ICI_NO_TAG, 0);
+                                      XFS_ICI_NO_TAG, 0, NULL);
         if (error)
                 return XFS_ERROR(error);
 
@@ -310,7 +318,7 @@ xfs_sync_attr(
         ASSERT((flags & ~SYNC_WAIT) == 0);
 
         return xfs_inode_ag_iterator(mp, xfs_sync_inode_attr, flags,
-                                     XFS_ICI_NO_TAG, 0);
+                                     XFS_ICI_NO_TAG, 0, NULL);
 }
 
 STATIC int
@@ -673,6 +681,7 @@ __xfs_inode_set_reclaim_tag(
         radix_tree_tag_set(&pag->pag_ici_root,
                            XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino),
                            XFS_ICI_RECLAIM_TAG);
+        pag->pag_ici_reclaimable++;
 }
 
 /*
@@ -705,6 +714,7 @@ __xfs_inode_clear_reclaim_tag(
 {
         radix_tree_tag_clear(&pag->pag_ici_root,
                         XFS_INO_TO_AGINO(mp, ip->i_ino), XFS_ICI_RECLAIM_TAG);
+        pag->pag_ici_reclaimable--;
 }
 
 /*
@@ -854,5 +864,93 @@ xfs_reclaim_inodes(
         int             mode)
 {
         return xfs_inode_ag_iterator(mp, xfs_reclaim_inode, mode,
-                                        XFS_ICI_RECLAIM_TAG, 1);
+                                        XFS_ICI_RECLAIM_TAG, 1, NULL);
+}
+
+/*
+ * 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(
+        int             nr_to_scan,
+        gfp_t           gfp_mask)
+{
+        struct xfs_mount *mp;
+        struct xfs_perag *pag;
+        xfs_agnumber_t  ag;
+        int             reclaimable = 0;
+
+        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_ICI_RECLAIM_TAG, 1, &nr_to_scan);
+                        if (nr_to_scan <= 0)
+                                break;
+                }
+                up_read(&xfs_mount_list_lock);
+        }
+
+        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);
+                        if (!pag->pag_ici_init) {
+                                xfs_perag_put(pag);
+                                continue;
+                        }
+                        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);
+}
+
+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);
 }