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>

6 files changed, 120 insertions, 9 deletions

diff --git a/fs/xfs/linux-2.6/xfs_super.c b/fs/xfs/linux-2.6/xfs_super.c
index 52e06b487ced..29f1edca76de 100644
--- a/fs/xfs/linux-2.6/xfs_super.c
+++ b/fs/xfs/linux-2.6/xfs_super.c
@@ -1209,6 +1209,7 @@ xfs_fs_put_super(
 
         xfs_unmountfs(mp);
         xfs_freesb(mp);
+        xfs_inode_shrinker_unregister(mp);
         xfs_icsb_destroy_counters(mp);
         xfs_close_devices(mp);
         xfs_dmops_put(mp);
@@ -1622,6 +1623,8 @@ xfs_fs_fill_super(
         if (error)
                 goto fail_vnrele;
 
+        xfs_inode_shrinker_register(mp);
+
         kfree(mtpt);
         return 0;
 
@@ -1867,6 +1870,7 @@ init_xfs_fs(void)
                 goto out_cleanup_procfs;
 
         vfs_initquota();
+        xfs_inode_shrinker_init();
 
         error = register_filesystem(&xfs_fs_type);
         if (error)
@@ -1894,6 +1898,7 @@ 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 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);
 }
diff --git a/fs/xfs/linux-2.6/xfs_sync.h b/fs/xfs/linux-2.6/xfs_sync.h
index d480c346cabb..cdcbaaca9880 100644
--- a/fs/xfs/linux-2.6/xfs_sync.h
+++ b/fs/xfs/linux-2.6/xfs_sync.h
@@ -53,6 +53,11 @@ void __xfs_inode_clear_reclaim_tag(struct xfs_mount *mp, struct xfs_perag *pag,
 int xfs_sync_inode_valid(struct xfs_inode *ip, struct xfs_perag *pag);
 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 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);
 
 #endif
diff --git a/fs/xfs/quota/xfs_qm_syscalls.c b/fs/xfs/quota/xfs_qm_syscalls.c
index 5d0ee8d492db..50bee07d6b0e 100644
--- a/fs/xfs/quota/xfs_qm_syscalls.c
+++ b/fs/xfs/quota/xfs_qm_syscalls.c
@@ -891,7 +891,8 @@ xfs_qm_dqrele_all_inodes(
         uint             flags)
 {
         ASSERT(mp->m_quotainfo);
-        xfs_inode_ag_iterator(mp, xfs_dqrele_inode, flags, XFS_ICI_NO_TAG, 0);
+        xfs_inode_ag_iterator(mp, xfs_dqrele_inode, flags,
+                                XFS_ICI_NO_TAG, 0, NULL);
 }
 
 /*------------------------------------------------------------------------*/
diff --git a/fs/xfs/xfs_ag.h b/fs/xfs/xfs_ag.h
index b1a5a1ff88ea..abb8222b88c9 100644
--- a/fs/xfs/xfs_ag.h
+++ b/fs/xfs/xfs_ag.h
@@ -223,6 +223,7 @@ typedef struct xfs_perag {
         int             pag_ici_init;   /* incore inode cache initialised */
         rwlock_t        pag_ici_lock;   /* incore inode lock */
         struct radix_tree_root pag_ici_root;    /* incore inode cache root */
+        int             pag_ici_reclaimable;    /* reclaimable inodes */
 #endif
         int             pagb_count;     /* pagb slots in use */
         xfs_perag_busy_t pagb_list[XFS_PAGB_NUM_SLOTS]; /* unstable blocks */
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 4fa0bc7b983e..9ff48a16a7ee 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -259,6 +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 */
 } xfs_mount_t;
 
 /*