superblock: add filesystem shrinker operations

Now we have a per-superblock shrinker implementation, we can add a
filesystem specific callout to it to allow filesystem internal
caches to be shrunk by the superblock shrinker.

Rather than perpetuate the multipurpose shrinker callback API (i.e.
nr_to_scan == 0 meaning "tell me how many objects freeable in the
cache), two operations will be added. The first will return the
number of objects that are freeable, the second is the actual
shrinker call.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 33 insertions, 12 deletions

diff --git a/fs/super.c b/fs/super.c
index 37a75410079e..5101f0544960 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -48,7 +48,8 @@ DEFINE_SPINLOCK(sb_lock);
 static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
 {
         struct super_block *sb;
-        int count;
+        int     fs_objects = 0;
+        int     total_objects;
 
         sb = container_of(shrink, struct super_block, s_shrink);
 
@@ -62,22 +63,42 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
         if (!grab_super_passive(sb))
                 return -1;
 
-        if (sc->nr_to_scan) {
-                /* proportion the scan between the two caches */
-                int total;
+        if (sb->s_op && sb->s_op->nr_cached_objects)
+                fs_objects = sb->s_op->nr_cached_objects(sb);
+
+        total_objects = sb->s_nr_dentry_unused +
+                        sb->s_nr_inodes_unused + fs_objects + 1;
 
-                total = sb->s_nr_dentry_unused + sb->s_nr_inodes_unused + 1;
-                count = (sc->nr_to_scan * sb->s_nr_dentry_unused) / total;
+        if (sc->nr_to_scan) {
+                int     dentries;
+                int     inodes;
+
+                /* proportion the scan between the caches */
+                dentries = (sc->nr_to_scan * sb->s_nr_dentry_unused) /
+                                                        total_objects;
+                inodes = (sc->nr_to_scan * sb->s_nr_inodes_unused) /
+                                                        total_objects;
+                if (fs_objects)
+                        fs_objects = (sc->nr_to_scan * fs_objects) /
+                                                        total_objects;
+                /*
+                 * prune the dcache first as the icache is pinned by it, then
+                 * prune the icache, followed by the filesystem specific caches
+                 */
+                prune_dcache_sb(sb, dentries);
+                prune_icache_sb(sb, inodes);
 
-                /* prune dcache first as icache is pinned by it */
-                prune_dcache_sb(sb, count);
-                prune_icache_sb(sb, sc->nr_to_scan - count);
+                if (fs_objects && sb->s_op->free_cached_objects) {
+                        sb->s_op->free_cached_objects(sb, fs_objects);
+                        fs_objects = sb->s_op->nr_cached_objects(sb);
+                }
+                total_objects = sb->s_nr_dentry_unused +
+                                sb->s_nr_inodes_unused + fs_objects;
         }
 
-        count = ((sb->s_nr_dentry_unused + sb->s_nr_inodes_unused) / 100)
-                                                * sysctl_vfs_cache_pressure;
+        total_objects = (total_objects / 100) * sysctl_vfs_cache_pressure;
         drop_super(sb);
-        return count;
+        return total_objects;
 }
 
 /**