ext4: introduce aging to extent status tree

Introduce a simple aging to extent status tree. Each extent has a
REFERENCED bit which gets set when the extent is used. Shrinker then
skips entries with referenced bit set and clears the bit. Thus
frequently used extents have higher chances of staying in memory.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 17 insertions, 5 deletions

diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 3059649..e04d457 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -382,7 +382,7 @@ static void ext4_es_free_extent(struct inode *inode, struct extent_status *es)
 static int ext4_es_can_be_merged(struct extent_status *es1,
 				 struct extent_status *es2)
 {
-	if (ext4_es_status(es1) != ext4_es_status(es2))
+	if (ext4_es_type(es1) != ext4_es_type(es2))
 		return 0;
 
 	if (((__u64) es1->es_len) + es2->es_len > EXT_MAX_BLOCKS) {
@@ -425,6 +425,8 @@ ext4_es_try_to_merge_left(struct inode *inode, struct extent_status *es)
 	es1 = rb_entry(node, struct extent_status, rb_node);
 	if (ext4_es_can_be_merged(es1, es)) {
 		es1->es_len += es->es_len;
+		if (ext4_es_is_referenced(es))
+			ext4_es_set_referenced(es1);
 		rb_erase(&es->rb_node, &tree->root);
 		ext4_es_free_extent(inode, es);
 		es = es1;
@@ -447,6 +449,8 @@ ext4_es_try_to_merge_right(struct inode *inode, struct extent_status *es)
 	es1 = rb_entry(node, struct extent_status, rb_node);
 	if (ext4_es_can_be_merged(es, es1)) {
 		es->es_len += es1->es_len;
+		if (ext4_es_is_referenced(es1))
+			ext4_es_set_referenced(es);
 		rb_erase(node, &tree->root);
 		ext4_es_free_extent(inode, es1);
 	}
@@ -813,6 +817,8 @@ out:
 		es->es_lblk = es1->es_lblk;
 		es->es_len = es1->es_len;
 		es->es_pblk = es1->es_pblk;
+		if (!ext4_es_is_referenced(es))
+			ext4_es_set_referenced(es);
 		stats->es_stats_cache_hits++;
 	} else {
 		stats->es_stats_cache_misses++;
@@ -1252,11 +1258,17 @@ static int es_do_reclaim_extents(struct ext4_inode_info *ei, ext4_lblk_t end,
 		 * We can't reclaim delayed extent from status tree because
 		 * fiemap, bigallic, and seek_data/hole need to use it.
 		 */
-		if (!ext4_es_is_delayed(es)) {
-			rb_erase(&es->rb_node, &tree->root);
-			ext4_es_free_extent(inode, es);
-			(*nr_shrunk)++;
+		if (ext4_es_is_delayed(es))
+			goto next;
+		if (ext4_es_is_referenced(es)) {
+			ext4_es_clear_referenced(es);
+			goto next;
 		}
+
+		rb_erase(&es->rb_node, &tree->root);
+		ext4_es_free_extent(inode, es);
+		(*nr_shrunk)++;
+next:
 		if (!node)
 			goto out_wrap;
 		es = rb_entry(node, struct extent_status, rb_node);