f2fs: shrink nat_cache entries

This patch registers shrinking nat_cache entries.
Reviewed-by: NChao Yu <chao2.yu@samsung.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/node.c

@@ -328,11 +328,11 @@ static void set_node_addr(struct f2fs_sb_info *sbi, struct node_info *ni,
 int try_to_free_nats(struct f2fs_sb_info *sbi, int nr_shrink)
 {
 	struct f2fs_nm_info *nm_i = NM_I(sbi);
+	int nr = nr_shrink;
 
-	if (available_free_memory(sbi, NAT_ENTRIES))
+	if (!down_write_trylock(&nm_i->nat_tree_lock))
 		return 0;
 
-	down_write(&nm_i->nat_tree_lock);
 	while (nr_shrink && !list_empty(&nm_i->nat_entries)) {
 		struct nat_entry *ne;
 		ne = list_first_entry(&nm_i->nat_entries,
@@ -341,7 +341,7 @@ int try_to_free_nats(struct f2fs_sb_info *sbi, int nr_shrink)
 		nr_shrink--;
 	}
 	up_write(&nm_i->nat_tree_lock);
-	return nr_shrink;
+	return nr - nr_shrink;
 }
 
 /*

fs/f2fs/segment.c

@@ -306,8 +306,12 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
 	/* try to shrink extent cache when there is no enough memory */
 	f2fs_shrink_extent_tree(sbi, EXTENT_CACHE_SHRINK_NUMBER);
 
-	/* check the # of cached NAT entries and prefree segments */
-	if (try_to_free_nats(sbi, NAT_ENTRY_PER_BLOCK) ||
+	/* check the # of cached NAT entries */
+	if (!available_free_memory(sbi, NAT_ENTRIES))
+		try_to_free_nats(sbi, NAT_ENTRY_PER_BLOCK);
+
+	/* checkpoint is the only way to shrink partial cached entries */
+	if (!available_free_memory(sbi, NAT_ENTRIES) ||
 			excess_prefree_segs(sbi) ||
 			!available_free_memory(sbi, INO_ENTRIES))
 		f2fs_sync_fs(sbi->sb, true);

fs/f2fs/shrinker.c

@@ -18,6 +18,11 @@ static LIST_HEAD(f2fs_list);
 static DEFINE_SPINLOCK(f2fs_list_lock);
 static unsigned int shrinker_run_no;
 
+static unsigned long __count_nat_entries(struct f2fs_sb_info *sbi)
+{
+	return NM_I(sbi)->nat_cnt - NM_I(sbi)->dirty_nat_cnt;
+}
+
 unsigned long f2fs_shrink_count(struct shrinker *shrink,
 				struct shrink_control *sc)
 {
@@ -37,7 +42,8 @@ unsigned long f2fs_shrink_count(struct shrinker *shrink,
 		}
 		spin_unlock(&f2fs_list_lock);
 
-		/* TODO: count # of objects */
+		/* shrink clean nat cache entries */
+		count += __count_nat_entries(sbi);
 
 		spin_lock(&f2fs_list_lock);
 		p = p->next;
@@ -76,7 +82,8 @@ unsigned long f2fs_shrink_scan(struct shrinker *shrink,
 
 		sbi->shrinker_run_no = run_no;
 
-		/* TODO: shrink caches */
+		/* shrink clean nat cache entries */
+		freed += try_to_free_nats(sbi, nr);
 
 		spin_lock(&f2fs_list_lock);
 		p = p->next;