f2fs: check the largest extent at look-up time

Because of the extent shrinker or other -ENOMEM scenarios, it cannot guarantee
that the largest extent would be cached in the tree all the time.

Instead of relying on extent_tree, we can simply check the cached one in extent
tree accordingly.

Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -512,12 +512,22 @@ static bool f2fs_lookup_extent_tree(struct inode *inode, pgoff_t pgofs,
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 	struct extent_tree *et = F2FS_I(inode)->extent_tree;
 	struct extent_node *en;
+	bool ret = false;
 
 	f2fs_bug_on(sbi, !et);
 
 	trace_f2fs_lookup_extent_tree_start(inode, pgofs);
 
 	read_lock(&et->lock);
+
+	if (et->largest.fofs <= pgofs &&
+			et->largest.fofs + et->largest.len > pgofs) {
+		*ei = et->largest;
+		ret = true;
+		stat_inc_read_hit(sbi->sb);
+		goto out;
+	}
+
 	en = __lookup_extent_tree(et, pgofs);
 	if (en) {
 		*ei = en->ei;
@@ -526,13 +536,15 @@ static bool f2fs_lookup_extent_tree(struct inode *inode, pgoff_t pgofs,
 			list_move_tail(&en->list, &sbi->extent_list);
 		et->cached_en = en;
 		spin_unlock(&sbi->extent_lock);
+		ret = true;
 		stat_inc_read_hit(sbi->sb);
 	}
+out:
 	stat_inc_total_hit(sbi->sb);
 	read_unlock(&et->lock);
 
-	trace_f2fs_lookup_extent_tree_end(inode, pgofs, en);
-	return en ? true : false;
+	trace_f2fs_lookup_extent_tree_end(inode, pgofs, ei);
+	return ret;
 }
 
 /* return true, if on-disk extent should be updated */

include/trace/events/f2fs.h

@@ -1099,11 +1099,11 @@ TRACE_EVENT(f2fs_lookup_extent_tree_start,
 TRACE_EVENT_CONDITION(f2fs_lookup_extent_tree_end,
 
 	TP_PROTO(struct inode *inode, unsigned int pgofs,
-						struct extent_node *en),
+						struct extent_info *ei),
 
-	TP_ARGS(inode, pgofs, en),
+	TP_ARGS(inode, pgofs, ei),
 
-	TP_CONDITION(en),
+	TP_CONDITION(ei),
 
 	TP_STRUCT__entry(
 		__field(dev_t,	dev)
@@ -1118,9 +1118,9 @@ TRACE_EVENT_CONDITION(f2fs_lookup_extent_tree_end,
 		__entry->dev = inode->i_sb->s_dev;
 		__entry->ino = inode->i_ino;
 		__entry->pgofs = pgofs;
-		__entry->fofs = en->ei.fofs;
-		__entry->blk = en->ei.blk;
-		__entry->len = en->ei.len;
+		__entry->fofs = ei->fofs;
+		__entry->blk = ei->blk;
+		__entry->len = ei->len;
 	),
 
 	TP_printk("dev = (%d,%d), ino = %lu, pgofs = %u, "