f2fs: reuse nids more aggressively

If we can reuse nids as many as possible, we can mitigate producing obsolete
node pages in the page cache.
Reviewed-by: NChao Yu <chao2.yu@samsung.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/node.c

@@ -306,6 +306,10 @@ static void set_node_addr(struct f2fs_sb_info *sbi, struct node_info *ni,
 	if (nat_get_blkaddr(e) != NEW_ADDR && new_blkaddr == NULL_ADDR) {
 		unsigned char version = nat_get_version(e);
 		nat_set_version(e, inc_node_version(version));
+
+		/* in order to reuse the nid */
+		if (nm_i->next_scan_nid > ni->nid)
+			nm_i->next_scan_nid = ni->nid;
 	}
 
 	/* change address */