f2fs: let checkpoint flush dnode page of regular

Fsyncer will wait on all dnode pages of regular writeback before flushing,
if there are async dnode pages blocked by IO scheduler, it may decrease
fsync's performance.

In this patch, we choose to let f2fs_balance_fs_bg() to trigger checkpoint
to flush these dnode pages of regular, so async IO of dnode page can be
elimitnated, making fsyncer only need to wait for sync IO.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/node.c

@@ -1410,6 +1410,10 @@ static int __write_node_page(struct page *page, bool atomic, bool *submitted,
 	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
 		goto redirty_out;
 
+	if (wbc->sync_mode == WB_SYNC_NONE &&
+			IS_DNODE(page) && is_cold_node(page))
+		goto redirty_out;
+
 	/* get old block addr of this node page */
 	nid = nid_of_node(page);
 	f2fs_bug_on(sbi, page->index != nid);
@@ -1727,10 +1731,12 @@ int f2fs_sync_node_pages(struct f2fs_sb_info *sbi,
 	}
 
 	if (step < 2) {
+		if (wbc->sync_mode == WB_SYNC_NONE && step == 1)
+			goto out;
 		step++;
 		goto next_step;
 	}
-
+out:
 	if (nwritten)
 		f2fs_submit_merged_write(sbi, NODE);
 

fs/f2fs/node.h

@@ -135,6 +135,11 @@ static inline bool excess_cached_nats(struct f2fs_sb_info *sbi)
 	return NM_I(sbi)->nat_cnt >= DEF_NAT_CACHE_THRESHOLD;
 }
 
+static inline bool excess_dirty_nodes(struct f2fs_sb_info *sbi)
+{
+	return get_pages(sbi, F2FS_DIRTY_NODES) >= sbi->blocks_per_seg * 8;
+}
+
 enum mem_type {
 	FREE_NIDS,	/* indicates the free nid list */
 	NAT_ENTRIES,	/* indicates the cached nat entry */

fs/f2fs/segment.c

@@ -509,14 +509,16 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
 	else
 		f2fs_build_free_nids(sbi, false, false);
 
-	if (!is_idle(sbi) && !excess_dirty_nats(sbi))
+	if (!is_idle(sbi) &&
+		(!excess_dirty_nats(sbi) && !excess_dirty_nodes(sbi)))
 		return;
 
 	/* checkpoint is the only way to shrink partial cached entries */
 	if (!f2fs_available_free_memory(sbi, NAT_ENTRIES) ||
 			!f2fs_available_free_memory(sbi, INO_ENTRIES) ||
 			excess_prefree_segs(sbi) ||
 			excess_dirty_nats(sbi) ||
+			excess_dirty_nodes(sbi) ||
 			f2fs_time_over(sbi, CP_TIME)) {
 		if (test_opt(sbi, DATA_FLUSH)) {
 			struct blk_plug plug;