f2fs: avoid small data writes by skipping writepages

This patch introduces nr_pages_to_skip(sbi, type) to determine writepages can
be skipped.
The dentry, node, and meta pages can be conrolled by F2FS without breaking the
FS consistency.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/checkpoint.c

@@ -187,7 +187,7 @@ static int f2fs_write_meta_pages(struct address_space *mapping,
 				struct writeback_control *wbc)
 {
 	struct f2fs_sb_info *sbi = F2FS_SB(mapping->host->i_sb);
-	int nrpages = MAX_BIO_BLOCKS(max_hw_blocks(sbi));
+	int nrpages = nr_pages_to_skip(sbi, META);
 	long written;
 
 	if (wbc->for_kupdate)
@@ -682,7 +682,7 @@ retry:
 	inode = igrab(entry->inode);
 	spin_unlock(&sbi->dir_inode_lock);
 	if (inode) {
-		filemap_flush(inode->i_mapping);
+		filemap_fdatawrite(inode->i_mapping);
 		iput(inode);
 	} else {
 		/*

fs/f2fs/data.c

@@ -868,6 +868,10 @@ static int f2fs_write_data_pages(struct address_space *mapping,
 	if (!mapping->a_ops->writepage)
 		return 0;
 
+	if (S_ISDIR(inode->i_mode) && wbc->sync_mode == WB_SYNC_NONE &&
+			get_dirty_dents(inode) < nr_pages_to_skip(sbi, DATA))
+		return 0;
+
 	if (wbc->nr_to_write < MAX_DESIRED_PAGES_WP) {
 		desired_nrtw = MAX_DESIRED_PAGES_WP;
 		excess_nrtw = desired_nrtw - wbc->nr_to_write;

fs/f2fs/node.c

@@ -1198,12 +1198,6 @@ redirty_out:
 	return AOP_WRITEPAGE_ACTIVATE;
 }
 
-/*
- * It is very important to gather dirty pages and write at once, so that we can
- * submit a big bio without interfering other data writes.
- * Be default, 512 pages (2MB) * 3 node types, is more reasonable.
- */
-#define COLLECT_DIRTY_NODES	1536
 static int f2fs_write_node_pages(struct address_space *mapping,
 			    struct writeback_control *wbc)
 {
@@ -1214,7 +1208,7 @@ static int f2fs_write_node_pages(struct address_space *mapping,
 	f2fs_balance_fs_bg(sbi);
 
 	/* collect a number of dirty node pages and write together */
-	if (get_pages(sbi, F2FS_DIRTY_NODES) < COLLECT_DIRTY_NODES)
+	if (get_pages(sbi, F2FS_DIRTY_NODES) < nr_pages_to_skip(sbi, NODE))
 		return 0;
 
 	/* if mounting is failed, skip writing node pages */

fs/f2fs/segment.h

@@ -664,3 +664,22 @@ static inline unsigned int max_hw_blocks(struct f2fs_sb_info *sbi)
 	struct request_queue *q = bdev_get_queue(bdev);
 	return SECTOR_TO_BLOCK(sbi, queue_max_sectors(q));
 }
+
+/*
+ * It is very important to gather dirty pages and write at once, so that we can
+ * submit a big bio without interfering other data writes.
+ * By default, 512 pages for directory data,
+ * 512 pages (2MB) * 3 for three types of nodes, and
+ * max_bio_blocks for meta are set.
+ */
+static inline int nr_pages_to_skip(struct f2fs_sb_info *sbi, int type)
+{
+	if (type == DATA)
+		return sbi->blocks_per_seg;
+	else if (type == NODE)
+		return 3 * sbi->blocks_per_seg;
+	else if (type == META)
+		return MAX_BIO_BLOCKS(max_hw_blocks(sbi));
+	else
+		return 0;
+}