f2fs: avoid unnecessary bio submit when wait page writeback

This patch introduce is_merged_page() to check whether current page is merged
in f2fs bio cache. When page is not in cache, we can avoid submitting bio cache,
resulting in having more chance to merge pages.

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

fs/f2fs/data.c

@@ -134,7 +134,7 @@ void f2fs_submit_merged_bio(struct f2fs_sb_info *sbi,
 
 	io = is_read_io(rw) ? &sbi->read_io : &sbi->write_io[btype];
 
-	mutex_lock(&io->io_mutex);
+	down_write(&io->io_rwsem);
 
 	/* change META to META_FLUSH in the checkpoint procedure */
 	if (type >= META_FLUSH) {
@@ -142,7 +142,7 @@ void f2fs_submit_merged_bio(struct f2fs_sb_info *sbi,
 		io->fio.rw = WRITE_FLUSH_FUA | REQ_META | REQ_PRIO;
 	}
 	__submit_merged_bio(io);
-	mutex_unlock(&io->io_mutex);
+	up_write(&io->io_rwsem);
 }
 
 /*
@@ -180,7 +180,7 @@ void f2fs_submit_page_mbio(struct f2fs_sb_info *sbi, struct page *page,
 
 	verify_block_addr(sbi, blk_addr);
 
-	mutex_lock(&io->io_mutex);
+	down_write(&io->io_rwsem);
 
 	if (!is_read)
 		inc_page_count(sbi, F2FS_WRITEBACK);
@@ -204,7 +204,7 @@ alloc_new:
 
 	io->last_block_in_bio = blk_addr;
 
-	mutex_unlock(&io->io_mutex);
+	up_write(&io->io_rwsem);
 	trace_f2fs_submit_page_mbio(page, fio->rw, fio->type, blk_addr);
 }
 

fs/f2fs/f2fs.h

@@ -394,7 +394,7 @@ struct f2fs_bio_info {
 	struct bio *bio;		/* bios to merge */
 	sector_t last_block_in_bio;	/* last block number */
 	struct f2fs_io_info fio;	/* store buffered io info. */
-	struct mutex io_mutex;		/* mutex for bio */
+	struct rw_semaphore io_rwsem;	/* blocking op for bio */
 };
 
 struct f2fs_sb_info {

fs/f2fs/segment.c

@@ -1046,12 +1046,38 @@ void rewrite_node_page(struct f2fs_sb_info *sbi,
 	mutex_unlock(&curseg->curseg_mutex);
 }
 
+static inline bool is_merged_page(struct f2fs_sb_info *sbi,
+					struct page *page, enum page_type type)
+{
+	enum page_type btype = PAGE_TYPE_OF_BIO(type);
+	struct f2fs_bio_info *io = &sbi->write_io[btype];
+	struct bio *bio = io->bio;
+	struct bio_vec *bvec;
+	int i;
+
+	down_read(&io->io_rwsem);
+	if (!bio)
+		goto out;
+
+	bio_for_each_segment_all(bvec, bio, i) {
+		if (page == bvec->bv_page) {
+			up_read(&io->io_rwsem);
+			return true;
+		}
+	}
+
+out:
+	up_read(&io->io_rwsem);
+	return false;
+}
+
 void f2fs_wait_on_page_writeback(struct page *page,
 				enum page_type type)
 {
 	struct f2fs_sb_info *sbi = F2FS_SB(page->mapping->host->i_sb);
 	if (PageWriteback(page)) {
-		f2fs_submit_merged_bio(sbi, type, WRITE);
+		if (is_merged_page(sbi, page, type))
+			f2fs_submit_merged_bio(sbi, type, WRITE);
 		wait_on_page_writeback(page);
 	}
 }

fs/f2fs/super.c

@@ -920,11 +920,11 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	sbi->por_doing = false;
 	spin_lock_init(&sbi->stat_lock);
 
-	mutex_init(&sbi->read_io.io_mutex);
+	init_rwsem(&sbi->read_io.io_rwsem);
 	sbi->read_io.sbi = sbi;
 	sbi->read_io.bio = NULL;
 	for (i = 0; i < NR_PAGE_TYPE; i++) {
-		mutex_init(&sbi->write_io[i].io_mutex);
+		init_rwsem(&sbi->write_io[i].io_rwsem);
 		sbi->write_io[i].sbi = sbi;
 		sbi->write_io[i].bio = NULL;
 	}