f2fs: add a new function to support for merging contiguous read

For better read performance, we add a new function to support for merging
contiguous read as the one for write.

v1-->v2:
 o add declarations here as Gu Zheng suggested.
 o use new structure f2fs_bio_info introduced by Jaegeuk Kim.
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Acked-by: Gu Zheng <guz.fnst@cn.fujitsu.com>

fs/f2fs/data.c

@@ -414,6 +414,56 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
 	return 0;
 }
 
+void f2fs_submit_read_bio(struct f2fs_sb_info *sbi, int rw)
+{
+	struct f2fs_bio_info *io = &sbi->read_io;
+
+	if (!io->bio)
+		return;
+
+	mutex_lock(&io->io_mutex);
+	if (io->bio) {
+		submit_bio(rw, io->bio);
+		io->bio = NULL;
+	}
+	mutex_unlock(&io->io_mutex);
+}
+
+void submit_read_page(struct f2fs_sb_info *sbi, struct page *page,
+					block_t blk_addr, int rw)
+{
+	struct block_device *bdev = sbi->sb->s_bdev;
+	struct f2fs_bio_info *io = &sbi->read_io;
+	int bio_blocks;
+
+	verify_block_addr(sbi, blk_addr);
+
+	mutex_lock(&io->io_mutex);
+
+	if (io->bio && io->last_block_in_bio != blk_addr - 1) {
+		submit_bio(rw, io->bio);
+		io->bio = NULL;
+	}
+alloc_new:
+	if (io->bio == NULL) {
+		bio_blocks = MAX_BIO_BLOCKS(max_hw_blocks(sbi));
+		io->bio = f2fs_bio_alloc(bdev, bio_blocks);
+		io->bio->bi_sector = SECTOR_FROM_BLOCK(sbi, blk_addr);
+		io->bio->bi_end_io = read_end_io;
+	}
+
+	if (bio_add_page(io->bio, page, PAGE_CACHE_SIZE, 0) <
+							PAGE_CACHE_SIZE) {
+		submit_bio(rw, io->bio);
+		io->bio = NULL;
+		goto alloc_new;
+	}
+
+	io->last_block_in_bio = blk_addr;
+
+	mutex_unlock(&io->io_mutex);
+}
+
 /*
  * This function should be used by the data read flow only where it
  * does not check the "create" flag that indicates block allocation.

fs/f2fs/f2fs.h

@@ -382,6 +382,7 @@ struct f2fs_sb_info {
 	struct f2fs_sm_info *sm_info;		/* segment manager */
 
 	/* for bio operations */
+	struct f2fs_bio_info read_io;			/* for read bios */
 	struct f2fs_bio_info write_io[NR_PAGE_TYPE];	/* for write bios */
 
 	/* for checkpoint */
@@ -1132,6 +1133,8 @@ struct page *find_data_page(struct inode *, pgoff_t, bool);
 struct page *get_lock_data_page(struct inode *, pgoff_t);
 struct page *get_new_data_page(struct inode *, struct page *, pgoff_t, bool);
 int f2fs_readpage(struct f2fs_sb_info *, struct page *, block_t, int);
+void f2fs_submit_read_bio(struct f2fs_sb_info *, int);
+void submit_read_page(struct f2fs_sb_info *, struct page *, block_t, int);
 int do_write_data_page(struct page *);
 
 /*

fs/f2fs/super.c

@@ -878,6 +878,7 @@ 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);
 	for (i = 0; i < NR_PAGE_TYPE; i++)
 		mutex_init(&sbi->write_io[i].io_mutex);