f2fs: avoid allocating failure in bio_alloc

This patch add macro MAX_BIO_BLOCKS to limit value of npages in
f2fs_bio_alloc, it can avoid allocating failure in bio_alloc caused by
npages is larger than BIO_MAX_PAGES.

Signed-off-by: Yu Chao <chao2.yu@samsung.com>
Reviewed-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index bdd10ea..7f94d78 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -90,6 +90,8 @@
 	(blk_addr << ((sbi)->log_blocksize - F2FS_LOG_SECTOR_SIZE))
 #define SECTOR_TO_BLOCK(sbi, sectors)					\
 	(sectors >> ((sbi)->log_blocksize - F2FS_LOG_SECTOR_SIZE))
+#define MAX_BIO_BLOCKS(max_hw_blocks)					\
+	(min((int)max_hw_blocks, BIO_MAX_PAGES))
 
 /* during checkpoint, bio_private is used to synchronize the last bio */
 struct bio_private {