f2fs: avoid splitting bio when reading multiple pages

When fewer pages are read, nr_pages may be smaller than nr_cpages. Due
to the nr_vecs limit, the compressed pages will be split into multiple
bios and then merged at the block level. In this case, nr_cpages should
be used to pre-allocate bvecs.
To handle this case, align max_nr_pages to cluster_size, which should be
enough for all compressed pages.

Signed-off-by: Jianan Huang <[email protected]>
Signed-off-by: Sheng Yong <[email protected]>
Reviewed-by: Chao Yu <[email protected]>
Signed-off-by: Jaegeuk Kim <[email protected]>

Author: mofishzz

fs/f2fs/data.c

@@ -2303,7 +2303,7 @@ int f2fs_read_multi_pages(struct compress_ctx *cc, struct bio **bio_ret,
 		}
 
 		if (!bio) {
-			bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages,
+			bio = f2fs_grab_read_bio(inode, blkaddr, nr_pages - i,
 					f2fs_ra_op_flags(rac),
 					folio->index, for_write);
 			if (IS_ERR(bio)) {
@@ -2376,6 +2376,14 @@ static int f2fs_mpage_readpages(struct inode *inode,
 	unsigned max_nr_pages = nr_pages;
 	int ret = 0;
 
+#ifdef CONFIG_F2FS_FS_COMPRESSION
+	if (f2fs_compressed_file(inode)) {
+		index = rac ? readahead_index(rac) : folio->index;
+		max_nr_pages = round_up(index + nr_pages, cc.cluster_size) -
+				round_down(index, cc.cluster_size);
+	}
+#endif
+
 	map.m_pblk = 0;
 	map.m_lblk = 0;
 	map.m_len = 0;