linux-kernel - [PATCH v4] f2fs: avoid splitting bio when reading multiple pages

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Message-ID: <20250630125753.650630-1-huangjianan@xiaomi.com>
Date: Mon, 30 Jun 2025 20:57:53 +0800
From: Jianan Huang <huangjianan@...omi.com>
To: <linux-f2fs-devel@...ts.sourceforge.net>, <chao@...nel.org>,
	<jaegeuk@...nel.org>
CC: <wanghui33@...omi.com>, <linux-kernel@...r.kernel.org>, Jianan Huang
	<huangjianan@...omi.com>, Sheng Yong <shengyong1@...omi.com>
Subject: [PATCH v4] 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 <huangjianan@...omi.com>
Signed-off-by: Sheng Yong <shengyong1@...omi.com>
---
Changes since v3:
- Keep max_nr_pages unchanged across multiple reads.
Changes since v2:
- Initialize index only for compressed files.
Changes since v1:
- Use aligned nr_pages instead of nr_cpages to pre-allocate bvecs.

 fs/f2fs/data.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 31e892842625..40292e4ad341 100644
--- a/fs/f2fs/data.c
+++ b/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;
-- 
2.43.0