linux-kernel - [PATCH] bio: limit bio max size.

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Date:   Tue, 12 Jan 2021 17:33:11 +0900
From:   Changheun Lee <nanich.lee@...sung.com>
To:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        axboe@...nel.dk, johannes.thumshirn@....com, tj@...nel.org
Cc:     seunghwan.hyun@...sung.com, sookwan7.kim@...sung.com,
        yt0928.kim@...sung.com, mj0123.lee@...sung.com,
        junho89.kim@...sung.com, jisoo2146.oh@...sung.com,
        "Changheun Lee" <nanich.lee@...sung.com>
Subject: [PATCH] bio: limit bio max size.

From: "Changheun Lee" <nanich.lee@...sung.com>

bio size can grow up to 4GB when muli-page bvec is enabled.
but sometimes it would lead to inefficient behaviors.
in case of large chunk direct I/O, - 64MB chunk read in user space -
all pages for 64MB would be merged to a bio structure if memory address is
continued phsycally. it makes some delay to submit until merge complete.
bio max size should be limited as a proper size.

Signed-off-by: Changheun Lee <nanich.lee@...sung.com>
---
 block/bio.c         | 2 +-
 include/linux/bio.h | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 1f2cc1fbe283..dbe14d675f28 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -877,7 +877,7 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
 		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
 
 		if (page_is_mergeable(bv, page, len, off, same_page)) {
-			if (bio->bi_iter.bi_size > UINT_MAX - len) {
+			if (bio->bi_iter.bi_size > BIO_MAX_SIZE - len) {
 				*same_page = false;
 				return false;
 			}
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 1edda614f7ce..0f49b354b1f6 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -20,6 +20,7 @@
 #endif
 
 #define BIO_MAX_PAGES		256
+#define BIO_MAX_SIZE		(BIO_MAX_PAGES * PAGE_SIZE)
 
 #define bio_prio(bio)			(bio)->bi_ioprio
 #define bio_set_prio(bio, prio)		((bio)->bi_ioprio = prio)
@@ -113,7 +114,7 @@ static inline bool bio_full(struct bio *bio, unsigned len)
 	if (bio->bi_vcnt >= bio->bi_max_vecs)
 		return true;
 
-	if (bio->bi_iter.bi_size > UINT_MAX - len)
+	if (bio->bi_iter.bi_size > BIO_MAX_SIZE - len)
 		return true;
 
 	return false;
-- 
2.28.0