[PATCH] bio: limit bio max size.

[Changheun Lee]

From: "Changheun Lee" <nanich....@samsung.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....@samsung.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