[PATCH v2 3/7] fs: use on-stack-bio if backing device has BDI_CAP_SYNCHRONOUS capability

[Minchan Kim]

There is no need to use dynamic bio allocation for BDI_CAP_SYNCHRONOUS
devices. They can with on-stack bio without concern about waiting
bio allocation from mempool under heavy memory pressure.

Cc: Matthew Wilcox 
Signed-off-by: Minchan Kim 
---

Hi Mattew,

I didn't use sbvec[nr_pages] as you suggested[1] because I don't think
it's pointless in do_mpage_readpage which works per-page base as
I replied to you.
If I misunderstood something, please correct me.

[1] http://lkml.kernel.org/r/<20170808132904.gc31...@bombadil.infradead.org>

 fs/mpage.c | 47 ---
 1 file changed, 40 insertions(+), 7 deletions(-)

diff --git a/fs/mpage.c b/fs/mpage.c
index 2e4c41ccb5c9..d3b777fdfd5a 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -162,6 +162,9 @@ do_mpage_readpage(struct bio *bio, struct page *page, 
unsigned nr_pages,
int fully_mapped = 1;
unsigned nblocks;
unsigned relative_block;
+   /* on-stack bio for synchronous devices */
+   struct bio sbio;
+   struct bio_vec sbvec;
 
if (page_has_buffers(page))
goto confused;
@@ -282,10 +285,22 @@ do_mpage_readpage(struct bio *bio, struct page *page, 
unsigned nr_pages,
page))
goto out;
}
-   bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
+
+   if (bdi_cap_synchronous_io(inode_to_bdi(inode))) {
+   bio = 
+   /* mpage_end_io calls bio_put unconditionally */
+   bio_get();
+
+   bio_init(, , 1);
+   sbio.bi_bdev = bdev;
+   sbio.bi_iter.bi_sector = blocks[0] << (blkbits - 9);
+   } else {
+
+   bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
min_t(int, nr_pages, BIO_MAX_PAGES), gfp);
-   if (bio == NULL)
-   goto confused;
+   if (bio == NULL)
+   goto confused;
+   }
}
 
length = first_hole << blkbits;
@@ -302,6 +317,8 @@ do_mpage_readpage(struct bio *bio, struct page *page, 
unsigned nr_pages,
else
*last_block_in_bio = blocks[blocks_per_page - 1];
 out:
+   if (bio == )
+   bio = mpage_bio_submit(REQ_OP_READ, 0, bio);
return bio;
 
 confused:
@@ -492,6 +509,9 @@ static int __mpage_writepage(struct page *page, struct 
writeback_control *wbc,
loff_t i_size = i_size_read(inode);
int ret = 0;
int op_flags = wbc_to_write_flags(wbc);
+   /* on-stack-bio */
+   struct bio sbio;
+   struct bio_vec sbvec;
 
if (page_has_buffers(page)) {
struct buffer_head *head = page_buffers(page);
@@ -610,10 +630,21 @@ static int __mpage_writepage(struct page *page, struct 
writeback_control *wbc,
goto out;
}
}
-   bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
-   BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH);
-   if (bio == NULL)
-   goto confused;
+
+   if (bdi_cap_synchronous_io(inode_to_bdi(inode))) {
+   bio = 
+   /* mpage_end_io calls bio_put unconditionally */
+   bio_get();
+
+   bio_init(, , 1);
+   sbio.bi_bdev = bdev;
+   sbio.bi_iter.bi_sector = blocks[0] << (blkbits - 9);
+   } else {
+   bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
+   BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH);
+   if (bio == NULL)
+   goto confused;
+   }
 
wbc_init_bio(wbc, bio);
bio->bi_write_hint = inode->i_write_hint;
@@ -662,6 +693,8 @@ static int __mpage_writepage(struct page *page, struct 
writeback_control *wbc,
 */
mapping_set_error(mapping, ret);
 out:
+   if (bio == )
+   bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
mpd->bio = bio;
return ret;
 }
-- 
2.7.4

[PATCH v2 3/7] fs: use on-stack-bio if backing device has BDI_CAP_SYNCHRONOUS capability

[Minchan Kim]

There is no need to use dynamic bio allocation for BDI_CAP_SYNCHRONOUS
devices. They can with on-stack bio without concern about waiting
bio allocation from mempool under heavy memory pressure.

Cc: Matthew Wilcox 
Signed-off-by: Minchan Kim 
---

Hi Mattew,

I didn't use sbvec[nr_pages] as you suggested[1] because I don't think
it's pointless in do_mpage_readpage which works per-page base as
I replied to you.
If I misunderstood something, please correct me.

[1] http://lkml.kernel.org/r/<20170808132904.gc31...@bombadil.infradead.org>

 fs/mpage.c | 47 ---
 1 file changed, 40 insertions(+), 7 deletions(-)

diff --git a/fs/mpage.c b/fs/mpage.c
index 2e4c41ccb5c9..d3b777fdfd5a 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -162,6 +162,9 @@ do_mpage_readpage(struct bio *bio, struct page *page, 
unsigned nr_pages,
int fully_mapped = 1;
unsigned nblocks;
unsigned relative_block;
+   /* on-stack bio for synchronous devices */
+   struct bio sbio;
+   struct bio_vec sbvec;
 
if (page_has_buffers(page))
goto confused;
@@ -282,10 +285,22 @@ do_mpage_readpage(struct bio *bio, struct page *page, 
unsigned nr_pages,
page))
goto out;
}
-   bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
+
+   if (bdi_cap_synchronous_io(inode_to_bdi(inode))) {
+   bio = 
+   /* mpage_end_io calls bio_put unconditionally */
+   bio_get();
+
+   bio_init(, , 1);
+   sbio.bi_bdev = bdev;
+   sbio.bi_iter.bi_sector = blocks[0] << (blkbits - 9);
+   } else {
+
+   bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
min_t(int, nr_pages, BIO_MAX_PAGES), gfp);
-   if (bio == NULL)
-   goto confused;
+   if (bio == NULL)
+   goto confused;
+   }
}
 
length = first_hole << blkbits;
@@ -302,6 +317,8 @@ do_mpage_readpage(struct bio *bio, struct page *page, 
unsigned nr_pages,
else
*last_block_in_bio = blocks[blocks_per_page - 1];
 out:
+   if (bio == )
+   bio = mpage_bio_submit(REQ_OP_READ, 0, bio);
return bio;
 
 confused:
@@ -492,6 +509,9 @@ static int __mpage_writepage(struct page *page, struct 
writeback_control *wbc,
loff_t i_size = i_size_read(inode);
int ret = 0;
int op_flags = wbc_to_write_flags(wbc);
+   /* on-stack-bio */
+   struct bio sbio;
+   struct bio_vec sbvec;
 
if (page_has_buffers(page)) {
struct buffer_head *head = page_buffers(page);
@@ -610,10 +630,21 @@ static int __mpage_writepage(struct page *page, struct 
writeback_control *wbc,
goto out;
}
}
-   bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
-   BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH);
-   if (bio == NULL)
-   goto confused;
+
+   if (bdi_cap_synchronous_io(inode_to_bdi(inode))) {
+   bio = 
+   /* mpage_end_io calls bio_put unconditionally */
+   bio_get();
+
+   bio_init(, , 1);
+   sbio.bi_bdev = bdev;
+   sbio.bi_iter.bi_sector = blocks[0] << (blkbits - 9);
+   } else {
+   bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
+   BIO_MAX_PAGES, GFP_NOFS|__GFP_HIGH);
+   if (bio == NULL)
+   goto confused;
+   }
 
wbc_init_bio(wbc, bio);
bio->bi_write_hint = inode->i_write_hint;
@@ -662,6 +693,8 @@ static int __mpage_writepage(struct page *page, struct 
writeback_control *wbc,
 */
mapping_set_error(mapping, ret);
 out:
+   if (bio == )
+   bio = mpage_bio_submit(REQ_OP_WRITE, op_flags, bio);
mpd->bio = bio;
return ret;
 }
-- 
2.7.4