[PATCH 09/15] blkcg: associate writeback bios with a blkg

Dennis Zhou
2018-08-31T01:53:50Z

From: "Dennis Zhou (Facebook)" <dennisszhou@gmail.com>

One of the goals of this series is to remove a separate reference to
the css of the bio. This can and should be accessed via bio_blkcg. In
this patch, the wbc_init_bio call is changed such that it must be called
after a queue has been associated with the bio.

Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
---
Documentation/admin-guide/cgroup-v2.rst | 8 +++++---
fs/buffer.c | 10 +++++-----
fs/ext4/page-io.c | 2 +-
include/linux/writeback.h | 5 +++--
4 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 1746131bc9cb..2dc8f95077aa 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1839,8 +1839,10 @@ following two functions.

wbc_init_bio(@wbc, @bio)
Should be called for each bio carrying writeback data and
- associates the bio with the inode's owner cgroup. Can be
- called anytime between bio allocation and submission.
+ associates the bio with the inode's owner cgroup and the
+ corresponding request queue. This must be called after
+ a queue (device) has been associated with the bio and
+ before submission.

wbc_account_io(@wbc, @page, @bytes)
Should be called for each data segment being written out.
@@ -1859,7 +1861,7 @@ the configuration, the bio may be executed at a lower priority and if
the writeback session is holding shared resources, e.g. a journal
entry, may lead to priority inversion. There is no one easy solution
for the problem. Filesystems can try to work around specific problem
-cases by skipping wbc_init_bio() or using bio_associate_blkcg()
+cases by skipping wbc_init_bio() or using bio_associate_create_blkg()
directly.

diff --git a/fs/buffer.c b/fs/buffer.c
index cabc045f483d..7fb8adb44583 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3049,11 +3049,6 @@ static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
*/
bio = bio_alloc(GFP_NOIO, 1);

- if (wbc) {
- wbc_init_bio(wbc, bio);
- wbc_account_io(wbc, bh->b_page, bh->b_size);
- }
-
bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
bio_set_dev(bio, bh->b_bdev);
bio->bi_write_hint = write_hint;
@@ -3073,6 +3068,11 @@ static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
op_flags |= REQ_PRIO;
bio_set_op_attrs(bio, op, op_flags);

+ if (wbc) {
+ wbc_init_bio(wbc, bio);
+ wbc_account_io(wbc, bh->b_page, bh->b_size);
+ }
+
submit_bio(bio);
return 0;
}
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index db7590178dfc..2aa62d58d8dd 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -374,13 +374,13 @@ static int io_submit_init_bio(struct ext4_io_submit *io,
bio = bio_alloc(GFP_NOIO, BIO_MAX_PAGES);
if (!bio)
return -ENOMEM;
- wbc_init_bio(io->io_wbc, bio);
bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
bio_set_dev(bio, bh->b_bdev);
bio->bi_end_io = ext4_end_bio;
bio->bi_private = ext4_get_io_end(io->io_end);
io->io_bio = bio;
io->io_next_block = bh->b_blocknr;
+ wbc_init_bio(io->io_wbc, bio);
return 0;
}

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index fdfd04e348f6..738a0c24874f 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -246,7 +246,8 @@ static inline void wbc_attach_fdatawrite_inode(struct writeback_control *wbc,
*
* @bio is a part of the writeback in progress controlled by @wbc. Perform
* writeback specific initialization. This is used to apply the cgroup
- * writeback context.
+ * writeback context. Must be called after the bio has been associated with
+ * a device.
*/
static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
{
@@ -257,7 +258,7 @@ static inline void wbc_init_bio(struct writeback_control *wbc, struct bio *bio)
* regular writeback instead of writing things out itself.
*/
if (wbc->wb)
- bio_associate_blkcg(bio, wbc->wb->blkcg_css);
+ bio_associate_blkg_from_css(bio, wbc->wb->blkcg_css);
}

#else /* CONFIG_CGROUP_WRITEBACK */
--
2.17.1