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Subject[PATCH 08/13] blkcg: associate writeback bios with a blkg
Date
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, wbc_init_bio() now requires a bio to have a device
associated with it.

Signed-off-by: Dennis Zhou <dennis@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Acked-by: Tejun Heo <tj@kernel.org>
---
Documentation/admin-guide/cgroup-v2.rst | 8 +++++---
block/bio.c | 21 +++++++++++++++++++++
fs/buffer.c | 10 +++++-----
fs/ext4/page-io.c | 2 +-
include/linux/bio.h | 5 +++++
include/linux/writeback.h | 5 +++--
6 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 476722b7b636..baf19bf28385 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1879,8 +1879,10 @@ 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.
@@ -1899,7 +1901,7 @@ 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() and using bio_associate_blkg()
directly.


diff --git a/block/bio.c b/block/bio.c
index 4600808ac606..e9e930b6a10c 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -2048,6 +2048,27 @@ static void __bio_associate_blkg_from_css(struct bio *bio,
rcu_read_unlock();
}

+/**
+ * bio_associate_blkg_from_css - associate a bio with a specified css
+ * @bio: target bio
+ * @css: target css
+ *
+ * Associate @bio with the blkg found by combining the css's blkg and the
+ * request_queue of the @bio. This takes a reference on the css that will
+ * be put upon freeing of @bio.
+ */
+void bio_associate_blkg_from_css(struct bio *bio,
+ struct cgroup_subsys_state *css)
+{
+ if (!bio_has_queue(bio))
+ return;
+
+ css_get(css);
+ bio->bi_css = css;
+ __bio_associate_blkg_from_css(bio, css);
+}
+EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);
+
#ifdef CONFIG_MEMCG
/**
* bio_associate_blkg_from_page - associate a bio with the page's blkg
diff --git a/fs/buffer.c b/fs/buffer.c
index 9661e5be87e2..45452bd55c8e 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3060,11 +3060,6 @@ 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_only(bio, bh->b_bdev);
bio->bi_write_hint = write_hint;
@@ -3084,6 +3079,11 @@ 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 cadf91a42fa5..ab383085fb5e 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_only(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/bio.h b/include/linux/bio.h
index ad322232db3e..a9958f2bcb48 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -520,6 +520,8 @@ static inline void bio_associate_blkg_from_page(struct bio *bio,
int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css);
void bio_disassociate_blkg(struct bio *bio);
void bio_associate_blkg(struct bio *bio);
+void bio_associate_blkg_from_css(struct bio *bio,
+ struct cgroup_subsys_state *css);
void bio_disassociate_task(struct bio *bio);
void bio_clone_blkcg_association(struct bio *dst, struct bio *src);
#else /* CONFIG_BLK_CGROUP */
@@ -527,6 +529,9 @@ static inline int bio_associate_blkcg(struct bio *bio,
struct cgroup_subsys_state *blkcg_css) { return 0; }
static inline void bio_disassociate_blkg(struct bio *bio) { }
static inline void bio_associate_blkg(struct bio *bio) { }
+static inline void bio_associate_blkg_from_css(struct bio *bio,
+ struct cgroup_subsys_state *css)
+{ }
static inline void bio_disassociate_task(struct bio *bio) { }
static inline void bio_clone_blkcg_association(struct bio *dst,
struct bio *src) { }
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
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