blkcg: associate writeback bios with a blkg

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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 476722b..baf19bf 100644 (file)
--- 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 f0f069c..b42477b 100644 (file)
--- a/block/bio.c
+++ b/block/bio.c
@@ -2034,6 +2034,24 @@ 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)
+{
+       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 1286c2b..d60d61e 100644 (file)
--- 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(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 db75901..2aa62d5 100644 (file)
--- 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/bio.h b/include/linux/bio.h
index f13572c..f043806 100644 (file)
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -515,6 +515,8 @@ 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 */
@@ -522,6 +524,9 @@ 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 fdfd04e..738a0c2 100644 (file)
--- 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 */