[PATCH 43/45] buffer, writeback: make __block_write_full_page() honor cgroup writeback

[Tejun Heo]

[__]block_write_full_page() is used to implement ->writepage in
various filesystems.  All writeback logic is now updated to handle
cgroup writeback and the block cgroup to issue IOs for is encoded in
writeback_control and can be retrieved using wbc_blkcg_css(); however,
[__]block_write_full_page() currently ignores the blkcg indicated by
wbc and issues all bio's without explicit blkcg association.

This patch adds submit_bh_blkcg() which associates the bio with the
specified blkio cgroup before issuing and uses it in
__block_write_full_page() so that the issued bio's are associated with
wbc_blkcg_css().

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
 fs/buffer.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 2dab7dd..1377346 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -45,6 +45,9 @@
 #include <trace/events/block.h>
 
 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
+static int submit_bh_blkcg(int rw, struct buffer_head *bh,
+			   unsigned long bio_flags,
+			   struct cgroup_subsys_state *blkcg_css);
 
 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
 
@@ -1777,7 +1780,7 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
 	do {
 		struct buffer_head *next = bh->b_this_page;
 		if (buffer_async_write(bh)) {
-			submit_bh(write_op, bh);
+			submit_bh_blkcg(write_op, bh, 0, wbc_blkcg_css(wbc));
 			nr_underway++;
 		}
 		bh = next;
@@ -1831,7 +1834,7 @@ recover:
 		struct buffer_head *next = bh->b_this_page;
 		if (buffer_async_write(bh)) {
 			clear_buffer_dirty(bh);
-			submit_bh(write_op, bh);
+			submit_bh_blkcg(write_op, bh, 0, wbc_blkcg_css(wbc));
 			nr_underway++;
 		}
 		bh = next;
@@ -3000,7 +3003,9 @@ void guard_bio_eod(int rw, struct bio *bio)
 	}
 }
 
-int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags)
+static int submit_bh_blkcg(int rw, struct buffer_head *bh,
+			   unsigned long bio_flags,
+			   struct cgroup_subsys_state *blkcg_css)
 {
 	struct bio *bio;
 	int ret = 0;
@@ -3023,6 +3028,9 @@ int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags)
 	 */
 	bio = bio_alloc(GFP_NOIO, 1);
 
+	if (blkcg_css)
+		bio_associate_blkcg(bio, blkcg_css);
+
 	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
 	bio->bi_bdev = bh->b_bdev;
 	bio->bi_io_vec[0].bv_page = bh->b_page;
@@ -3053,11 +3061,16 @@ int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags)
 	bio_put(bio);
 	return ret;
 }
+
+int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags)
+{
+	return submit_bh_blkcg(rw, bh, bio_flags, NULL);
+}
 EXPORT_SYMBOL_GPL(_submit_bh);
 
 int submit_bh(int rw, struct buffer_head *bh)
 {
-	return _submit_bh(rw, bh, 0);
+	return submit_bh_blkcg(rw, bh, 0, NULL);
 }
 EXPORT_SYMBOL(submit_bh);
 
-- 
2.1.0

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