[PATCH] blkcg: correctly update stat

[PATCH] blkcg: correctly update stat

[Shaohua Li]

blkcg_bio_issue_check() checks throtl for stat update, which isn't good
because the bio could be splitted into small bios, the samll bios go
into blkcg_bio_issue_check again and we update stat for the small bios,
so we the stat is double charged. To fix this, we only update stat if
the bio doesn't have BIO_THROTTLED flag. The fix will update stat ahead
of bio skips from blk-throttle, but eventually the stat is correct.

This patch is on top of patch:
https://marc.info/?l=linux-block&m=151060860608914&w=2

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Shaohua Li <shli@fb.com>
---
 include/linux/blk-cgroup.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 58f3d25..6fbd9ea 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -690,7 +690,8 @@ static inline bool blkcg_bio_issue_check(struct request_queue *q,
 {
 	struct blkcg *blkcg;
 	struct blkcg_gq *blkg;
-	bool throtl = false;
+	bool throtl;
+	bool charged;
 
 	rcu_read_lock();
 	blkcg = bio_blkcg(bio);
@@ -707,9 +708,10 @@ static inline bool blkcg_bio_issue_check(struct request_queue *q,
 		spin_unlock_irq(q->queue_lock);
 	}
 
+	charged = bio_flagged(bio, BIO_THROTTLED);
 	throtl = blk_throtl_bio(q, blkg, bio);
 
-	if (!throtl) {
+	if (!charged) {
 		blkg = blkg ?: q->root_blkg;
 		blkg_rwstat_add(&blkg->stat_bytes, bio->bi_opf,
 				bio->bi_iter.bi_size);
-- 
2.9.5

Re: [PATCH] blkcg: correctly update stat

[Tejun Heo]

On Tue, Nov 14, 2017 at 10:05:07AM -0800, Shaohua Li wrote:
> blkcg_bio_issue_check() checks throtl for stat update, which isn't good
> because the bio could be splitted into small bios, the samll bios go
> into blkcg_bio_issue_check again and we update stat for the small bios,
> so we the stat is double charged. To fix this, we only update stat if
> the bio doesn't have BIO_THROTTLED flag. The fix will update stat ahead
> of bio skips from blk-throttle, but eventually the stat is correct.
> 
> This patch is on top of patch:
> https://marc.info/?l=linux-block&m=151060860608914&w=2
> 
> Cc: Tejun Heo <tj@kernel.org>
> Signed-off-by: Shaohua Li <shli@fb.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun