path: root/block/blk-throttle.c
diff options
authorShaohua Li <>2017-12-20 11:10:17 -0700
committerJens Axboe <>2017-12-20 11:10:17 -0700
commit111be883981748acc9a56e855c8336404a8e787c (patch)
treefe3766fcad8f4996f049d2562ad0d62b7bb8fc98 /block/blk-throttle.c
parent0abc2a10389f0c9070f76ca906c7382788036b93 (diff)
block-throttle: avoid double charge
If a bio is throttled and split after throttling, the bio could be resubmited and enters the throttling again. This will cause part of the bio to be charged multiple times. If the cgroup has an IO limit, the double charge will significantly harm the performance. The bio split becomes quite common after arbitrary bio size change. To fix this, we always set the BIO_THROTTLED flag if a bio is throttled. If the bio is cloned/split, we copy the flag to new bio too to avoid a double charge. However, cloned bio could be directed to a new disk, keeping the flag be a problem. The observation is we always set new disk for the bio in this case, so we can clear the flag in bio_set_dev(). This issue exists for a long time, arbitrary bio size change just makes it worse, so this should go into stable at least since v4.2. V1-> V2: Not add extra field in bio based on discussion with Tejun Cc: Vivek Goyal <> Cc: Acked-by: Tejun Heo <> Signed-off-by: Shaohua Li <> Signed-off-by: Jens Axboe <>
Diffstat (limited to 'block/blk-throttle.c')
1 files changed, 1 insertions, 7 deletions
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 825bc29..d19f416 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -2226,13 +2226,7 @@ again:
- /*
- * As multiple blk-throtls may stack in the same issue path, we
- * don't want bios to leave with the flag set. Clear the flag if
- * being issued.
- */
- if (!throttled)
- bio_clear_flag(bio, BIO_THROTTLED);
+ bio_set_flag(bio, BIO_THROTTLED);
if (throttled || !td->track_bio_latency)