From: Tejun Heo tj@kernel.org
mainline inclusion from mainline-5.4-rc1 commit e1518f63f246831af222758ead022cd40e79fab8 category: feature bugzilla: 38688 CVE: NA
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Merges have the same problem that forced-bios had which is fixed by the previous patch. The cost of a merge is calculated at the time of issue and force-advances vtime into the future. Until global vtime catches up, how the cgroup's hweight changes in the meantime doesn't matter and it often leads to situations where the cost is calculated at one hweight and paid at a very different one. See the previous patch for more details.
Fix it by never advancing vtime into the future for merges. If budget is available, vtime is advanced. Otherwise, the cost is charged as debt.
This brings merge cost handling in line with issue cost handling in ioc_rqos_throttle().
Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Hou Tao houtao1@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- block/blk-iocost.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-)
diff --git a/block/blk-iocost.c b/block/blk-iocost.c index 88056825adcf5..d45fc13004739 100644 --- a/block/blk-iocost.c +++ b/block/blk-iocost.c @@ -1785,28 +1785,39 @@ static void ioc_rqos_merge(struct rq_qos *rqos, struct request *rq, struct bio *bio) { struct ioc_gq *iocg = blkg_to_iocg(bio->bi_blkg); + struct ioc *ioc = iocg->ioc; sector_t bio_end = bio_end_sector(bio); + struct ioc_now now; u32 hw_inuse; u64 abs_cost, cost;
- /* add iff the existing request has cost assigned */ - if (!rq->bio || !rq->bio->bi_iocost_cost) + /* bypass if disabled or for root cgroup */ + if (!ioc->enabled || !iocg->level) return;
abs_cost = calc_vtime_cost(bio, iocg, true); if (!abs_cost) return;
+ ioc_now(ioc, &now); + current_hweight(iocg, NULL, &hw_inuse); + cost = abs_cost_to_cost(abs_cost, hw_inuse); + /* update cursor if backmerging into the request at the cursor */ if (blk_rq_pos(rq) < bio_end && blk_rq_pos(rq) + blk_rq_sectors(rq) == iocg->cursor) iocg->cursor = bio_end;
- current_hweight(iocg, NULL, &hw_inuse); - cost = div64_u64(abs_cost * HWEIGHT_WHOLE, hw_inuse); - bio->bi_iocost_cost = cost; - - atomic64_add(cost, &iocg->vtime); + /* + * Charge if there's enough vtime budget and the existing request + * has cost assigned. Otherwise, account it as debt. See debt + * handling in ioc_rqos_throttle() for details. + */ + if (rq->bio && rq->bio->bi_iocost_cost && + time_before_eq64(atomic64_read(&iocg->vtime) + cost, now.vnow)) + iocg_commit_bio(iocg, bio, cost); + else + atomic64_add(abs_cost, &iocg->abs_vdebt); }
static void ioc_rqos_done_bio(struct rq_qos *rqos, struct bio *bio)