blk-iocost: switch to fixed non-auto-decaying use_delay
The use_delay mechanism was introduced by blk-iolatency to hold memory allocators accountable for the reclaim and other shared IOs they cause. The duration of the delay is dynamically balanced between iolatency increasing the value on each target miss and it auto-decaying as time passes and threads get delayed on it. While this works well for iolatency, iocost's control model isn't compatible with it. There is no repeated "violation" events which can be balanced against auto-decaying. iocost instead knows how much a given cgroup is over budget and wants to prevent that cgroup from issuing IOs while over budget. Until now, iocost has been adding the cost of force-issued IOs. However, this doesn't reflect the amount which is already over budget and is simply not enough to counter the auto-decaying allowing anon-memory leaking low priority cgroup to go over its alloted share of IOs. As auto-decaying doesn't make much sense for iocost, this patch introduces a different mode of operation for use_delay - when blkcg_set_delay() are used insted of blkcg_add/use_delay(), the delay duration is not auto-decayed until it is explicitly cleared with blkcg_clear_delay(). iocost is updated to keep the delay duration synchronized to the budget overage amount. With this change, iocost can effectively police cgroups which generate significant amount of force-issued IOs. Signed-off-by:Tejun Heo <tj@kernel.org> Cc: Josef Bacik <josef@toxicpanda.com> Signed-off-by:
Jens Axboe <axboe@kernel.dk>
parent
accea322
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