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Subject: Re: [PATCHSET v2 block/for-5.8] iocost: improve use_delay and latency
 target handling
To:     Tejun Heo <tj@kernel.org>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com, cgroups@vger.kernel.org, newella@fb.com,
        josef@toxicpanda.com, asml.silence@gmail.com, ming.lei@redhat.com,
        bvanassche@acm.org
References: <20200413162758.97252-1-tj@kernel.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <6ee6360e-1a35-874c-2263-6fb21da66591@kernel.dk>
Date:   Thu, 30 Apr 2020 15:55:30 -0600
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On 4/13/20 10:27 AM, Tejun Heo wrote:
> Changes from v1[1]
> 
> * Dropped 0002-block-add-request-io_data_len.patch and updated to use
>   rq->stats_sectors instead as suggested by Pavel Begunkov.
> 
> This patchset improves the following two iocost control behaviors.
> 
> * iocost was failing to punish heavy shared IO generators (file metadata, memory
>   reclaim) through use_delay mechanism - use_delay automatically decays which
>   works well for iolatency but doesn't match how iocost behaves. This led to
>   e.g. memory bombs which generate a lot of swap IOs to use over their allotted
>   amount. This is fixed by adding non-decaying use_delay mechanism.
> 
> * The same latency targets were being applied regardless of the IO sizes. While
>   this works fine for loose targets, it gets in the way when trying to tigthen
>   them - a latency target adequate for a 4k IO is too short for a 1 meg IO.
>   iocost now discounts the size portion of cost when testing whether a given IO
>   met or missed its latency target.
> 
> While at it, it also makes minor changse to iocost_monitor.py.
> 
> This patchset contains the following five patches.
> 
>  0001-blk-iocost-switch-to-fixed-non-auto-decaying-use_del.patch
>  0002-blk-iocost-account-for-IO-size-when-testing-latencie.patch
>  0003-iocost_monitor-exit-successfully-if-interval-is-zero.patch
>  0004-iocost_monitor-drop-string-wrap-around-numbers-when-.patch
> 
> and is also available in the following git branch.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git iocost-delay-latency-v2
> 
> diffstat follows. Thanks.
> 
>  block/Kconfig                  |    1 
>  block/blk-cgroup.c             |    6 ++++
>  block/blk-iocost.c             |   56 +++++++++++++++++++++++++++++------------
>  include/linux/blk-cgroup.h     |   43 ++++++++++++++++++++++++-------
>  tools/cgroup/iocost_monitor.py |   48 +++++++++++++++++++----------------
>  5 files changed, 106 insertions(+), 48 deletions(-)

Applied, thanks Tejun.

-- 
Jens Axboe