linux-kernel - Re: [PATCH 00/14][V5] Introduce io.latency io controller for cgroups

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Date:   Mon, 2 Jul 2018 15:41:48 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Josef Bacik <josef@...icpanda.com>
Cc:     kernel-team@...com, linux-block@...r.kernel.org,
        hannes@...xchg.org, tj@...nel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 00/14][V5] Introduce io.latency io controller for cgroups

On 7/2/18 3:26 PM, Andrew Morton wrote:
> On Fri, 29 Jun 2018 15:25:28 -0400 Josef Bacik <josef@...icpanda.com> wrote:
> 
>> This series adds a latency based io controller for cgroups.  It is based on the
>> same concept as the writeback throttling code, which is watching the overall
>> total latency of IO's in a given window and then adjusting the queue depth of
>> the group accordingly.  This is meant to be a workload protection controller, so
>> whoever has the lowest latency target gets the preferential treatment with no
>> thought to fairness or proportionality.  It is meant to be work conserving, so
>> as long as nobody is missing their latency targets the disk is fair game.
>>
>> We have been testing this in production for several months now to get the
>> behavior right and we are finally at the point that it is working well in all of
>> our test cases.  With this patch we protect our main workload (the web server)
>> and isolate out the system services (chef/yum/etc).  This works well in the
>> normal case, smoothing out weird request per second (RPS) dips that we would see
>> when one of the system services would run and compete for IO resources.  This
>> also works incredibly well in the runaway task case.
>>
>> The runaway task usecase is where we have some task that slowly eats up all of
>> the memory on the system (think a memory leak).  Previously this sort of
>> workload would push the box into a swapping/oom death spiral that was only
>> recovered by rebooting the box.  With this patchset and proper configuration of
>> the memory.low and io.latency controllers we're able to survive this test with a
>> at most 20% dip in RPS.
> 
> Is this purely useful for spinning disks, or is there some
> applicability to SSDs and perhaps other storage devices?  Some
> discussion on this topic would be useful.
> 
> Patches 5, 7 & 14 look fine to me - go wild.  #14 could do with a
> couple of why-we're-doing-this comments, but I say that about
> everything ;)

I want to queue this up for 4.19 shortly - is the above an acked-by? Andrewed-by?
Which do you prefer? :-)

-- 
Jens Axboe