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Date:   Mon, 2 Jul 2018 14:47:57 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Josef Bacik <josef@toxicpanda.com>, kernel-team@fb.com,
        linux-block@vger.kernel.org, hannes@cmpxchg.org, tj@kernel.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 00/14][V5] Introduce io.latency io controller for
 cgroups
Message-Id: <20180702144757.0138984124f97bf0b8f8de31@linux-foundation.org>
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        <20180702142639.752759da566fd9074cf8edfe@linux-foundation.org>
        <08f3bef3-7189-a368-74d9-b4c5e0edc824@kernel.dk>
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On Mon, 2 Jul 2018 15:41:48 -0600 Jens Axboe <axboe@kernel.dk> wrote:

> On 7/2/18 3:26 PM, Andrew Morton wrote:
> > On Fri, 29 Jun 2018 15:25:28 -0400 Josef Bacik <josef@toxicpanda.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? :-)

Quacked-at-by: Andrew

Hannes's acks are good.  Feel free to add mine as well ;)