linux-kernel - Re: [PATCH BUGFIX/IMPROVEMENT V2 0/3] three bfq fixes restoring service guarantees with random sync writes in bg

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Date:   Thu, 31 Aug 2017 19:31:51 +0200
From:   Mike Galbraith <efault@....de>
To:     Paolo Valente <paolo.valente@...aro.org>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>, broonie@...nel.org,
        lee.tibbert@...il.com, oleksandr@...alenko.name
Subject: Re: [PATCH BUGFIX/IMPROVEMENT V2 0/3] three bfq fixes restoring
 service guarantees with random sync writes in bg

On Thu, 2017-08-31 at 19:12 +0200, Paolo Valente wrote:
> > Il giorno 31 ago 2017, alle ore 19:06, Mike Galbraith <efault@....de> ha scritto:
> > 
> > On Thu, 2017-08-31 at 15:42 +0100, Mel Gorman wrote:
> >> On Thu, Aug 31, 2017 at 08:46:28AM +0200, Paolo Valente wrote:
> >>> [SECOND TAKE, with just the name of one of the tester fixed]
> >>> 
> >>> Hi,
> >>> while testing the read-write unfairness issues reported by Mel, I
> >>> found BFQ failing to guarantee good responsiveness against heavy
> >>> random sync writes in the background, i.e., multiple writers doing
> >>> random writes and systematic fdatasync [1]. The failure was caused by
> >>> three related bugs, because of which BFQ failed to guarantee to
> >>> high-weight processes the expected fraction of the throughput.
> >>> 
> >> 
> >> Queued on top of Ming's most recent series even though that's still a work
> >> in progress. I should know in a few days how things stand.
> > 
> > It seems to have cured an interactivity issue I regularly meet during
> > kbuild final link/depmod phase of fat kernel kbuild, especially bad
> > with evolution mail usage during that on spinning rust.  Can't really
> > say for sure given this is not based on measurement.
> >
> 
> 
> Great!  Actually, when I found these bugs, I thought also about the
> issues you told me you experienced with updatedb running.  But then I
> forgot to tell you that these fixes might help.

I'm going to actively test that, because that is every bit as
infuriating as the evolution thing, only updatedb is nukable.  In fact,
it infuriated me to the point that it no longer has a crontab entry,
runs only when I decide to run it.  At this point, I'll be pretty
surprised if that rotten <naughty words> is still alive.

	-Mike