[dm-devel] [PATCH 3/7] dm: add reserved_bio_based_ios module parameter
Frank Mayhar
fmayhar at google.com
Wed Sep 18 15:17:01 UTC 2013
On Thu, 2013-09-12 at 19:17 -0400, Mikulas Patocka wrote:
>
> On Thu, 12 Sep 2013, Mike Snitzer wrote:
>
> > On Thu, Sep 12 2013 at 6:47pm -0400,
> > Mikulas Patocka <mpatocka at redhat.com> wrote:
> >
> > > We don't need this. bio-based i/o should be fine with a small mempool,
> > > there is no need to make it tunable.
> >
> > I'd like to get Frank's insight here. He clearly had an interest in
> > tuning bio-based also. While 16 shouldn't really hurt it could still be
> > artifically high. I'm not opposed to exposing a sane default but
> > allowing other to experiemnt (in production workloads) with smaller
> > values that still enable forward progress should memory get exhausted.
> >
> > Mike
>
> I would do it this way: if Frank gets a measurable improvement in memory
> consumption when the values is dropped from 16 to a lower number (4 or
> maybe 1), then I would drop the value by default (don't make it tunable,
> drop it for all users).
>
> If there is no improvement when the value is lowered, I'd leave it as it
> is, on 16.
I haven't had time to look at this lately, but I did see a small but
measurable reduction in memory consumption when I was dealing with this
before. The real problem for us is the fact that we'll have tons of
these devices so even a small memory reduction means a lot when
multiplied by, say, a hundred devices across a thousand machines. And
that's a _small_ number.
That said, I wouldn't want to see all Linux installs limited by our
specific case, which is why I would vote for a tunable rather than a
fixed, hardcoded value.
--
Frank Mayhar
310-460-4042
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