Re: [PATCH] ipc,shm: increase default size for shmmax

From: Davidlohr Bueso
Date: Tue Apr 01 2014 - 18:02:49 EST


On Tue, 2014-04-01 at 14:48 -0700, Andrew Morton wrote:
> On Tue, 1 Apr 2014 17:41:54 -0400 KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx> wrote:
>
> > >> > Hmmm so 0 won't really work because it could be weirdly used to disable
> > >> > shm altogether... we cannot go to some negative value either since we're
> > >> > dealing with unsigned, and cutting the range in half could also hurt
> > >> > users that set the limit above that. So I was thinking of simply setting
> > >> > SHMMAX to ULONG_MAX and be done with it. Users can then set it manually
> > >> > if they want a smaller value.
> > >> >
> > >> > Makes sense?
> > >>
> > >> I don't think people use 0 for disabling. but ULONG_MAX make sense to me too.
> > >
> > > Distros could have set it to [U]LONG_MAX in initscripts ten years ago
> > > - less phone calls, happier customers. And they could do so today.
> > >
> > > But they haven't. What are the risks of doing this?
> >
> > I have no idea really. But at least I'm sure current default is much worse.
> >
> > 1. Solaris changed the default to total-memory/4 since Solaris 10 for DB.
> > http://www.postgresql.org/docs/9.1/static/kernel-resources.html
> >
> > 2. RHEL changed the default to very big size since RHEL5 (now it is
> > 64GB). Even tough many box don't have 64GB memory at that time.
>
> Ah-hah, that's interesting info.
>
> Let's make the default 64GB?

But again, yet another arbitrary value...

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