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

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Date:	Tue, 1 Apr 2014 14:48:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Davidlohr Bueso <davidlohr@...com>,
	Manfred Spraul <manfred@...orfullife.com>, aswin@...com,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] ipc,shm: increase default size for shmmax

On Tue, 1 Apr 2014 17:41:54 -0400 KOSAKI Motohiro <kosaki.motohiro@...il.com> 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?

Then we can blame RH if something goes wrong ;)
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