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

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Date:	Tue, 01 Apr 2014 14:01:02 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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, 2014-04-01 at 15:51 -0400, KOSAKI Motohiro wrote:
> >> So, I personally like 0 byte per default.
> >
> > If by this you mean 0 bytes == unlimited, then I agree. It's less harsh
> > then removing it entirely. So instead of removing the limit we can just
> > set it by default to 0, and in newseg() if shm_ctlmax == 0 then we don't
> > return EINVAL if the passed size is great (obviously), otherwise, if the
> > user _explicitly_ set it via sysctl then we respect that. Andrew, do you
> > agree with this? If so I'll send a patch.
> 
> Yes, my 0 bytes mean unlimited. I totally agree we shouldn't remove the knob
> entirely.

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?

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