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

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Message-ID: <CAHGf_=rhXrBQSmDBJJ-vPxBbhjJ91Fh2iWe1cf_UQd-tCfpb2w@mail.gmail.com>
Date:	Tue, 1 Apr 2014 17:12:50 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Davidlohr Bueso <davidlohr@...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, Apr 1, 2014 at 5:01 PM, Davidlohr Bueso <davidlohr@...com> wrote:
> 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?

I don't think people use 0 for disabling. but ULONG_MAX make sense to me too.
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