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

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Date:	Tue, 1 Apr 2014 18:49:21 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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, Apr 1, 2014 at 5:48 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> 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?

64GB is infinity at that time, but it no longer near infinity today. I like
very large or total memory proportional number.

But I'm open. Please let me see if anyone know the disadvantage of
very large value.
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