linux-kernel - Re: [PATCH] ipc,shm: disable shmmax and shmall by default

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Date:	Sun, 06 Apr 2014 08:42:02 +0200
From:	Manfred Spraul <manfred@...orfullife.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Davidlohr Bueso <davidlohr@...com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, aswin@...com,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Greg Thelen <gthelen@...gle.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] ipc,shm: disable shmmax and shmall by default

Hi,

On 04/05/2014 08:24 PM, KOSAKI Motohiro wrote:
> On Fri, Apr 4, 2014 at 1:00 AM, Davidlohr Bueso <davidlohr@...com> wrote:
>> I don't think it makes much sense to set unlimited for both 0 and
>> ULONG_MAX, that would probably just create even more confusion.
I agree.
Unlimited was INT_MAX since 0.99.10 and ULONG_MAX since 2.3.39 (with 
proper backward compatibility for user space).

Adding a second value for unlimited just creates confusion.
>> But then again, we shouldn't even care about breaking things with shmmax
>> or shmall with 0 value, it just makes no sense from a user PoV. shmmax
>> cannot be 0 unless there's an overflow, which voids any valid cases, and
>> thus shmall cannot be 0 either as it would go against any values set for
>> shmmax. I think it's safe to ignore this.
> Agreed.
> IMHO, until you find out any incompatibility issue of this, we don't
> need the switch
> because we can't make good workaround for that. I'd suggest to merge your patch
> and see what happen.
I disagree:
- "shmctl(,IPC_INFO,&buf); if (my_memory_size > buf.shmmax) 
perror("change shmmax");" worked correctly since 0.99.10. I don't think 
that merging the patch and seeing what happens is the right approach.
- setting shmmax by default to ULONG_MAX is the perfect workaround.

What reasons are there against the one-line patch?
 >
 > -#define SHMMAX 0x2000000                /* max shared seg size 
(bytes) */
 > +#define SHMMAX ULONG_MAX                /* max shared seg size 
(bytes) */
 >

--
     Manfred
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