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

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Date:	Sun, 13 Apr 2014 16:15:40 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	Manfred Spraul <manfred@...orfullife.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.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 Sun, 2014-04-13 at 20:05 +0200, Manfred Spraul wrote:
> Hi Andrew,
> 
> On 04/02/2014 12:08 AM, Andrew Morton wrote:
> > Well, I'm assuming 64GB==infinity. It *was* infinity in the RHEL5 
> > timeframe, but infinity has since become larger so pickanumber. 
> 
> I think infinity is the right solution:
> The only common case where infinity is wrong would be Android - and 
> Android disables sysv shm entirely.
> 
> There are two patches:
> http://marc.info/?l=linux-kernel&m=139730332306185&q=raw

If you apply this one, please include the below, which updates a missing
definition for SHMALL.

diff --git a/include/uapi/linux/shm.h b/include/uapi/linux/shm.h
index d9497b7..0774ec4 100644
--- a/include/uapi/linux/shm.h
+++ b/include/uapi/linux/shm.h
@@ -9,14 +9,14 @@
 
 /*
  * SHMMAX, SHMMNI and SHMALL are upper limits are defaults which can
- * be increased by sysctl
+ * be decreased by sysctl.
  */
 
 #define SHMMAX ULONG_MAX		 /* max shared seg size (bytes) */
 #define SHMMIN 1			 /* min shared seg size (bytes) */
 #define SHMMNI 4096			 /* max num of segs system wide */
 #ifndef __KERNEL__
-#define SHMALL (SHMMAX/getpagesize()*(SHMMNI/16))
+#define SHMALL ULONG_MAX
 #endif
 #define SHMSEG SHMMNI			 /* max shared segs per process */
 


> http://marc.info/?l=linux-kernel&m=139727299800644&q=raw
> 
> Could you apply one of them?
> I wrote the first one, thus I'm biased which one is better.
> 
> --
>      Manfred


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