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Re: LTP testing (shmat01)

To: Ralf Baechle <ralf@oss.sgi.com>
Subject: Re: LTP testing (shmat01)
From: Carsten Langgaard <carstenl@mips.com>
Date: Fri, 05 Jul 2002 08:30:48 +0200
Cc: linux-mips@oss.sgi.com
References: <3D246924.542682B2@mips.com> <20020704193414.A29570@dea.linux-mips.net> <3D249181.D9147AAE@mips.com> <20020704215614.B29422@dea.linux-mips.net>
Sender: owner-linux-mips@oss.sgi.com
Ralf Baechle wrote:

> On Thu, Jul 04, 2002 at 08:18:41PM +0200, Carsten Langgaard wrote:
>
> > > any power of 2 > PAGE_SIZE.
> >
> > Ok, I see, but is there any reason for us to be different than the
> > rest of the world ?
>
> Imho the your question already wrong :-)  Any assumption about the
> constant's value in a piece of code is wrong.
>
> The reason why the constant's value was choosen are virtually indexed
> caches.  The value allows attaching of shared memory segment without
> any cache flushes.
>
> Other architectures also use different values from PAGE_SIZE like IA64 1MB,
> SH 16kB and Sparc not even a constant value accross all architectures
> variants, so unlike what your posting implicates we're not that unusual.

Using PAGE_SIZE is ok, even though it may differ from different architecture,
because SHMLBA is defined as the following in /usr/include/sys/shm.h:
#define SHMLBA          (__getpagesize ())

So I would expect the user application and the kernel should have the same
idea of what the size is.

>   Ralf

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