linux-kernel - Re: [PATCH 2/3] make new alloc_pages

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Message-ID: <4DB88DAF.2010504@freescale.com>
Date:	Wed, 27 Apr 2011 16:42:07 -0500
From:	Timur Tabi <timur@...escale.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
CC:	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH 2/3] make new alloc_pages_exact()

Dave Hansen wrote:
>> Is there an easy way to verify that alloc_pages_exact(5MB) really does allocate
>> > only 5MB and not 8MB?

> I'm not sure why you're asking.  How do we know that the _normal_
> allocator only gives us 4k when we ask for 4k?  Well, that's just how it
> works.  If alloc_pages_exact() returns success, you know it's got the
> amount of memory that you asked for, and only that plus a bit of masking
> for page alignment.
> 
> Have you seen alloc_pages_exact() behaving in some other way?

I've never tested this part of alloc_pages_exact(), even when I wrote (the first
version of) it.  I just took it on faith that it actually did what it was
supposed to do.

-- 
Timur Tabi
Linux kernel developer at Freescale

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