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

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Date:	Thu, 28 Apr 2011 09:02:57 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Timur Tabi <timur@...escale.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()

On Wed, 2011-04-27 at 16:42 -0500, Timur Tabi wrote:
> 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.

I did actually go add a bunch of printks to it at one point.  It did
seem to be working just fine and freeing the right amount of memory.

-- Dave

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