Subject: Re: [PATCH 2/3] make new alloc_pages_exact()
From: Dave Hansen <dave@linux.vnet.ibm.com>
To: Timur Tabi <timur@freescale.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andi Kleen <andi@firstfloor.org>, Mel Gorman <mel@csn.ul.ie>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Nazarewicz <mina86@mina86.com>,
        David Rientjes <rientjes@google.com>
In-Reply-To: <4DB88DAF.2010504@freescale.com>
References: <20110414200139.ABD98551@kernel>
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	 <1303940249.9516.366.camel@nimitz>  <4DB88DAF.2010504@freescale.com>
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Date: Thu, 28 Apr 2011 09:02:57 -0700
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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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