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

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Date:	Thu, 14 Apr 2011 14:55:50 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Timur Tabi <timur@...escale.com>,
	Andi Kleen <andi@...stfloor.org>, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Nazarewicz <mina86@...a86.com>
Subject: Re: [PATCH 2/3] make new alloc_pages_exact()

On Thu, 14 Apr 2011, Dave Hansen wrote:

> 
> What I really wanted in the end was a highmem-capable
> alloc_pages_exact(), so here it is.  This function can be used to
> allocate unmapped (like highmem) non-power-of-two-sized areas of
> memory.  This is in constast to get_free_pages_exact() which can only
> allocate from lowmem.
> 
> My plan is to use this in the virtio_balloon driver to allocate large,
> oddly-sized contiguous areas.
> 
> The new __alloc_pages_exact() now takes a size in numbers of pages,
> and returns a 'struct page', which means it can now address
> highmem.  The (new) argument order mirrors alloc_pages() itself.
> 
> It's a bit unfortunate that this introduces __free_pages_exact()
> alongside free_pages_exact().  But that mess already exists with
> __free_pages() vs. free_pages_exact().  So, at worst, this mirrors the
> mess that we already have.
> 
> I'm also a bit worried that I've not put in something named
> alloc_pages_exact(), but that behaves differently than it did before
> this set.  I got all of the in-tree cases, but I'm a bit worried about
> stragglers elsewhere.  So, I'm calling this __alloc_pages_exact() for
> the moment.  We can take out the __ some day if it bothers people.
> 
> Note that the __get_free_pages() has a !GFP_HIGHMEM check.  Now that
> we are using alloc_pages_exact() instead of __get_free_pages() for
> get_free_pages_exact(), we had to add a new check in
> get_free_pages_exact().
> 
> This has been compile and boot tested, and I checked that
> 
> 	echo 2 > /sys/kernel/profiling
> 
> still works, since it uses get_free_pages_exact().
> 
> Signed-off-by: Dave Hansen <dave@...ux.vnet.ibm.com>

Acked-by: David Rientjes <rientjes@...gle.com>
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