Re: [PATCH 2/3] make new alloc_pages_exact()

From: David Rientjes
Date: Thu Apr 14 2011 - 17:56:06 EST

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@xxxxxxxxxxxxxxxxxx>

Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
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