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Date: Thu, 4 Oct 2012 18:50:08 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
To: Christoph Lameter <cl@linux.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
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Subject: Re: [PATCH 29/33] autonuma: page_autonuma
Reply-To: 
In-Reply-To: <0000013a2c223da2-632aa43e-21f8-4abd-a0ba-2e1b49881e3a-000000@email.amazonses.com>

Hi Christoph,

On Thu, Oct 04, 2012 at 02:16:14PM +0000, Christoph Lameter wrote:
> On Thu, 4 Oct 2012, Andrea Arcangeli wrote:
> 
> > Move the autonuma_last_nid from the "struct page" to a separate
> > page_autonuma data structure allocated in the memsection (with
> > sparsemem) or in the pgdat (with flatmem).
> 
> Note that there is a available word in struct page before the autonuma
> patches on x86_64 with CONFIG_HAVE_ALIGNED_STRUCT_PAGE.
> 
> In fact the page_autonuma fills up the structure to nicely fit in one 64
> byte cacheline.

Good point indeed.

So we could drop page_autonuma by creating a CONFIG_SLUB=y dependency
(AUTONUMA wouldn't be available in the kernel config if SLAB=y, and it
also wouldn't be available on 32bit archs but the latter isn't a
problem).

I think it's a reasonable alternative to page_autonuma. Certainly it
looks more appealing than taking over 16 precious bits from
page->flags. There are still pros and cons. I'm neutral on it so more
comments would be welcome ;).

Andrea

PS. randomly moved some in Cc over to Bcc as I overflowed the max
header allowed on linux-kernel oops!