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>,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <pzijlstr@redhat.com>, Ingo Molnar <mingo@elte.hu>,
Mel Gorman <mel@csn.ul.ie>, Hugh Dickins <hughd@google.com>,
Rik van Riel <riel@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Hillf Danton <dhillf@gmail.com>,
Andrew Jones <drjones@redhat.com>, Dan Smith <danms@us.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Paul Turner <pjt@google.com>,
Suresh Siddha <suresh.b.siddha@intel.com>,
Mike Galbraith <efault@gmx.de>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH 29/33] autonuma: page_autonuma
Date: Thu, 4 Oct 2012 20:38:19 +0200 [thread overview]
Message-ID: <20121004183819.GM25675@redhat.com> (raw)
In-Reply-To: <0000013a2cff3c3d-76e00716-2869-4dc8-8717-82f0136018d0-000000@email.amazonses.com>
Hi Christoph,
On Thu, Oct 04, 2012 at 06:17:37PM +0000, Christoph Lameter wrote:
> On Thu, 4 Oct 2012, Andrea Arcangeli wrote:
>
> > 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).
>
> Nope it should depend on page struct alignment. Other kernel subsystems
> may be depeding on page struct alignment in the future (and some other
> arches may already have that requirement)
But currently only SLUB x86 64bit selects
CONFIG_HAVE_ALIGNED_STRUCT_PAGE:
arch/Kconfig:config HAVE_ALIGNED_STRUCT_PAGE
arch/x86/Kconfig: select HAVE_ALIGNED_STRUCT_PAGE if SLUB && !M386
include/linux/mm_types.h: defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
include/linux/mm_types.h:#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE
mm/slub.c: defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
mm/slub.c: defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
mm/slub.c: defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
So in practice a dependency on CONFIG_HAVE_ALIGNED_STRUCT_PAGE would
still mean the same: only available when SLUB enables it, and only on
x86 64bit (ppc64?).
If you mean CONFIG_AUTONUMA=y should select (not depend) on
CONFIG_HAVE_ALIGNED_STRUCT_PAGE, that would allow to enable it in all
.configs but it would have a worse cons: losing 8bytes per page
unconditionally (even when booting on non-NUMA hardware).
The current page_autonuma solution is substantially memory-cheaper
than selecting CONFIG_HAVE_ALIGNED_STRUCT_PAGE: it allocates 2bytes
per page at boot time but only if booting on real NUMA hardware
(without altering the page structure). So to me it looks still quite a
decent tradeoff.
Thanks,
Andrea
next prev parent reply other threads:[~2012-10-04 18:39 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-04 16:50 Andrea Arcangeli
2012-10-04 18:17 ` your mail Christoph Lameter
2012-10-04 18:38 ` Andrea Arcangeli [this message]
2012-10-04 19:11 ` [PATCH 29/33] autonuma: page_autonuma Christoph Lameter
2012-10-05 11:11 ` Andrea Arcangeli
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