linux-kernel - Re: [PATCH 2/4] slqb: Record what node is local to a kmem_cache

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Date:	Thu, 1 Oct 2009 16:16:57 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Nick Piggin <npiggin@...e.de>, heiko.carstens@...ibm.com,
	sachinp@...ibm.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Tejun Heo <tj@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 2/4] slqb: Record what node is local to a kmem_cache_cpu

On Thu, Oct 01, 2009 at 11:03:16AM -0400, Christoph Lameter wrote:
> On Thu, 1 Oct 2009, Mel Gorman wrote:
> 
> > True, it might have been improved more if SLUB knew what local hugepage it
> > resided within as the kernel portion of the address space is backed by huge
> > TLB entries. Note that SLQB could have an advantage here early in boot as
> > the page allocator will tend to give it back pages within a single huge TLB
> > entry. It loses the advantage when the system has been running for a very long
> > time but it might be enough to skew benchmark results on cold-booted systems.
> 
> The page allocator serves pages aligned to huge page boundaries as far as
> I can remember.

You're right, it does, particularly early in boot. It loses the advantage
when the system has been running a long time and memory is mostly full but
the same will apply to SLQB.

> You can actually use huge pages in slub if you set the max
> order to 9. So a page obtained from the page allocator is always aligned
> properly.
> 

Fair point.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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