linux-kernel - Re: [PATCH] Reduce vm_stat cacheline contention in __vm_enough

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Message-ID: <m2hb3c287e.fsf@firstfloor.org>
Date:	Thu, 13 Oct 2011 08:59:49 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Christoph Lameter <cl@...two.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dimitri Sivanich <sivanich@....com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] Reduce vm_stat cacheline contention in __vm_enough_memory

Mel Gorman <mel@....ul.ie> writes:
>
> If vm_enough_memory is being heavily hit as well, it implies that this
> workload is mmap-intensive which is pretty inefficient in itself. I

Saw it with tmpfs originally. No need to be mmap intensive. Just
do lots of IOs on tmpfs.

> guess it would also apply to workloads that are malloc-intensive for
> large buffers but I'd expect the cache line bounces to only dominate if
> there was little or no computation on the resulting buffers.

I think you severly underestimate the costs of bouncing cache lines
on >2S.

> As a result, I wonder how realistic is this test workload and who useful
> fixing this problem is in general?

It's kind of bad if tmpfs doesn't scale.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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