linux-kernel - Re: [PATCH 00/25] Cleanup and optimise the page allocator V5

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Date:	Fri, 20 Mar 2009 12:04:42 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
cc:	Linux Memory Management List <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 00/25] Cleanup and optimise the page allocator V5

On Fri, 20 Mar 2009, Mel Gorman wrote:

> hmm, I'm missing something in your reasoning. The contention I saw for
> zone->lru_lock
>
> &zone->lru_lock          37350 [<ffffffff8029d6fe>] ____pagevec_lru_add+0x9c/0x172
> &zone->lru_lock          55423 [<ffffffff8029d377>] release_pages+0x10a/0x21b
> &zone->lru_lock            402 [<ffffffff8029d9d9>] activate_page+0x4f/0x147
> &zone->lru_lock              6 [<ffffffff8029dbbd>] put_page+0x94/0x122
>
> So I just assumed it was LRU pages being taken off and freed that was
> causing the contention. Can SLUB affect that?

No. But it can affect the taking of the zone lock.

> Maybe you meant zone->lock and SLUB could tune buffers more to avoid
> that if that lock was hot. That is one alternative but the later patches
> proposed an alternative whereby high-order and compound pages could be
> stored on the PCP lists. Compound only really helps SLUB but high-order
> also helped stacks, signal handlers and the like so it seemed like a
> good idea one way or the other. Course, this meant a search of the PCP
> lists or increasing the size of the PCP structure - swings and
> roundabouts :/

Maybe include those as well? Its good stuff.
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