linux-kernel - Re: [PATCH] vmscan: skip freeing memory from zones with lots free

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Message-ID: <20081210050938.GF8434@wotan.suse.de>
Date:	Wed, 10 Dec 2008 06:09:38 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Rik van Riel <riel@...hat.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH] vmscan: skip freeing memory from zones with lots free

On Mon, Dec 08, 2008 at 03:25:10PM -0500, Rik van Riel wrote:
> KOSAKI Motohiro wrote:
> 
> >+	for (o = order; o < MAX_ORDER; o++) {
> >+		if (z->free_area[o].nr_free)
> >+			return 1;
> 
> Since page breakup and coalescing always manipulates .nr_free,
> I wonder if it would make sense to pack the nr_free variables
> in their own cache line(s), so we have fewer cache misses when
> going through zone_watermark_ok() ?

For order-0 allocations, they should not be touched at all. For
higher order allocations in performance critical paths, we should
try to fix those to use order-0 ;)

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