linux-kernel - Re: [PATCH] mm, numa: Do not group on RO pages

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Date:	Fri, 2 Aug 2013 21:56:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Don Morris <don.morris@...com>
Cc:	Mel Gorman <mgorman@...e.de>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, riel@...hat.com
Subject: Re: [PATCH] mm, numa: Do not group on RO pages

> +	/*
> +	 * Avoid grouping on DSO/COW pages in specific and RO pages
> +	 * in general, RO pages shouldn't hurt as much anyway since
> +	 * they can be in shared cache state.
> +	 */

OK, so that comment is crap. Its that you cannot work into RO pages and
this RO pages don't establish a collaboration.

> +	if (page_mapcount(page) != 1 && !pmd_write(pmd))
> +		flags |= TNF_NO_GROUP;

Rik also noted that mapcount == 1 will trivially not form groups. This
should indeed be so but I didn't test it without that clause.
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