linux-kernel - Re: [PATCH 01 of 66] disable lumpy when compaction is enabled

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Date:	Tue, 9 Nov 2010 22:30:49 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	linux-mm@...ck.org, Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>, Mike Travis <travis@....com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Chris Wright <chrisw@...s-sol.org>, bpicco@...hat.com,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Chris Mason <chris.mason@...cle.com>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 01 of 66] disable lumpy when compaction is enabled

On Tue, Nov 09, 2010 at 12:18:49PM +0900, KOSAKI Motohiro wrote:
> I'm talking very personal thing now. I'm usually testing both feature.
> Then, runtime switching makes my happy :-)
> However I don't know what are you and Mel talking and agree about this.
> So, If many developer prefer this approach, I don't oppose anymore.

Mel seem to still prefer I allow lumpy for hugetlbfs with a
__GFP_LUMPY specified only for hugetlbfs. But he measured compaction
is more reliable than lumpy at creating hugepages so he seems to be ok
with this too.

> But, I bet almost all distro choose CONFIG_COMPACTION=y. then, lumpy code
> will become nearly dead code. So, I like just kill than dead code. however
> it is also only my preference. ;)

Killing dead code is my preference too indeed. But then it's fine with
me to delete it only later. In short this is least intrusive
modification I could make to the VM that wouldn't than hang the system
when THP is selected because all pte young bits are ignored for >50%
of page reclaim invocations like lumpy requires.
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