linux-kernel - Re: [PATCH 55 of 66] select CONFIG_COMPACTION if TRANSPARENT

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Message-Id: <20101109151756.BC7B.A69D9226@jp.fujitsu.com>
Date:	Tue,  9 Nov 2010 15:20:33 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com, 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 55 of 66] select CONFIG_COMPACTION if TRANSPARENT_HUGEPAGE enabled

> From: Andrea Arcangeli <aarcange@...hat.com>
> 
> With transparent hugepage support we need compaction for the "defrag" sysfs
> controls to be effective.
> 
> Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
> ---
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -305,6 +305,7 @@ config NOMMU_INITIAL_TRIM_EXCESS
>  config TRANSPARENT_HUGEPAGE
>  	bool "Transparent Hugepage Support"
>  	depends on X86 && MMU
> +	select COMPACTION
>  	help
>  	  Transparent Hugepages allows the kernel to use huge pages and
>  	  huge tlb transparently to the applications whenever possible.

I dislike this. THP and compaction are completely orthogonal. I think 
you are talking only your performance recommendation. I mean I dislike
Kconfig 'select' hell and I hope every developers try to avoid it as 
far as possible.

Thanks.



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