linux-kernel - Re: [PATCH 3/6] mm: CONFIG_MMU for PG

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Date:	Wed, 11 Nov 2009 10:48:07 +0000 (GMT)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Izik Eidus <ieidus@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Andi Kleen <andi@...stfloor.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 3/6] mm: CONFIG_MMU for PG_mlocked

On Wed, 11 Nov 2009, KOSAKI Motohiro wrote:
> > Remove three degrees of obfuscation, left over from when we had
> > CONFIG_UNEVICTABLE_LRU.  MLOCK_PAGES is CONFIG_HAVE_MLOCKED_PAGE_BIT
> > is CONFIG_HAVE_MLOCK is CONFIG_MMU.  rmap.o (and memory-failure.o)
> > are only built when CONFIG_MMU, so don't need such conditions at all.
> 
> I don't recall why Lee added this config option. but it seems very
> reasonable and I storongly like it.
> 
> At least, vmscan folks never said "please try to disable CONFIG_MLOCK".
> It mean this option didn't help our debug.
> 
> 	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>

Thanks.  CONFIG_HAVE_MLOCKED_PAGE_BIT and CONFIG_HAVE_MLOCK were both
just internal, automatically defaulted options which the user never
saw (except in .config).  I think they were there to sort out the
interdependencies between CONFIG_MMU and CONFIG_UNEVICTABLE_LRU,
and probably other historical issues while people decided whether
or not to go ahead with having a page bit for the thing.  So no
user should notice their disappearance: removing them just makes
the code clearer, that's all.

Hugh
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