linux-kernel - Re: [PATCH 7/8] mm: reinstate ZERO

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Message-ID: <Pine.LNX.4.64.0909152111330.22199@sister.anvils>
Date:	Tue, 15 Sep 2009 21:15:07 +0100 (BST)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 7/8] mm: reinstate ZERO_PAGE

On Wed, 9 Sep 2009, KAMEZAWA Hiroyuki wrote:
> On Tue, 8 Sep 2009 12:56:57 +0100 (BST)
> Hugh Dickins <hugh.dickins@...cali.co.uk> wrote:
> > 
> > Though I like that we don't _need_ to change mlock.c for reinstated
> > ZERO_PAGE, this morning I'm having trouble persuading myself that
> > mlocking a readonly anonymous area is too silly to optimize for.
> > 
> > Maybe the very people who persuaded you to bring back the anonymous
> > use of ZERO_PAGE, are also doing a huge mlock of the area first?
> No, as far as I know, they'll not do huge mlock.

Thanks for that (not entirely conclusive!) info.

I've decided for the moment to make a couple of further optimizations
in mlock.c (along with the comment you asked for), and leave adding
another __get_user_pages flag until a case for it is demonstrated.

Small patch series following shortly.

Hugh
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