linux-kernel - Re: [PATCH 4/8] mm: FOLL_DUMP replace FOLL

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Message-ID: <4AA6A989.60907@redhat.com>
Date:	Tue, 08 Sep 2009 14:59:21 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	Jeff Chua <jeff.chua.linux@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 4/8] mm: FOLL_DUMP replace FOLL_ANON

Hugh Dickins wrote:
> The "FOLL_ANON optimization" and its use_zero_page() test have caused
> confusion and bugs: why does it test VM_SHARED? for the very good but
> unsatisfying reason that VMware crashed without.  As we look to maybe
> reinstating anonymous use of the ZERO_PAGE, we need to sort this out.
> 
> Easily done: it's silly for __get_user_pages() and follow_page() to
> be guessing whether it's safe to assume that they're being used for
> a coredump (which can take a shortcut snapshot where other uses must
> handle a fault) - just tell them with GUP_FLAGS_DUMP and FOLL_DUMP.
> 
> get_dump_page() doesn't even want a ZERO_PAGE: an error suits fine.
> 
> Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>

Acked-by: Rik van Riel <riel@...hat.com>

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