linux-kernel - Re: [PATCH 1/8] mm: munlock use follow

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Date:	Fri, 11 Sep 2009 20:07:13 +0900
From:	Hiroaki Wakabayashi <primulaelatior@...il.com>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	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 1/8] mm: munlock use follow_page

2009/9/8 Hugh Dickins <hugh.dickins@...cali.co.uk>:
> Hiroaki Wakabayashi points out that when mlock() has been interrupted
> by SIGKILL, the subsequent munlock() takes unnecessarily long because
> its use of __get_user_pages() insists on faulting in all the pages
> which mlock() never reached.
>
> It's worse than slowness if mlock() is terminated by Out Of Memory kill:
> the munlock_vma_pages_all() in exit_mmap() insists on faulting in all the
> pages which mlock() could not find memory for; so innocent bystanders are
> killed too, and perhaps the system hangs.
>
> __get_user_pages() does a lot that's silly for munlock(): so remove the
> munlock option from __mlock_vma_pages_range(), and use a simple loop of
> follow_page()s in munlock_vma_pages_range() instead; ignoring absent
> pages, and not marking present pages as accessed or dirty.
>
> (Change munlock() to only go so far as mlock() reached?  That does not
> work out, given the convention that mlock() claims complete success even
> when it has to give up early - in part so that an underlying file can be
> extended later, and those pages locked which earlier would give SIGBUS.)
>
> Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>

Reviewed-by: Hiroaki Wakabayashi <primulaelatior@...il.com>

It very simple and so cool! I have learned something.

--
Thanks,
Hiroaki Wakabayashi
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