linux-kernel - Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon

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Date:	Mon, 12 Apr 2010 17:33:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	sgunderson@...foot.com
Subject: Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the
 anon_vmas  of a mergeable VMA

On Tue, 2010-04-13 at 00:17 +0900, Minchan Kim wrote:
> > Concurrent reclaim/gup/whatever could still have a count out on the page
> > delaying the actual free beyond the tlb gather RCU section.
> 
> anon_vma lock is just valid in case of page_mapped.
> if reclaim/gup/whatever want to use anon_vma, it should check with page_mapped.
> And last put_page doesn't touch anon_vma for freeing the page so I
> think it's not a problem. Do I miss something?

Hmm, I think you're right. The race I was thinking of makes the
page_lock_anon_vma() RCU section overlap with that of the mmu_gather,
which ensures the thing is long enough, or hits the !_mapcount case.

I'm not sure there are other page->mapping users that are interesting.

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