linux-kernel - Re: [PATCH 2/2] mm,migration: Fix race between shift_arg_pages and rmap_walk by guaranteeing rmap_walk finds PTEs created within the temporary stack

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Message-Id: <20100510104039.98332e67.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 10 May 2010 10:40:39 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] mm,migration: Fix race between shift_arg_pages and
 rmap_walk by guaranteeing rmap_walk finds PTEs created within the temporary
 stack

On Sun, 9 May 2010 18:32:32 -0700 (PDT)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 
> 
> On Sun, 9 May 2010, Linus Torvalds wrote:
> > 
> > So I never disliked that patch. I'm perfectly happy with a "don't migrate 
> > these pages at all, because they are in a half-way state in the middle of 
> > execve stack magic".
> 
> Btw, I also think that Mel's patch could be made a lot _less_ magic by 
> just marking that initial stack vma with a VM_STACK_INCOMPLETE_SETUP bit, 
> instead of doing that "maybe_stack" thing. We could easily make that 
> initial vma setup very explicit indeed, and then just clear that bit when 
> we've moved the stack to its final position.
> 

Hmm. vm_flags is still 32bit..(I think it should be long long)

Using combination of existing flags...

#define VM_STACK_INCOMPLETE_SETUP (VM_RAND_READ | VM_SEC_READ)

Can be used instead of checking mapcount, I think.

Thanks,
-Kame

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