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

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Date:	Thu,  8 Apr 2010 11:03:27 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com, Rik van Riel <riel@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	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, hannes@...xchg.org
Subject: Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmas of a mergeable VMA

Hi

Wow, your patch is very cool. I'm surprising such 20 lines patch makes
lots simplify.

> On Wed, 7 Apr 2010, Linus Torvalds wrote:
> > 
> > Yes. The failure point is too late to do anything really interesting with, 
> > and the old code also just causes a SIGBUS. My intention was to change the 
> > 
> > 	WARN_ONCE(!vma->anon_vma);
> > 
> > into returning that SIGBUS - which is not wonderful, but is no different 
> > from old failures.
> 
> Not SIGBUS, but VM_FAULT_OOM, of course.

Now pagefault don't insert anon_vma anymore, right? if so, SIGBUS is better.
Now SIGBUS and VM_FAULT_OOM make different result.

SIGBUS       -> kill current task
VM_FAULT_OOM -> invoke oom-killer (see pagefault_out_of_memory())

If current task can't recover proper anon_vma. we should just kill current
instead random highest badness process. otherwise !anon_vma process continue
to randomly invoke oom-killer.

Perhaps, I'm missing something.



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