linux-kernel - Re: [PATCH 4/5] mm: soft-dirty bits for user memory changes tracking

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Message-ID: <51E04D1E.8060303@parallels.com>
Date:	Fri, 12 Jul 2013 22:38:22 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Glauber Costa <glommer@...allels.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Matt Mackall <mpm@...enic.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH 4/5] mm: soft-dirty bits for user memory changes tracking

On 07/11/2013 10:46 PM, Andy Lutomirski wrote:
> 
> Sorry I'm late to the party -- I didn't notice this until the lwn
> article this week.
> 
> How does this get munmap + mmap right?  mremap marks things soft-dirty,
> but unmapping and remapping seems like it will result in the soft-dirty
> bit being cleared.  For that matter, won't this sequence also end up wrong:
> 
>  - clear_refs
>  - Write to mapping
>  - Page and pte evicted due to memory pressure
>  - Read from mapping -- clean page faulted back in
>  - pte soft-dirty is now clear ?!?

Yes, it looks like this problem exists. I'll look what can be done about
it, thank you.

> --Andy

Pavel
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