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From: Andy Lutomirski <luto@amacapital.net>
Date: Fri, 26 Jul 2013 13:55:04 -0700
Message-ID: <CALCETrUJa-Y40vnb6YOPry0dCXb3zCQ0y19i2yHWdzKR75HUzg@mail.gmail.com>
Subject: Re: [PATCH] mm: Save soft-dirty bits on file pages
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        Pavel Emelyanov <xemul@parallels.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Matt Mackall <mpm@selenic.com>,
        Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>
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On Fri, Jul 26, 2013 at 1:18 PM, Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> Andy reported that if file page get reclaimed we loose soft-dirty bit
> if it was there, so save _PAGE_BIT_SOFT_DIRTY bit when page address
> get encoded into pte entry. Thus when #pf happens on such non-present
> pte we can restore it back.
>

Unless I'm misunderstanding this, it's saving the bit in the
non-present PTE.  This sounds wrong -- what happens if the entire pmd
(or whatever the next level is called) gets zapped?  (Also, what
happens if you unmap a file and map a different file there?)

--Andy
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