Date: Sat, 27 Jul 2013 10:25:12 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Andy Lutomirski <luto@amacapital.net>
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>
Subject: Re: [PATCH] mm: Save soft-dirty bits on file pages
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On Fri, Jul 26, 2013 at 02:36:51PM -0700, Andy Lutomirski wrote:
> >> Unless I'm misunderstanding this, it's saving the bit in the
> >> non-present PTE.  This sounds wrong -- what happens if the entire pmd
> >
> > It's the same as encoding pgoff in pte entry (pte is not present),
> > but together with pgoff we save soft-bit status, later on #pf we decode
> > pgoff and restore softbit back if it was there, pte itself can't disappear
> > since it holds pgoff information.
> 
> Isn't that only the case for nonlinear mappings?

Andy, I'm somehow lost, pte either exist with file encoded, either not,
when pud/ptes are zapped and any access to it should cause #pf pointing
kernel to read/write data from file to a page, if it happens on write
the pte is obtaining dirty bit (which always set together with soft
bit).
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