linux-kernel - Re: [PATCH] mm: Save soft-dirty bits on file pages

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Message-ID: <20130727062512.GC8508@moon>
Date:	Sat, 27 Jul 2013 10:25:12 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH] mm: Save soft-dirty bits on file pages

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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