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

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Message-ID: <20130724185256.GA24365@moon>
Date:	Wed, 24 Jul 2013 22:52:56 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	James Bottomley <James.Bottomley@...senpartnership.com>,
	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 swapped pages

On Wed, Jul 24, 2013 at 11:21:46AM -0700, Andy Lutomirski wrote:
> >
> > I fear for tracking soft-dirty-bit for swapped entries we sinply have
> > no other place than pte (still i'm quite open for ideas, maybe there
> > are a better way which I've missed).
> 
> I know approximately nothing about how swap and anon_vma work.
> 
> For files, sticking it in struct page seems potentially nicer,
> although finding a free bit might be tough.  (FWIW, I have plans to
> free up a page flag on x86 some time moderately soon as part of a
> completely unrelated project.)  I think this stuff really belongs to
> the address_space more than it belongs to the pte.

Well, some part of information already lays in pte (such as 'file' bit,
swap entries) so it looks natural i think to work on this level. but
letme think if use page struct for that be more convenient...

> 
> How do you handle the write syscall?

I fear I somehow miss your point here, could please alaborate a bit?
There is no additional code I know of being write() specific, just
a code for #PF exceptions.
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