linux-kernel - Re: [patch 6/6] Guest page hinting: s390 support.

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Message-Id: <1205400746.26537.20.camel@localhost>
Date:	Thu, 13 Mar 2008 10:32:26 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Anthony Liguori <anthony@...emonkey.ws>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	virtualization@...ts.osdl.org, akpm@...l.org,
	nickpiggin@...oo.com.au, frankeh@...son.ibm.com, hugh@...itas.com
Subject: Re: [patch 6/6] Guest page hinting: s390 support.

On Wed, 2008-03-12 at 15:04 -0500, Anthony Liguori wrote:
> Jeremy Fitzhardinge wrote:
> >> With stable_if_clean you are refering to stable_if_present?
> > 
> > No.  I misunderstood and thought that stable_if_present sets the Px 
> > state.  I'd overlooked the writable flag on page_set_volatile().
> > 
> >>  If yes the
> >> answer is that this operation is used to get a page from Vx/Px back to
> >> Sx but only if the page has not been discarded.
> > 
> > So you mean it will change Vr/Pr to Sr but everything else will fail?  

In the extended version Vp/Pp to Sr as well but the current z/VM code
will discard a page if the host picks a Vr/Pr page to swap it.

> Well presumably Vp/Pr => Sp?  Is is true that from the guest's 
> perspective, all of the 'p' states are identical to the 'r' states?

Basically yes. The guest doesn't care about the host state.

> Do the host states even really need visibility to the guest at all?  It 
> may be useful for the guest to be able to distinguish between Ur and Uz 
> but it doesn't seem necessary.

It is very useful for debugging to have the host state in the guest as
well. There is one possible optimization: if the guests finds a Uz page
in the free list, it can make it Sz and doesn't have to clear it because
the host will provide an already empty page (not yet implemented
though).

> BTW Jeremy, the .dot was very useful!

I've search on my disk and found the state diagrams we've used for the
OLS paper. You may find these useful as well.

-- 
blue skies,
  Martin.

"Reality continues to ruin my life." - Calvin.


Download attachment "states.dia" of type "application/x-dia-diagram" (5973 bytes)

Download attachment "states-simple.dia" of type "application/x-dia-diagram" (3966 bytes)