linux-kernel - Re: [GIT PULL] mm: frontswap (for 3.2 window)

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Date:	Wed, 16 Nov 2011 09:49:59 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Pekka Enberg <penberg@...nel.org>,
	Cyclonus J <cyclonusj@...il.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Christoph Hellwig <hch@...radead.org>,
	David Rientjes <rientjes@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>, ngupta@...are.org,
	Chris Mason <chris.mason@...cle.com>, JBeulich@...ell.com,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Jonathan Corbet <corbet@....net>
Subject: Re: [GIT PULL] mm: frontswap (for 3.2 window)

On Tue, Nov 15, 2011 at 09:33:40AM -0800, Jeremy Fitzhardinge wrote:
> On 11/15/2011 08:29 AM, Rik van Riel wrote:
> > On 11/02/2011 05:14 PM, Dan Magenheimer wrote:
> >
> >> It occurs to me that batching could be done locally without
> >> changing the in-kernel "API" (i.e. frontswap_ops)... the
> >> guest-side KVM tmem-backend-driver could do the compression
> >> into guest-side memory and make a single
> >> hypercall=vmexit/vmenter whenever it has collected enough for
> >> a batch.
> >
> > That seems like the best way to do it, indeed.
> >
> > Do the current hooks allow that mode of operation,
> > or do the hooks only return after the entire operation
> > has completed?
> 
> The APIs are synchronous, but need only return once the memory has been
> dealt with in some way.  If you were batching before making a hypercall,
> then the implementation would just have to make a copy into its private
> memory and you'd have to make sure that lookups on batched but
> unsubmitted pages work.
> 
> (It's been a while since I've looked at these patches, but I'm assuming
> nothing fundamental has changed about them lately.)

Yup, what you describe is possible, and nothing fundamental has changed about
them.
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