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

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Message-ID: <4EC2A274.8080801@goop.org>
Date:	Tue, 15 Nov 2011 09:33:40 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Rik van Riel <riel@...hat.com>
CC:	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>,
	Konrad Wilk <konrad.wilk@...cle.com>,
	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 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.)

    J
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