linux-kernel - Re: Frontswap [PATCH 0/4] (was Transcendent Memory): overview

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Message-ID: <20100502071059.GF1790@ucw.cz>
Date:	Sun, 2 May 2010 09:11:00 +0200
From:	Pavel Machek <pavel@....cz>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
Cc:	Avi Kivity <avi@...hat.com>, Jeremy Fitzhardinge <jeremy@...p.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	hugh.dickins@...cali.co.uk, ngupta@...are.org, JBeulich@...ell.com,
	chris.mason@...cle.com, kurt.hackel@...cle.com,
	dave.mccracken@...cle.com, npiggin@...e.de,
	akpm@...ux-foundation.org, riel@...hat.com
Subject: Re: Frontswap [PATCH 0/4] (was Transcendent Memory): overview


> So there are two users of frontswap for which the synchronous
> interface makes sense.  I believe there may be more in the
> future and you disagree but, as Jeremy said, "a general Linux
> principle is not to overdesign interfaces for hypothetical users,
> only for real needs."  We have demonstrated there is a need
> with at least two users so the debate is only whether the
> number of users is two or more than two.
> 
> Frontswap is a very non-invasive patch and is very cleanly
> layered so that if it is not in the presence of either of 
> the intended "users", it can be turned off in many different
> ways with zero overhead (CONFIG'ed off) or extremely small overhead
> (frontswap_ops is never set; or frontswap_ops is set but the
> underlying hypervisor doesn't support it so frontswap_poolid
> never gets set).

Yet there are less invasive solutions available, like 'add trim
operation to swap_ops'.

So what needs to be said here is 'frontswap is XX times faster than
swap_ops based solution on workload YY'.
								       Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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