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

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Message-ID: <72951.1272369145@localhost>
Date:	Tue, 27 Apr 2010 07:52:25 -0400
From:	Valdis.Kletnieks@...edu
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
Cc:	Avi Kivity <avi@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, jeremy@...p.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

On Sun, 25 Apr 2010 06:37:30 PDT, Dan Magenheimer said:

> While I admit that I started this whole discussion by implying
> that frontswap (and cleancache) might be useful for SSDs, I think
> we are going far astray here.  Frontswap is synchronous for a
> reason: It uses real RAM, but RAM that is not directly addressable
> by a (guest) kernel.

Are there any production boxes that actually do this currently? I know IBM had
'expanded storage' on the 3090 series 20 years ago, haven't checked if the
Z-series still do that.  Was very cool at the time - supported 900+ users with
128M of main memory and 256M of expanded storage, because you got the first
3,000 or so page faults per second for almost free.  Oh, and the 3090 had 2
special opcodes for "move page to/from expanded", so it was a very fast but
still synchronous move (for whatever that's worth).

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