linux-kernel - Re: Tmem [PATCH 0/5] (Take 3): Transcendent memory

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Message-ID: <20091228205102.GC1637@ucw.cz>
Date:	Mon, 28 Dec 2009 21:51:03 +0100
From:	Pavel Machek <pavel@....cz>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
Cc:	Nitin Gupta <ngupta@...are.org>, Nick Piggin <npiggin@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>, jeremy@...p.org,
	xen-devel@...ts.xensource.com, tmem-devel@....oracle.com,
	Rusty Russell <rusty@...tcorp.com.au>,
	Rik van Riel <riel@...hat.com>, dave.mccracken@...cle.com,
	sunil.mushran@...cle.com, Avi Kivity <avi@...hat.com>,
	Schwidefsky <schwidefsky@...ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, chris.mason@...cle.com,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Tmem [PATCH 0/5] (Take 3): Transcendent memory

Hi!

> > achive this using
> > > > some existing infrastructure in kernel.
> > > 
> > > Hi Nitin --
> > > 
> > > Sorry if I sounded overly negative... too busy around the holidays.
> > > 
> > > I'm definitely OK with exploring alternatives.  I just think that
> > > existing kernel mechanisms are very firmly rooted in the notion
> > > that either the kernel owns the memory/cache or an asynchronous
> > > device owns it.  Tmem falls somewhere in between and is very
> > 
> > Well... compcache seems to be very similar to preswap: in preswap case
> > you don't know if hypervisor will have space, in ramzswap you don't
> > know if data are compressible.
> 
> Hi Pavel --
> 
> Yes there are definitely similarities too.  In fact, I started
> prototyping preswap (now called frontswap) with Nitin's
> compcache code.  IIRC I ran into some problems with compcache's
> difficulties in dealing with failed "puts" due to dynamic
> changes in size of hypervisor-available-memory.
> 
> Nitin may have addressed this in later versions of ramzswap.

That would be cool to find out.

> One feature of frontswap which is different than ramzswap is
> that frontswap acts as a "fronting store" for all configured
> swap devices, including SAN/NAS swap devices.  It doesn't
> need to be separately configured as a "highest priority" swap
> device.  In many installations and depending on how ramzswap

Ok, I'd call it a bug, not a feature :-).
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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