netdev - RE: [RFC] non-preemptible kernel socket for RAMster

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Message-ID: <6147447c-ecab-43ea-9b4a-1ff64b2089f0@default>
Date:	Tue, 5 Jul 2011 10:25:21 -0700 (PDT)
From:	Dan Magenheimer <dan.magenheimer@...cle.com>
To:	"Loke, Chetan" <Chetan.Loke@...scout.com>, netdev@...r.kernel.org
Cc:	Konrad Wilk <konrad.wilk@...cle.com>, linux-mm <linux-mm@...ck.org>
Subject: RE: [RFC] non-preemptible kernel socket for RAMster

> From: Loke, Chetan [mailto:Chetan.Loke@...scout.com]
> Sent: Tuesday, July 05, 2011 10:37 AM
> To: Dan Magenheimer; netdev@...r.kernel.org
> Cc: Konrad Wilk; linux-mm
> Subject: RE: [RFC] non-preemptible kernel socket for RAMster
> 
> > In working on a kernel project called RAMster* (where RAM on a
> > remote system may be used for clean page cache pages and for swap
> > pages), I found I have need for a kernel socket to be used when
> 
> How is RAMster+swap different than NBD's (pending etc?)support for SWAP
> over NBD?

Hi Chetan --

Thanks for your question.

I may be ignorant of details about NBD, but did some quick
research using google.  If I understand correctly, swap over
NBD is still writing to a configured swap disk on the remote
machine.  RAMster is swapping to *RAM* on the remote machine.
The idea is that most machines are very overprovisioned in
RAM, and are rarely using all of their RAM, especially when
a machine is (mostly) idle.  In other words, the "max of
the sums" of RAM usage on a group of machines is much lower
than the "sum of the max" of RAM usage.

So if the network is sufficiently faster than disk for
moving a page of data, RAMster provides a significant
performance improvement.  OR RAMster may allow a significant
reduction in the total amount of RAM across a data center.

The version of RAMster I am working on now is really
a proof-of-concept that works over sockets, using the
ocfs2 cluster layer.  One can easily envision a future
"exo-fabric" which allows one machine to write to the
RAM of another machine... for this future hardware,
RAMster becomes much more interesting.

Thanks,
Dan
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