Subject: Re: Testing RAM from userspace / question about memmap= arguments
From: Jon Masters <jonathan@jonmasters.org>
To: Matthew Bloch <matthew@bytemark.co.uk>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <fk8umh$n7o$1@ger.gmane.org>
References: <fk8umh$n7o$1@ger.gmane.org>
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Organization: World Organi[sz]ation Of Broken Dreams
Date: Thu, 20 Dec 2007 07:33:32 -0500
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On Tue, 2007-12-18 at 17:06 +0000, Matthew Bloch wrote:

> I can see a few potential problems, but since my understanding of the
> low-level memory mapping is muddy at best, I won't speculate; I'd just
> appreciate any more expert views on whether this does work, or could be
> made to work.

Yo,

I don't think your testing approach is thorough enough. Clearly (knowing
your line of business - as a virtual machine provider), you want to do
pre-production testing as part of your provisioning. I would suggest
instead of using mlock() from userspace of simply writing a kernel
module that does this for every page of available memory.

You could script it via a minimal userland, containing only busybox,
some form of SSH implementation, whatever.

Jon.

P.S. With the above, you could also know which pages were faulty, an
consequently play with some of the bad RAM patches to exclude faulty
pages from the virtual machines running on a given host... ;-)


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