Date: Sat, 31 Jan 2009 22:27:55 +0100
From: Pavel Machek <pavel@suse.cz>
To: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Tim Small <tim@buttersideup.com>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       ncunningham-lkml@crca.org.au, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org, Chris Friesen <cfriesen@nortel.com>,
       Doug Thompson <norsk5@yahoo.com>, bluesmoke-devel@lists.sourceforge.net,
       Arjan van de Ven <arjan@infradead.org>
Subject: Re: marching through all physical memory in software
Message-ID: <20090131212754.GA15243@elf.ucw.cz>
References: <715599.77204.qm@web50111.mail.re2.yahoo.com> <m1wscc7fop.fsf@fess.ebiederm.org> <49836114.1090209@buttersideup.com> <m1iqnw1676.fsf@fess.ebiederm.org> <4984489C.8020309@buttersideup.com> <20090131134327.GB28763@khazad-dum.debian.net>
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Hi!

> And if an uncorretable error is detected during the scrub, we have to
> do something about it as well.  And that won't be that easy: locate
> whatever process is using that page, and so something smart to it...
> or do some emergency evasive actions if it is one of the kernel's data
> scructures, etc.
> 
> So, as you said, "background scrubbing" and "software scrubbing" really are
> very different things, and one has to expect that background scrubbing will
> eventually trigger software scrubbing, major system emergency handling
> (uncorrectable errors in kernel memory) or minor system emergency
> handling (uncorrectable errors in process memory).
> 
> > There is (AFAIK) no need to do any writes here, and in fact doing so is 
> 
> One might want the possibility of doing inconditional writes, because
> it helps with memory bitrot on crappy hardware where the refresh
> cycles aren't enough to avoid bitrot.  But you definately won't want
> it most of the time.
> 
> You can also implement software-based ECC using a background scrubber
> and setting aside pages to store the ECC information.  Now, THAT is
> probably not worth bothering with due to the performance impact, but
> who knows...

Actually, that would be quite cool. a) I suspect memory in  my zaurus
bitrots and b) bitroting memory over s2ram is apprently quite common.

									Pavel

-- 
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