linux-kernel - Re: [PATCH 0/2] ia64: Migrate data off physical pages with correctable errors

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Message-ID: <20080428203609.GB23847@sgi.com>
Date:	Mon, 28 Apr 2008 15:36:09 -0500
From:	Russ Anderson <rja@....com>
To:	Matthew Wilcox <matthew@....cx>
Cc:	linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>,
	Christoph Lameter <clameter@....com>
Subject: Re: [PATCH 0/2] ia64: Migrate data off physical pages with correctable errors

On Mon, Apr 28, 2008 at 01:33:23PM -0600, Matthew Wilcox wrote:
> On Mon, Apr 28, 2008 at 02:22:52PM -0500, Russ Anderson wrote:
> > 	There is always an issue of how agressive the code should be on
> > 	migrating pages.  Should it migrate on the first correctable error,
> > 	or wait for some threshold?  Reasonable people may disagree on the
> > 	threshold and the "right" answer may be hardware specific.  The 
> > 	decision making is confined to the cpe_migrate.c code.  It is
> > 	currently set to migrate on the first correctable error.
> 
> I think the kernel code should do the migration ASAP.  But I think we
> should have a list of 'bad' pages.  We could then have a badram driver
> that userspace can talk to to find out which pages are bad, map those
> pages into a badram process, do various tests on them, and return the
> pages to the pool if they're determined to be 'good'.

Sure.  The bad page list is badpagelist (defined in mca.c).
 
> I could also see badramd having a list of pages found to be bad
> in previous boots and asking the badram driver to take them out of
> circulation early in boot before they've been allocated.

That would be one alternative.  That type functionality would be
useful.  FWIW, some of my testing was on a system with a DIMM with
solid single bits.  It is a row/column problem so several meg of
addresses are effected.  Each boot it would migrate several meg worth
of pages without any problem.  It works surprisingly good.

-- 
Russ Anderson, OS RAS/Partitioning Project Lead  
SGI - Silicon Graphics Inc          rja@....com
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