Date: Thu, 17 Nov 2005 08:43:32 -0600
From: Robin Holt <holt@sgi.com>
To: Christoph Lameter <clameter@engr.sgi.com>
Cc: Robin Holt <holt@sgi.com>, Mel Gorman <mel@csn.ul.ie>,
       Russ Anderson <rja@sgi.com>, linux-kernel@vger.kernel.org
Subject: Re: How to handle a hugepage with bad physical memory?
Message-ID: <20051117144332.GC4316@lnx-holt.americas.sgi.com>
References: <20051116131012.GE4573@lnx-holt.americas.sgi.com> <Pine.LNX.4.62.0511161155380.16434@schroedinger.engr.sgi.com>
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On Wed, Nov 16, 2005 at 11:58:13AM -0800, Christoph Lameter wrote:
> On Wed, 16 Nov 2005, Robin Holt wrote:
> 
> > Russ Anderson recently introduced a patch into ia64 that changes MCA
> > behavior.  When the MCA is caused by a user reference to a users memory,
> > we put an extra reference on the page and kill the user.  This leaves
> > the working memory available for other jobs while causing a leak of the
> > bad page.
> > 
> > I don't know if Russ has done any testing with hugetlbfs pages.  I preface
> > the remainder of my comments with a huge "I don't know anything"
> > disclaimer.
> > 
> > With the new hugepages concept, would it be possible to only mark
> > the default pagesize portion of a hugepage as bad and then return the
> > remainder of the hugepage for normal use?  What would we basically need
> > to do to accomplish this?  Are there patches in the community which we
> > should wait to see how they progress before we do any work on this front?
> 
> On IA64 we have one PTE for a huge page in a different region, so we 
> cannot unmap a page sized section. Other architectures may have PTEs for 
> each page sized section of a huge page. For those it may make sense 
> (but then the management of the page is done via the first page_struct, 
> which likely results in some challenging VM issues).

Christoph,

I think you misunderstood me.  I was talking about killing the process.
All the mappings get destroyed.  I want to reclaim as much of that huge
page as possible.

Once everything is cleared up, I would like to break the huge page back
into normal-size pages and free those.

Thanks,
Robin
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