Subject: Re: [RFC] Hugetlb demotion for x86
From: Adam Litke <agl@us.ibm.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-mm@kvack.kernel.org, linux-kernel@vger.kernel.org
In-Reply-To: <20060510200516.GA30346@infradead.org>
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	 <20060510200516.GA30346@infradead.org>
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Organization: IBM
Date: Wed, 10 May 2006 15:32:36 -0500
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On Wed, 2006-05-10 at 21:05 +0100, Christoph Hellwig wrote:
> On Wed, May 10, 2006 at 01:56:40PM -0500, Adam Litke wrote:
> > The following patch enables demotion of MAP_PRIVATE hugetlb memory to
> > normal anonymous memory on the i386 architecture.
> 
> This is an awfully bad idea.  Applications should do smart fallback
> instead.  For the same reason we for example fail O_DIRECT requests
> we can fullfill instead of doing the half buffered I/O braindamage
> solaris does.

By smart fallback do you mean we should convert the hugetlb fault code
back to using VM_FAULT_SIGBUS and writing userspace sighandlers to do
the same thing I am, but in userspace?  FWIW I did implement that in
libhugetlbfs to try it out, but that seems much dirtier to me than
handling faults in the kernel.

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center

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