linux-kernel - Re: [PATCH 02/10] hugetlb: add allocate function for hugepage migration

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Message-ID: <20100923084919.GA5185@csn.ul.ie>
Date:	Thu, 23 Sep 2010 09:49:19 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Jun'ichi Nomura <j-nomura@...jp.nec.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, tony.luck@...el.com
Subject: Re: [PATCH 02/10] hugetlb: add allocate function for hugepage
	migration

On Wed, Sep 22, 2010 at 04:05:47PM -0500, Christoph Lameter wrote:
> On Wed, 8 Sep 2010, Naoya Horiguchi wrote:
> 
> > We can't use existing hugepage allocation functions to allocate hugepage
> > for page migration, because page migration can happen asynchronously with
> > the running processes and page migration users should call the allocation
> > function with physical addresses (not virtual addresses) as arguments.
> 
> Ummm... Some arches like IA64 need huge pages fixed at certain virtual
> addresses in which only huge pages exist. A vma is needed in order to be
> able to assign proper virtual address to the page.
> 

Are you sure about this case? The virtual address of the page being migrated
should not changed, only the physical address.

> How does that work with transparent huge pages anyways?
> 

IA-64 doesn't support transparent huge pages. Even if it did, this
change is about hugetlbfs, not transparent huge page support.

> This looks like its going to break IA64 hugepage support for good.

How?

> Maybe
> thats okay given the reduced significance of IA64? Certainly would
> simplify the code.
> 

Currently I'm not seeing how IA-64 gets broken.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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