linux-kernel - Re: [PATCH 0/9] Hugepage migration (v2)

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Date:	Mon, 16 Aug 2010 18:19:35 +0900
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	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>
Subject: Re: [PATCH 0/9] Hugepage migration (v2)

On Fri, Aug 13, 2010 at 07:47:21AM -0500, Christoph Lameter wrote:
> On Thu, 12 Aug 2010, Naoya Horiguchi wrote:
> 
> > > Can you also avoid refcounts being increased during migration?
> >
> > Yes. I think this will be done in above-mentioned refactoring.
> 
> Thats not what I meant. Can you avoid other processors increasing
> refcounts (direct I/O etc?) on any page struct of the huge page while
> migration is running?

In my understanding, in current code "other processors increasing refcount
during migration" can happen both in non-hugepage direct I/O and in hugepage
direct I/O in the similar way (i.e. get_user_pages_fast() from dio_refill_pages()).
So I think there is no specific problem to hugepage.
Or am I missing your point?

>
> > This patch only handles migration under direct I/O.
> > For the opposite (direct I/O under migration) it's not true.
> > I wrote additional patches (later I'll reply to this email)
> > for solving locking problem. Could you review them?
> 
> Sure.
> 
> > (Maybe these patches are beyond the scope of hugepage migration patch,
> > so is it better to propose them separately?)
> 
> Migration with known races is really not what we want in the kernel.

Yes.

Thanks,
Naoya Horiguchi
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