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Date:	Mon, 09 Sep 2013 10:34:45 +0800
From:	Daniel J Blueman <daniel@...ascale.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
CC:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Andi Kleen <andi@...stfloor.org>,
	Michal Hocko <mhocko@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	kirill.shutemov@...ux.intel.com,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Alex Thorlton <athorlton@....com>,
	Steffen Persvold <sp@...ascale.com>
Subject: Re: [PATCH 2/2] thp: support split page table lock

On Saturday, 7 September 2013 02:10:02 UTC+8, Naoya Horiguchi  wrote:
> Hi Alex,
>
> On Fri, Sep 06, 2013 at 11:04:23AM -0500, Alex Thorlton wrote:
> > On Thu, Sep 05, 2013 at 05:27:46PM -0400, Naoya Horiguchi wrote:
> > > Thp related code also uses per process mm->page_table_lock now.
> > > So making it fine-grained can provide better performance.
> > >
> > > This patch makes thp support split page table lock by using page->ptl
> > > of the pages storing "pmd_trans_huge" pmds.
> > >
> > > Some functions like pmd_trans_huge_lock() and
page_check_address_pmd()
> > > are expected by their caller to pass back the pointer of ptl, so this
> > > patch adds to those functions new arguments for that. Rather than
that,
> > > this patch gives only straightforward replacement.
> > >
> > > ChangeLog v3:
> > >  - fixed argument of huge_pmd_lockptr() in copy_huge_pmd()
> > >  - added missing declaration of ptl in do_huge_pmd_anonymous_page()
> >
> > I've applied these and tested them using the same tests program that I
> > used when I was working on the same issue, and I'm running into some
> > bugs.  Here's a stack trace:
>
> Thank you for helping testing. This bug is new to me.

With 3.11, this patch series and CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS, I 
consistently hit the same failure when exiting one of my stress-testers 
[1] when using eg 24 cores.

Doesn't happen with 8 cores, so likely needs enough virtual memory to 
use multiple split locks. Otherwise, this is very promising work!

[1] http://quora.org/2013/fft3d.c
-- 
Daniel J Blueman
Principal Software Engineer, Numascale
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