linux-kernel - Re: [PATCH 0/2] hugepage: optimize page fault path locking

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Date:	Wed, 7 Aug 2013 18:21:28 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Davidlohr Bueso <davidlohr@...com>
Cc:	Davidlohr Bueso <davidlohr.bueso@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Michel Lespinasse <walken@...gle.com>,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	"AneeshKumarK.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hillf Danton <dhillf@...il.com>,
	Hugh Dickins <hughd@...gle.com>,
	David Gibson <david@...son.dropbear.id.au>,
	Eric B Munson <emunson@...bm.net>,
	Anton Blanchard <anton@...ba.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] hugepage: optimize page fault path locking

On Tue, Aug 06, 2013 at 05:08:04PM -0700, Davidlohr Bueso wrote:
> On Mon, 2013-07-29 at 15:18 +0900, Joonsoo Kim wrote:
> > On Fri, Jul 26, 2013 at 07:27:23AM -0700, Davidlohr Bueso wrote:
> > > This patchset attempts to reduce the amount of contention we impose
> > > on the hugetlb_instantiation_mutex by replacing the global mutex with
> > > a table of mutexes, selected based on a hash. The original discussion can 
> > > be found here: http://lkml.org/lkml/2013/7/12/428
> > 
> > Hello, Davidlohr.
> > 
> > I recently sent a patchset which remove the hugetlb_instantiation_mutex
> > entirely ('mm, hugetlb: remove a hugetlb_instantiation_mutex').
> > This patchset can be found here: https://lkml.org/lkml/2013/7/29/54
> > 
> > If possible, could you review it and test it whether your problem is
> > disappered with it or not?
> 
> This patchset applies on top of https://lkml.org/lkml/2013/7/22/96
> "[PATCH v2 00/10] mm, hugetlb: clean-up and possible bug fix", right?
> 
> AFAIK those changes are the ones Andrew picked up a few weeks ago and
> are now in linux-next, right? I was able to apply those just fine, but
> couldn't apply your 'remove a hugetlb_instantiation_mutex series' (IIRC
> pach 1/18 failed). I guess you'll send out a v2 anyway so I'll wait
> until then.
> 
> In any case I'm not seeing an actual performance issue with the
> hugetlb_instantiation_mutex, all I noticed was that under large DB
> workloads that make use of hugepages, such as Oracle, this lock becomes
> quite hot during the first few minutes of startup, which makes sense in
> the fault path it is contended. So I'll try out your patches, but, in
> this particular case, I just cannot compare with the lock vs without the
> lock situations.

Okay. I just want to know that lock contention is reduced by my patches
in the first few minutes of startup. I will send v2 soon.

Thanks.
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