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

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Date:	Tue, 06 Aug 2013 17:08:04 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	Joonsoo Kim <iamjoonsoo.kim@....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 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.

Thanks,
Davidlohr

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