linux-kernel - Re: [PATCH] mm/hugetlb: per-vma instantiation mutexes

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Message-ID: <20130716080026.GA8925@voom.fritz.box>
Date:	Tue, 16 Jul 2013 18:00:26 +1000
From:	David Gibson <david@...son.dropbear.id.au>
To:	Davidlohr Bueso <davidlohr.bueso@...com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Michel Lespinasse <walken@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Michal Hocko <mhocko@...e.cz>,
	"AneeshKumarK.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hillf Danton <dhillf@...il.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Anton Blanchard <anton@...ba.org>
Subject: Re: [PATCH] mm/hugetlb: per-vma instantiation mutexes

On Mon, Jul 15, 2013 at 05:12:31PM -0700, Davidlohr Bueso wrote:
> On Mon, 2013-07-15 at 16:08 -0700, Andrew Morton wrote:
> > On Mon, 15 Jul 2013 17:24:32 +1000 David Gibson <david@...son.dropbear.id.au> wrote:
> > 
> > > I have previously proposed a correct method of improving scalability,
> > > although it doesn't eliminate the lock.  That's to use a set of hashed
> > > mutexes.
> > 
> > Yep - hashing the mutexes is an obvious and nicely localized way of
> > improving this.  It's a tweak, not a design change.
> > 
> > The changelog should describe the choice of the hash key with great
> > precision, please.  It's important and is the first thing which
> > reviewers and readers will zoom in on.

Yeah, that is important.

I no longer have much interest in the result of this patch, so I'll
leave it to others to do the forward port and cleanup.

But I will point out the gotcha here is that the hash key needs to be
based on (address_space & file offset) for MAP_SHARED, but (mm &
address) for MAP_PRIVATE.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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