Date: Wed, 16 Dec 2009 19:13:12 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "linux-mm@kvack.org" <linux-mm@kvack.org>, cl@linux-foundation.org,
       "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
       "mingo@elte.hu" <mingo@elte.hu>, minchan.kim@gmail.com
Subject: Re: [mm][RFC][PATCH 0/11] mm accessor updates.
Message-Id: <20091216191312.f4655dac.kamezawa.hiroyu@jp.fujitsu.com>
In-Reply-To: <20091216101107.GA15031@basil.fritz.box>
References: <20091216120011.3eecfe79.kamezawa.hiroyu@jp.fujitsu.com>
	<20091216101107.GA15031@basil.fritz.box>
Organization: FUJITSU Co. LTD.
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On Wed, 16 Dec 2009 11:11:07 +0100
Andi Kleen <andi@firstfloor.org> wrote:

> On Wed, Dec 16, 2009 at 12:00:11PM +0900, KAMEZAWA Hiroyuki wrote:
> > This is from Christoph Lameter's mm_accessor patch posted 5/Nov.
> > 
> > Replacing all access to mm->mmap_sem with mm-accessor functions as
> >  mm_read_lock,
> >  mm_write_lock,
> >  etc...
> > 
> > This kind of function allows us to improve page fault performance etc..
> > For example, skil down_read(mmap_sem) in some situation.
> > (as: http://marc.info/?l=linux-mm&m=125809791306459&w=2)
> 
> The problem is that it also slows down the writers, and we have
> some workloads where writing is the bottleneck.
> 
> I don't think this is the right trade off at this time.
> 
Maybe you don't see my patch. (above URL) no slow down to write side.
My one doesn't use percpu counter.

> Also the patches didn't fare too well in testing unfortunately.
> 
> I suspect we'll rather need multiple locks split per address
> space range.

This set doesn't include any changes of the logic. Just replace all mmap_sem.
I think this is good start point (for introducing another logic etc..)


Thanks,
-Kame

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