linux-kernel - Re: [mm][RFC][PATCH 0/11] mm accessor updates.

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Message-ID: <20091216101107.GA15031@basil.fritz.box>
Date:	Wed, 16 Dec 2009 11:11:07 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, cl@...ux-foundation.org,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...e.hu" <mingo@...e.hu>, andi@...stfloor.org,
	minchan.kim@...il.com
Subject: Re: [mm][RFC][PATCH 0/11] mm accessor updates.

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.

Also the patches didn't fare too well in testing unfortunately.

I suspect we'll rather need multiple locks split per address
space range.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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