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Date: Fri, 5 Mar 2004 00:24:18 +0100
From: Andrea Arcangeli <andrea@suse.de>
To: Rik van Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@osdl.org>, Peter Zaitsev <peter@mysql.com>,
       mbligh@aracnet.com, linux-kernel@vger.kernel.org
Subject: Re: 2.4.23aa2 (bugfixes and important VM improvements for the high end)
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On Thu, Mar 04, 2004 at 05:14:30PM -0500, Rik van Riel wrote:
> > or maybe you mean the page_table_lock hold during copy-user that Andrew
> > mentioned? (copy-user doesn't mean "all VM operations" not sure if you
> > meant this or the usual locking of every 2.4/2.6 kernel out there)
> 
> True, there are some other operations.  However, when

could you name one that is serialized in 4:4 and not in 3:1 with an mm
lock? just curious. there are tons of VM operations serialized by the
page_table_lock that hurts with threads in 3:1 too. I understood only
copy-user needs the additional locking.

> you consider the fact that copy-user operations are
> needed for so many things they are the big bottleneck.
> 
> Making it possible to copy things to and from userspace
> in a lockless way will help performance quite a bit...

I don't expect an huge speedup but certainly it would be measurable.