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From: Arjan van de Ven <arjan@infradead.org>
To: Pekka Paalanen <pq@iki.fi>
Cc: Ingo Molnar <mingo@elte.hu>,
	Harvey Harrison <harvey.harrison@gmail.com>,
	linux-kernel@vger.kernel.org, Jan Beulich <jbeulich@novell.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Pavel Roskin <proski@gnu.org>,
	pq@iki.fi
Subject: Re: [PATCH v2] x86: Add a list for custom page fault handlers.
Date: Thu, 31 Jan 2008 08:15:07 -0800	[thread overview]
Message-ID: <20080131081507.5edcde10@laptopd505.fenrus.org> (raw)
In-Reply-To: <20080131180253.6c007852@daedalus.pq.iki.fi>

On Thu, 31 Jan 2008 18:02:53 +0200
Pekka Paalanen <pq@iki.fi> wrote:

> > could you please send us a patch for the whole mmiotrace
> > kernel-side feature, so that we can have a look at the general
> > structure of this? (and the interaction with change_page_attr(),
> > etc.) Even if it's not functional (and wont even build/boot) at the
> > moment. Thanks,
> 
> Very well, first the revised custom page fault handler patch.
> Changes since the previous submit:
> - use spin_lock_irqsave instead of spin_lock
> - Harvey Harrison's clean-up with the #ifdefs
> - handler call site moved earlier
> - remove sync RCU call
> 
> I'm not aware of any functional problems with this one.
> 
> Arjan, you said you don't like this. May I ask why?

it's overhead that's rarely used, and worse, it suffers from the LSM disease:
it's a hook without visibility into the callers. Esp if there's only 1 user, a direct call
is not only faster, it also shows you what is going on when you're reading the code.
THe page fault stuff is tricky enough as it is without any "call arbitrary thing" hooks into
it

> This is most convinient for mmiotrace as it is meant to be a module.

that's not per se mutually exclusive, there's other cases like this already
(but even then, I don't want to go through hoops to make mmiotracing a module;
for me I can totally see it becoming a full mature member of the kernel, and if
that means a few things have to be changed in the normal kernel, or infrastructure
added, I'm totally ok with that)

> I'm also using this as an excuse to let other people to get into the
> page fault handler with their out-of-tree-today modules.

this is exactly the point.. it becomes a totally opaque thing, a random hook.


-- 
If you want to reach me at my work email, use arjan@linux.intel.com
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org

  reply	other threads:[~2008-01-31 16:15 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-27 16:52 [PATCH] " Pekka Paalanen
2008-01-27 17:55 ` [RFC PATCH] x86: mmiotrace - trace memory mapped IO Pekka Paalanen
2008-01-30 22:39   ` Pekka Paalanen
2008-01-27 19:29 ` [PATCH] x86: Add a list for custom page fault handlers Ingo Molnar
2008-01-27 21:03 ` Peter Zijlstra
2008-01-30  2:28 ` Harvey Harrison
2008-01-30  2:34   ` Harvey Harrison
2008-01-30 18:08     ` Pekka Paalanen
2008-01-31 15:07       ` Ingo Molnar
2008-01-31 16:02         ` [PATCH v2] " Pekka Paalanen
2008-01-31 16:15           ` Arjan van de Ven [this message]
2008-02-03  6:55             ` Pekka Paalanen
2008-02-03  7:03               ` Ingo Molnar
2008-02-03 21:40                 ` Pekka Paalanen
2008-02-05 20:28                 ` [PATCH 1/4] x86 mmiotrace: use lookup_address() Pekka Paalanen
2008-02-05 20:30                   ` [PATCH 2/4] x86 mmiotrace: fix relay-buffer-full flag for SMP Pekka Paalanen
2008-02-05 20:44                     ` Eric Dumazet
2008-02-05 21:14                       ` Pekka Paalanen
2008-02-05 21:35                         ` Eric Dumazet
2008-02-09 17:53                           ` [PATCH] x86 mmiotrace: Use percpu instead of arrays Pekka Paalanen
2008-02-05 20:31                   ` [PATCH 3/4] x86 mmiotrace: comment about user space ABI Pekka Paalanen
2008-02-05 20:39                   ` [PATCH 4/4] x86 mmiotrace: move files into arch/x86/mm/ Pekka Paalanen
2008-02-06  3:02                     ` Randy Dunlap
2008-02-09 11:21                       ` Pekka Paalanen
2008-02-07 12:53                     ` Ingo Molnar
2008-02-07 12:56                       ` Christoph Hellwig
2008-02-09 17:52                         ` [RFC PATCH] x86: explicit call to mmiotrace in do_page_fault() Pekka Paalanen
2008-02-09 18:01                           ` Arjan van de Ven
2008-02-09 18:23                             ` Pekka Paalanen
2008-02-09 18:56                               ` Pekka Enberg
2008-02-09 19:11                                 ` Pekka Paalanen
2008-02-09 19:19                                   ` Pekka Enberg
2008-02-09 18:39                             ` Peter Zijlstra
2008-02-09 18:39                           ` Peter Zijlstra
2008-02-10 18:05                             ` [RFC PATCH v2] " Pekka Paalanen
2008-02-11  2:12                               ` Pavel Roskin
2008-02-11 18:04                                 ` Pekka Paalanen
2008-02-06  5:00                   ` [PATCH 1/4] x86 mmiotrace: use lookup_address() Christoph Hellwig
2008-02-07 12:52                     ` Ingo Molnar
2008-01-31 16:16           ` [RFC PATCH v2] x86: mmiotrace - trace memory mapped IO Pekka Paalanen
2008-01-31 16:29             ` Arjan van de Ven
2008-02-03  7:21               ` Pekka Paalanen
2008-01-30 18:20 ` [PATCH] x86: Add a list for custom page fault handlers Arjan van de Ven

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