linux-kernel - Re: LTTng do_page_fault vs handle_mm

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Date:	Tue, 21 Nov 2006 19:26:02 +0300
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	ltt-dev@...fik.org, mgreer@...sta.com, mlachwani@...sta.com
Subject: Re: LTTng do_page_fault vs handle_mm_fault instrumentation

Hello.

Mathieu Desnoyers wrote:

> I would like to discuss your suggestion of moving the do_page_fault
> instrumentation to handle_mm_fault. On one side, it helps removing architecture
> dependant instrumentation, but on the other hand :

> 1- We cannot access the struct pt_regs in all cases (there may be an invalid
>    current task struct).
> 2- We cannot distinguish between calls to handle_mm_fault from the page fault
>    handler or from get_user_pages.
> 3- Some people complain about not having enough information about the cause of
>    the page fault (see the forward below).
> 
> So instead of staying between my users who ask for those feature and kernel
> developers who wish to reduce the intrusiveness of instrumentation (which is a
> nice goal : moving the syscall entry/exit instrumentation do do_syscall_trace
> has helped simplifying the instrumentation), I prefer to open the discussion
> about it.

    It seems I've missed the whole story behind this move.
    For me, it was more a question of consistency: if we're trying to trace 
all trap handlers, why not page fault one? So, I just wanted my old LTT 
tracepoints back. :-)

> Ideas/comments are welcome.

> Regards,

> Mathieu

WBR, Sergei
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