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Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management)
- From: Mathieu Desnoyers <compudj at krystal dot dyndns dot org>
- To: Ingo Molnar <mingo at elte dot hu>
- Cc: Martin Bligh <mbligh at google dot com>, "Frank Ch. Eigler" <fche at redhat dot com>, Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, prasanna at in dot ibm dot com, Andrew Morton <akpm at osdl dot org>, Paul Mundt <lethal at linux-sh dot org>, linux-kernel <linux-kernel at vger dot kernel dot org>, Jes Sorensen <jes at sgi dot com>, Tom Zanussi <zanussi at us dot ibm dot com>, Richard J Moore <richardj_moore at uk dot ibm dot com>, Michel Dagenais <michel dot dagenais at polymtl dot ca>, Christoph Hellwig <hch at infradead dot org>, Greg Kroah-Hartman <gregkh at suse dot de>, Thomas Gleixner <tglx at linutronix dot de>, William Cohen <wcohen at redhat dot com>, ltt-dev at shafik dot org, systemtap at sources dot redhat dot com, Alan Cox <alan at lxorguk dot ukuu dot org dot uk>
- Date: Fri, 22 Sep 2006 13:11:56 -0400
- Subject: Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management)
- References: <20060921160009.GA30115@Krystal> <20060921160656.GA24774@elte.hu> <20060921214248.GA10097@Krystal> <20060922064955.GA4167@elte.hu> <20060922140329.GA20839@Krystal> <20060922165352.GA16476@elte.hu>
* Ingo Molnar (firstname.lastname@example.org) wrote:
> * Mathieu Desnoyers <email@example.com> wrote:
> > > > Then you lose the ability to trace in-kernel minor page faults.
> > >
> > > that's wrong, minor pagefaults go through __handle_mm_fault() just as
> > > much.
> > >
> > Hi Ingo,
> > On a 2.6.17 kernel tree :
> > It seems like a shortcut path that will never call __handle_mm_fault.
> > This path is precisely used to handle vmalloc faults.
> yes, but you said "minor fault", not "vmalloc fault".
> minor faults are the things that happen when a task does read-after-COW
> or read-mmap-ed-pagecache-page, and they very much go through
> vmalloc faults are extremely rare, x86-specific and they are a pure
> kernel-internal matter. (I'd never want to trace them, especially if it
> pushes tracepoints into every architecture's page fault handler. I
> implemented the initial version of them IIRC, but my memory fails
> precisely why. I think it was 4:4 related, but i'm unsure.)
> (i now realize that above you said "in-kernel minor faults" - under that
> you meant vmalloc faults?)
Yes, sorry, my mistake. This kind of fault is not as infrequent as you may
think, as every newly allocated vmalloc region will cause vmalloc faults on
every processes on the system that are trying to access them. I agree that
it should not be a standard event people would be interested in.
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