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Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management)
- From: Ingo Molnar <mingo at elte dot hu>
- To: Mathieu Desnoyers <compudj at krystal dot dyndns dot org>
- 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 18:53:52 +0200
- 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>
* 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?)