Re: [patch] tracing/mm: add page frame snapshot trace

[Ingo Molnar]

* Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:

> Hi Ingo,
> 
> On Sat, May 09, 2009 at 02:27:58PM +0800, Ingo Molnar wrote:
> > 
> > * Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> > 
> > > > So this should be done in cooperation with instrumentation 
> > > > folks, while improving _all_ of Linux instrumentation in 
> > > > general. Or, if you dont have the time/interest to work with us 
> > > > on that, it should not be done at all. Not having the 
> > > > resources/interest to do something properly is not a license to 
> > > > introduce further instrumentation crap into Linux.
> > > 
> > > I'd be glad to work with you on the 'object collections' ftrace 
> > > interfaces.  Maybe next month. For now my time have been allocated 
> > > for the hwpoison work, sorry!
> > 
> > No problem - our offer still stands: we are glad to help out with 
> > the instrumentation side bits. We'll even write all the patches for 
> > you, just please help us out with making it maximally useful to 
> > _you_ :-)
> 
> Thank you very much!
> 
> The good fact is, 2/3 of the code and experiences can be reused.
> 
> > Find below a first prototype patch written by Steve yesterday and 
> > tidied up a bit by me today. It can also be tried on latest -tip:
> > 
> >   http://people.redhat.com/mingo/tip.git/README
> > 
> > This patch adds the first version of the 'object collections' 
> > instrumentation facility under /debug/tracing/objects/mm/. It has a 
> > single control so far, a 'number of pages to dump' trigger file:
> > 
> > To dump 1000 pages to the trace buffers, do:
> > 
> >   echo 1000 > /debug/tracing/objects/mm/pages/trigger
> > 
> > To dump all pages to the trace buffers, do:
> > 
> >   echo -1 > /debug/tracing/objects/mm/pages/trigger
> 
> That is not too intuitive, I'm afraid.

This was just a first-level approximation - and it matches the usual 
"0xffffffff means infinite" idiom.

How about changing it from 'trigger' to 'dump_range':

   echo "*" > /debug/tracing/objects/mm/pages/dump_range

being a shortcut for 'dump all'?

And:

   echo "1000 2000" > /debug/tracing/objects/mm/pages/dump_range

?

The '1000' is the offset where the dumping starts, and 2000 is the 
size of the dump.

	Ingo
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