linux-kernel - Re: [rfc] object collection tracing (was: [PATCH 5/5] proc: export more page flags in /proc/kpageflags)

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Date:	Sun, 17 May 2009 22:12:05 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Li Zefan <lizf@...fujitsu.com>,
	Tom Zanussi <tzanussi@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andi Kleen <andi@...stfloor.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Larry Woodman <lwoodman@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Matt Mackall <mpm@...enic.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [rfc] object collection tracing (was: [PATCH 5/5] proc: export
	more page flags in /proc/kpageflags)

On Sun, May 17, 2009 at 09:55:12PM +0800, Frederic Weisbecker wrote:
> On Sun, May 17, 2009 at 09:36:59PM +0800, Wu Fengguang wrote:
> > On Tue, May 12, 2009 at 09:01:12PM +0800, Frederic Weisbecker wrote:
> > > On Tue, Apr 28, 2009 at 09:31:08PM +0800, Wu Fengguang wrote:
> > > > On Tue, Apr 28, 2009 at 08:17:51PM +0800, Ingo Molnar wrote:
> > > >
> > > > There are two possible challenges for the conversion:
> > > >
> > > > - One trick it does is to select different lists to traverse on
> > > >   different filter options. Will this be possible in the object
> > > >   tracing framework?
> > >
> > > Yeah, I guess.
> >
> > Great.
> >
> > >
> > > > - The file name lookup(last field) is the performance killer. Is it
> > > >   possible to skip the file name lookup when the filter failed on the
> > > >   leading fields?
> > >
> > > objects collection lays on trace events where filters basically ignore
> > > a whole entry in case of non-matching. Not sure if we can easily only
> > > ignore one field.
> > >
> > > But I guess we can do something about the performances...
> >
> > OK, but it's not as important as the previous requirement, so it could
> > be the last thing to work on :)
> >
> > > Could you send us the (sob'ed) patch you made which implements this.
> > > I could try to adapt it to object collection.
> >
> > Attached for your reference. Be aware that I still have plans to
> > change it in non trivial way, and there are ongoing works by Nick(on
> > inode_lock) and Jens(on s_dirty) that can create merge conflicts.
> > So basically it is not a right time to do the adaption.
> 
> 
> Ah ok, so I will wait a bit :-)
> 
> 
> > However we can still do something to polish up the page object
> > collection under /debug/tracing/objects/mm/pages/. For example,
> > the timestamps and function name could be removed from the following
> > list :)
> >
> > # tracer: nop
> > #
> > #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
> > #              | |       |          |         |
> >            <...>-3743  [001]  3035.649769: dump_pages: pfn=1 flags=400 count=1 mapcount=0 index=0
> >            <...>-3743  [001]  3044.176403: dump_pages: pfn=1 flags=400 count=1 mapcount=0 index=0
> >            <...>-3743  [001]  3044.176407: dump_pages: pfn=2 flags=400 count=1 mapcount=0 index=0
> >            <...>-3743  [001]  3044.176408: dump_pages: pfn=3 flags=400 count=1 mapcount=0 index=0
> >            <...>-3743  [001]  3044.176409: dump_pages: pfn=4 flags=400 count=1 mapcount=0 index=0
> >            <...>-3743  [001]  3044.176409: dump_pages: pfn=5 flags=400 count=1 mapcount=0 index=0
> >            <...>-3743  [001]  3044.176410: dump_pages: pfn=6 flags=400 count=1 mapcount=0 index=0
> >            <...>-3743  [001]  3044.176410: dump_pages: pfn=7 flags=400 count=1 mapcount=0 index=0
> >            <...>-3743  [001]  3044.176411: dump_pages: pfn=8 flags=400 count=1 mapcount=0 index=0
> >            <...>-3743  [001]  3044.176411: dump_pages: pfn=9 flags=400 count=1 mapcount=0 index=0
> >            <...>-3743  [001]  3044.176412: dump_pages: pfn=10 flags=400 count=1 mapcount=0 index=0
> 
> 
> echo nocontext-info > /debug/tracing/trace_options :-)

Nice tip - I should really learn more about ftrace :-)

> But you'll have only the function and the pages specifics. It's not really the
> function but more specifically the name of the event. It's useful to distinguish
> multiple events to a trace.
> 
> Hmm, may be it's not that much useful in a object dump...

Yeah - and to enable that option automatically in relevant code :)

Thanks,
Fengguang
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