linux-kernel - Re: [Patch] mm tracepoints

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Date:	Fri, 06 Mar 2009 14:06:14 -0500
From:	Larry Woodman <lwoodman@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, fweisbec@...il.com
Subject: Re: [Patch] mm tracepoints

On Fri, 2009-03-06 at 18:38 +0100, Peter Zijlstra wrote:
> On Fri, 2009-03-06 at 18:10 +0100, Ingo Molnar wrote:
> > Looks pretty good and useful to me. I've Cc:-ed more mm folks, 
> > it would be nice to hear their opinion about these tracepoints.
> > 
> > Andrew, Nick, Peter, what do you think?
> 
> Bit sad we use the struct mm_struct * as mm identifier (little %lx vs %p
> confusion there too), but I suppose there simply isn't anything better.
> 
> Exposing kernel pointers like that might upset some of the security
> folks, not sure if I care though.
> 
> I'm missing the fault_filemap_read counterpart of fault_anon_pgin.

filemap_fault handles both the initial fault when the pte is zero and
pagein when the page has been reclaimed.  It was impossible to implement
them as separate handlers in __do_fault() without changing the
underlying MM code.

> 
> Once you have anon/filemap symmetric, you might consider folding these
> and doing the anon argument thing you do elsewhere.
> 
> Initially I was thinking we lacked the kswapd vs direct reclaim
> information on the pgout data, but since we log the pid:comm for each
> event...

They are separate, trace_mm_kswapd_runs() and
trace_mm_directreclaim_reclaimall().
trace_mm_directreclaim_reclaimzone() is for the zone_reclaim path where
we do local zone reclamation rather than falling off to the next zone in
the zone list.

> 
> Which brings us to mm_pdflush_*, we can already see its pdflush from
> pid:comm, then again, it fits the naming style. Same for
> mm_directreclaim*() - we already know its direct, since its not kswapd
> doing it.
> 

Like I said above there are 2 direct reclaim paths: one is teh call to
try_to_free_pages() out of __alloc_pages_internal() and the other is the
call to shrink_zone() out of __zone_reclaim().  I made a distinction
between these because the first calls shrink_zone for each zone in the
zone list when memory is really low(below min) where the second calls
shrink_zone for the local zone to prevent memory allocation from a
remote node.

> Finally, we have page_free, but not page_alloc? Oh, it is there, just
> not in the obvious place.

In order to get the zone free information it has to be in down in
get_page_from_freelist.

> 
> 
> Things missing, we trace unmap, but not mmap, mprotect, mlock?
> 
I was concentrating more on the operations that traced a page moving
throughout the system.  mmap and mprotect operate on the virtual address
space instead of the pages mapped in that address space.

Larry

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