Re: [Patch] mm tracepoints

Larry Woodman
2009-03-06T19:03:21Z

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