Re: [PATCH V2 2/7] mm/gup: add gup trace points

[Shi, Yang]

On 12/2/2015 4:11 PM, Shi, Yang wrote:
> On 12/2/2015 3:36 PM, Dave Hansen wrote:
> > On 12/02/2015 02:53 PM, Yang Shi wrote:
> > > diff --git a/mm/gup.c b/mm/gup.c
> > > index deafa2c..10245a4 100644
> > > --- a/mm/gup.c
> > > +++ b/mm/gup.c
> > > @@ -13,6 +13,9 @@
> > >   #include <linux/rwsem.h>
> > >   #include <linux/hugetlb.h>
> > >
> > > +#define CREATE_TRACE_POINTS
> > > +#include <trace/events/gup.h>
> > > +
> > >   #include <asm/pgtable.h>
> > >   #include <asm/tlbflush.h>
> >
> > This needs to be _the_ last thing that gets #included.  Otherwise, you
> > risk colliding with any other trace header that gets implicitly included
> > below.
>
> Thanks for the suggestion, will move it to the last.
>
> > > @@ -1340,6 +1346,8 @@ int __get_user_pages_fast(unsigned long start,
> > > int nr_pages, int write,
> > >                       start, len)))
> > >           return 0;
> > >
> > > +    trace_gup_get_user_pages_fast(start, nr_pages, write, pages);
> > > +
> > >       /*
> > >        * Disable interrupts.  We use the nested form as we can
> > > already have
> > >        * interrupts disabled by get_futex_key.
> >
> > It would be _really_ nice to be able to see return values from the
> > various gup calls as well.  Is that feasible?
>
> I think it should be feasible. kmem_cache_alloc trace event could show
> return value. I'm supposed gup trace events should be able to do the
> same thing.

Just did a quick test, it is definitely feasible. Please check the below 
test log:

       trace-cmd-200   [000]    99.221486: gup_get_user_pages: 
start=8000000ff0 nr_pages=1 ret=1
       trace-cmd-200   [000]    99.223215: gup_get_user_pages: 
start=8000000fdb nr_pages=1 ret=1
       trace-cmd-200   [000]    99.223298: gup_get_user_pages: 
start=8000000ed0 nr_pages=1 ret=1

nr_pages is the number of pages requested by the gup, ret is the return 
value.

If nobody has objection, I will add it into V3.

Regards,
Yang

> Regards,
> Yang
>
> >

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