On Tue, Jul 12, 2022 at 9:21 AM Zach O'Keefe <zokeefe@xxxxxxxxxx> wrote:
>
> Hey Yang,
>
> Thanks for taking the time to review this series again.
>
> On Jul 11 14:32, Yang Shi wrote:
> > On Wed, Jul 6, 2022 at 5:06 PM Zach O'Keefe <zokeefe@xxxxxxxxxx> wrote:
> > >
> > > Add a tracepoint to expose mm, address, and enum scan_result of each
> > > hugepage attempted to be collapsed by call to madvise(MADV_COLLAPSE).
> >
> > Is this necessary? Isn't mm_khugepaged_scan_pmd tracepoint good
> > enough? It doesn't have "address", but you should be able to calculate
> > address from it with syscall trace together.
> >
>
> I've also found this useful debugging along the file path. Perhaps the answer to
> that is: add tracepoints to the file path - and we should probably do that - but
> the other issue is that turning on these tracepoints (for the purposes of
> debugging MADV_COLLAPSE) generates a lot of noise from khugepaged that is hard
> to separate out. Augmenting existing tracepoints with .is_khugepaged data
> incurred the risks associated with altering an existing kernel API. WDYT?
Doesn't ftrace show process comm and ID? And I think you also could
trace the specific processes, right?
>
> Thanks again,
> Zach
>
>
> >
> > >
> > > Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
> > > ---
> > > include/trace/events/huge_memory.h | 22 ++++++++++++++++++++++
> > > mm/khugepaged.c | 2 ++
> > > 2 files changed, 24 insertions(+)
> > >
> > > diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
> > > index 55392bf30a03..38d339ffdb16 100644
> > > --- a/include/trace/events/huge_memory.h
> > > +++ b/include/trace/events/huge_memory.h
> > > @@ -167,5 +167,27 @@ TRACE_EVENT(mm_collapse_huge_page_swapin,
> > > __entry->ret)
> > > );
> > >
> > > +TRACE_EVENT(mm_madvise_collapse,
> > > +
> > > + TP_PROTO(struct mm_struct *mm, unsigned long addr, int result),
> > > +
> > > + TP_ARGS(mm, addr, result),
> > > +
> > > + TP_STRUCT__entry(__field(struct mm_struct *, mm)
> > > + __field(unsigned long, addr)
> > > + __field(int, result)
> > > + ),
> > > +
> > > + TP_fast_assign(__entry->mm = mm;
> > > + __entry->addr = addr;
> > > + __entry->result = result;
> > > + ),
> > > +
> > > + TP_printk("mm=%p addr=%#lx result=%s",
> > > + __entry->mm,
> > > + __entry->addr,
> > > + __print_symbolic(__entry->result, SCAN_STATUS))
> > > +);
> > > +
> > > #endif /* __HUGE_MEMORY_H */
> > > #include <trace/define_trace.h>
> > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > > index e0d00180512c..0207fc0a5b2a 100644
> > > --- a/mm/khugepaged.c
> > > +++ b/mm/khugepaged.c
> > > @@ -2438,6 +2438,8 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
> > > if (!mmap_locked)
> > > *prev = NULL; /* Tell caller we dropped mmap_lock */
> > >
> > > + trace_mm_madvise_collapse(mm, addr, result);
> > > +
> > > switch (result) {
> > > case SCAN_SUCCEED:
> > > case SCAN_PMD_MAPPED:
> > > --
> > > 2.37.0.rc0.161.g10f37bed90-goog
> > >
