Re: [PATCH] mm: vmscan: add tracepoints for node reclaim

[Yafang Shao <laoar.shao@gmail.com>]

On Thu, Feb 28, 2019 at 6:17 PM Michal Hocko <mhocko@kernel.org> wrote:
>
> On Thu 28-02-19 16:14:24, Yafang Shao wrote:
> > In the page alloc fast path, it may do node reclaim, which may cause
> > latency spike.
> > We should add tracepoint for this event, and also mesure the latency
> > it causes.
> >
> > So bellow two tracepoints are introduced,
> >       mm_vmscan_node_reclaim_begin
> >       mm_vmscan_node_reclaim_end
>
> This makes some sense to me. Regular direct reclaim already does have
> similar tracepoints. Is there any reason you haven't used
> mm_vmscan_direct_reclaim_{begin,end}_template as all other direct reclaim
> paths?
>

Because I also want to know the node id, which is not show in
mm_vmscan_direct_reclaim_{begin,end}_template.

Or should we modify mm_vmscan_direct_reclaim_{begin,end}_template to
show the node id as well ?

Thanks
Yafang

> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> >  include/trace/events/vmscan.h | 48 +++++++++++++++++++++++++++++++++++++++++++
> >  mm/vmscan.c                   | 13 +++++++++++-
> >  2 files changed, 60 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> > index a1cb913..9310d5b 100644
> > --- a/include/trace/events/vmscan.h
> > +++ b/include/trace/events/vmscan.h
> > @@ -465,6 +465,54 @@
> >               __entry->ratio,
> >               show_reclaim_flags(__entry->reclaim_flags))
> >  );
> > +
> > +TRACE_EVENT(mm_vmscan_node_reclaim_begin,
> > +
> > +     TP_PROTO(int nid, int order, int may_writepage,
> > +             gfp_t gfp_flags, int zid),
> > +
> > +     TP_ARGS(nid, order, may_writepage, gfp_flags, zid),
> > +
> > +     TP_STRUCT__entry(
> > +             __field(int, nid)
> > +             __field(int, order)
> > +             __field(int, may_writepage)
> > +             __field(gfp_t, gfp_flags)
> > +             __field(int, zid)
> > +     ),
> > +
> > +     TP_fast_assign(
> > +             __entry->nid = nid;
> > +             __entry->order = order;
> > +             __entry->may_writepage = may_writepage;
> > +             __entry->gfp_flags = gfp_flags;
> > +             __entry->zid = zid;
> > +     ),
> > +
> > +     TP_printk("nid=%d zid=%d order=%d may_writepage=%d gfp_flags=%s",
> > +             __entry->nid,
> > +             __entry->zid,
> > +             __entry->order,
> > +             __entry->may_writepage,
> > +             show_gfp_flags(__entry->gfp_flags))
> > +);
> > +
> > +TRACE_EVENT(mm_vmscan_node_reclaim_end,
> > +
> > +     TP_PROTO(int result),
> > +
> > +     TP_ARGS(result),
> > +
> > +     TP_STRUCT__entry(
> > +             __field(int, result)
> > +     ),
> > +
> > +     TP_fast_assign(
> > +             __entry->result = result;
> > +     ),
> > +
> > +     TP_printk("result=%d", __entry->result)
> > +);
> >  #endif /* _TRACE_VMSCAN_H */
> >
> >  /* This part must be outside protection */
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index ac4806f..01a0401 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -4240,6 +4240,12 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
> >               .may_swap = 1,
> >               .reclaim_idx = gfp_zone(gfp_mask),
> >       };
> > +     int result;
> > +
> > +     trace_mm_vmscan_node_reclaim_begin(pgdat->node_id, order,
> > +                                     sc.may_writepage,
> > +                                     sc.gfp_mask,
> > +                                     sc.reclaim_idx);
> >
> >       cond_resched();
> >       fs_reclaim_acquire(sc.gfp_mask);
> > @@ -4267,7 +4273,12 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
> >       current->flags &= ~PF_SWAPWRITE;
> >       memalloc_noreclaim_restore(noreclaim_flag);
> >       fs_reclaim_release(sc.gfp_mask);
> > -     return sc.nr_reclaimed >= nr_pages;
> > +
> > +     result = sc.nr_reclaimed >= nr_pages;
> > +
> > +     trace_mm_vmscan_node_reclaim_end(result);
> > +
> > +     return result;
> >  }
> >
> >  int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
> > --
> > 1.8.3.1
>
> --
> Michal Hocko
> SUSE Labs