On Thu, Feb 28, 2019 at 6:21 PM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>
> On 2/28/19 9:14 AM, 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
> >
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > ---
> > 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)
>
> For node reclaim may_writepage is statically set in node_reclaim_mode,
> so I'm not sure it's worth including it.
>
> > + __field(gfp_t, gfp_flags)
> > + __field(int, zid)
>
> zid seems wasteful and misleading as it's simply derived by
> gfp_zone(gfp_mask), so I would drop it.
>
I agree with you that may_writepage and zid is wasteful, but I found
they are in other tracepoints in this file,
so I place them in this tracepoint as well.
Seems we'd better drop them from other tracepoints as well ?
> > + ),
> > +
> > + 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)
>
> Reporting sc.nr_reclaimed sounds more useful and in line with other
> reclaim tracepoints. Result (sc.nr_reclaimed >= nr_pages) can then be
> derived by postprocessing as the beginning tracepoint contains 'order'
> thus we know nr_pages?
>
Seems reasonable.
Will change it.
> > + ),
> > +
> > + 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)
> >
>
Thanks
Yafang
