Re: [PATCH 3/4] tracing, page-allocator: Add trace event for page traffic related to the buddy lists

Mel Gorman
2009-08-05T09:43:49Z

On Wed, Aug 05, 2009 at 06:24:40PM +0900, KOSAKI Motohiro wrote:
> > The page allocation trace event reports that a page was successfully allocated
> > but it does not specify where it came from. When analysing performance,
> > it can be important to distinguish between pages coming from the per-cpu
> > allocator and pages coming from the buddy lists as the latter requires the
> > zone lock to the taken and more data structures to be examined.
> >
> > This patch adds a trace event for __rmqueue reporting when a page is being
> > allocated from the buddy lists. It distinguishes between being called
> > to refill the per-cpu lists or whether it is a high-order allocation.
> > Similarly, this patch adds an event to catch when the PCP lists are being
> > drained a little and pages are going back to the buddy lists.
> >
> > This is trickier to draw conclusions from but high activity on those
> > events could explain why there were a large number of cache misses on a
> > page-allocator-intensive workload. The coalescing and splitting of buddies
> > involves a lot of writing of page metadata and cache line bounces not to
> > mention the acquisition of an interrupt-safe lock necessary to enter this
> > path.
> >
> > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> > Acked-by: Rik van Riel <riel@redhat.com>
> > ---
> > include/trace/events/kmem.h | 54 +++++++++++++++++++++++++++++++++++++++++++
> > mm/page_alloc.c | 2 +
> > 2 files changed, 56 insertions(+), 0 deletions(-)
> >
> > diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> > index 0b4002e..3be3df3 100644
> > --- a/include/trace/events/kmem.h
> > +++ b/include/trace/events/kmem.h
> > @@ -311,6 +311,60 @@ TRACE_EVENT(mm_page_alloc,
> > show_gfp_flags(__entry->gfp_flags))
> > );
> >
> > +TRACE_EVENT(mm_page_alloc_zone_locked,
> > +
> > + TP_PROTO(const void *page, unsigned int order,
> > + int migratetype, int percpu_refill),
> > +
> > + TP_ARGS(page, order, migratetype, percpu_refill),
> > +
> > + TP_STRUCT__entry(
> > + __field( const void *, page )
> > + __field( unsigned int, order )
> > + __field( int, migratetype )
> > + __field( int, percpu_refill )
> > + ),
> > +
> > + TP_fast_assign(
> > + __entry->page = page;
> > + __entry->order = order;
> > + __entry->migratetype = migratetype;
> > + __entry->percpu_refill = percpu_refill;
> > + ),
> > +
> > + TP_printk("page=%p pfn=%lu order=%u migratetype=%d percpu_refill=%d",
> > + __entry->page,
> > + page_to_pfn((struct page *)__entry->page),
> > + __entry->order,
> > + __entry->migratetype,
> > + __entry->percpu_refill)
> > +);
> > +
> > +TRACE_EVENT(mm_page_pcpu_drain,
> > +
> > + TP_PROTO(const void *page, int order, int migratetype),
> > +
> > + TP_ARGS(page, order, migratetype),
> > +
> > + TP_STRUCT__entry(
> > + __field( const void *, page )
> > + __field( int, order )
> > + __field( int, migratetype )
> > + ),
> > +
> > + TP_fast_assign(
> > + __entry->page = page;
> > + __entry->order = order;
> > + __entry->migratetype = migratetype;
> > + ),
> > +
> > + TP_printk("page=%p pfn=%lu order=%d migratetype=%d",
> > + __entry->page,
> > + page_to_pfn((struct page *)__entry->page),
> > + __entry->order,
> > + __entry->migratetype)
> > +);
> > +
> > TRACE_EVENT(mm_page_alloc_extfrag,
> >
> > TP_PROTO(const void *page,
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index c2c90cd..35b92a9 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -535,6 +535,7 @@ static void free_pages_bulk(struct zone *zone, int count,
> > page = list_entry(list->prev, struct page, lru);
> > /* have to delete it as __free_one_page list manipulates */
> > list_del(&page->lru);
> > + trace_mm_page_pcpu_drain(page, order, page_private(page));
>
> pcp refill (trace_mm_page_alloc_zone_locked) logged migratetype, but
> this tracepoint doesn't. why?
>

It does log migratetype as migratetype is in page_private(page) in this
context.

>
> > __free_one_page(page, zone, order, page_private(page));
> > }
> > spin_unlock(&zone->lock);
> > @@ -878,6 +879,7 @@ retry_reserve:
> > }
> > }
> >
> > + trace_mm_page_alloc_zone_locked(page, order, migratetype, order == 0);
> > return page;
> > }
>
> Umm, Can we assume order-0 always mean pcp refill?
>

Right now, that assumption is accurate. Which callpath ends up here with
order == 0 and it's not a PCP refill?

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab