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

KOSAKI Motohiro
2009-08-05T09:24:46Z

> 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?

> __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?