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

Mel Gorman
2009-08-04T18:12:33Z

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));
__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;
}

--
1.6.3.3