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    Subject[PATCH 3/6] tracing, page-allocator: Add trace event for page traffic related to the buddy lists
    Date
    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 | 51 +++++++++++++++++++++++++++++++++++++++++++
    mm/page_alloc.c | 2 +
    2 files changed, 53 insertions(+), 0 deletions(-)

    diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
    index aae16ee..eaf46bd 100644
    --- a/include/trace/events/kmem.h
    +++ b/include/trace/events/kmem.h
    @@ -299,6 +299,57 @@ TRACE_EVENT(mm_page_alloc,
    show_gfp_flags(__entry->gfp_flags))
    );

    +TRACE_EVENT(mm_page_alloc_zone_locked,
    +
    + TP_PROTO(struct page *page, unsigned int order, int migratetype),
    +
    + TP_ARGS(page, order, migratetype),
    +
    + TP_STRUCT__entry(
    + __field( struct page *, page )
    + __field( unsigned int, order )
    + __field( int, migratetype )
    + ),
    +
    + TP_fast_assign(
    + __entry->page = page;
    + __entry->order = order;
    + __entry->migratetype = migratetype;
    + ),
    +
    + TP_printk("page=%p pfn=%lu order=%u migratetype=%d percpu_refill=%d",
    + __entry->page,
    + page_to_pfn(__entry->page),
    + __entry->order,
    + __entry->migratetype,
    + __entry->order == 0)
    +);
    +
    +TRACE_EVENT(mm_page_pcpu_drain,
    +
    + TP_PROTO(struct page *page, int order, int migratetype),
    +
    + TP_ARGS(page, order, migratetype),
    +
    + TP_STRUCT__entry(
    + __field( struct page *, 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(__entry->page),
    + __entry->order,
    + __entry->migratetype)
    +);
    +
    TRACE_EVENT(mm_page_alloc_extfrag,

    TP_PROTO(struct page *page,
    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index 4c20bfa..bbd7de8 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);
    @@ -876,6 +877,7 @@ retry_reserve:
    }
    }

    + trace_mm_page_alloc_zone_locked(page, order, migratetype);
    return page;
    }

    --
    1.6.3.3


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