On Wed, 27 Jul 2016 10:47:59 -0400
Janani Ravichandran <janani.rvchndrn@xxxxxxxxx> wrote:
> Add tracepoints to the slowpath code to gather some information.
> The tracepoints can also be used to find out how much time was spent in
> the slowpath.
>
> Signed-off-by: Janani Ravichandran <janani.rvchndrn@xxxxxxxxx>
> ---
> include/trace/events/kmem.h | 40 ++++++++++++++++++++++++++++++++++++++++
> mm/page_alloc.c | 5 +++++
> 2 files changed, 45 insertions(+)
>
> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> index 6b2e154..c19ab9f 100644
> --- a/include/trace/events/kmem.h
> +++ b/include/trace/events/kmem.h
> @@ -169,6 +169,46 @@ TRACE_EVENT(mm_page_free,
> __entry->order)
> );
>
> +TRACE_EVENT(mm_slowpath_begin,
> +
> + TP_PROTO(gfp_t gfp_mask, int order),
> +
> + TP_ARGS(gfp_mask, order),
> +
> + TP_STRUCT__entry(
> + __field(gfp_t, gfp_mask)
> + __field(int, order)
> + ),
> +
> + TP_fast_assign(
> + __entry->gfp_mask = gfp_mask;
> + __entry->order = order;
> + ),
> +
> + TP_printk("gfp_mask:%s order=%d",
> + show_gfp_flags(__entry->gfp_mask),
> + __entry->order)
> +);
> +
> +TRACE_EVENT(mm_slowpath_end,
> +
> + TP_PROTO(struct page *page),
> +
> + TP_ARGS(page),
> +
> + TP_STRUCT__entry(
> + __field(unsigned long, pfn)
> + ),
> +
> + TP_fast_assign(
> + __entry->pfn = page ? page_to_pfn(page) : -1UL;
> + ),
> +
> + TP_printk("page=%p pfn=%lu",
> + __entry->pfn != -1UL ? pfn_to_page(__entry->pfn) : NULL,
Note, userspace tools will not be able to do this conversion (like
trace-cmd or perf).
> + __entry->pfn != -1UL ? __entry->pfn : 0)
> +);
> +
> TRACE_EVENT(mm_page_free_batched,
>
> TP_PROTO(struct page *page, int cold),
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8b3e134..be9c688 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3595,6 +3595,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)))
> gfp_mask &= ~__GFP_ATOMIC;
>
> + trace_mm_slowpath_begin(gfp_mask, order);
> +
> retry:
> if (gfp_mask & __GFP_KSWAPD_RECLAIM)
> wake_all_kswapds(order, ac);
> @@ -3769,6 +3771,9 @@ noretry:
> nopage:
> warn_alloc_failed(gfp_mask, order, NULL);
> got_pg:
> +
> + trace_mm_slowpath_end(page);
> +
I'm thinking you only need one tracepoint, and use function_graph
tracer for the length of the function call.
# cd /sys/kernel/debug/tracing
# echo __alloc_pages_nodemask > set_ftrace_filter
# echo function_graph > current_tracer
# echo 1 > events/kmem/trace_mm_slowpath/enable
-- Steve
> return page;
> }
>
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