linux-kernel - Re: [PATCH] mm: compaction: Trace compaction begin and end

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Date:	Wed, 04 Dec 2013 15:51:57 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH] mm: compaction: Trace compaction begin and end

On 12/04/2013 03:30 PM, Mel Gorman wrote:
> This patch adds two tracepoints for compaction begin and end of a zone. Using
> this it is possible to calculate how much time a workload is spending
> within compaction and potentially debug problems related to cached pfns
> for scanning.

I guess for debugging pfns it would be also useful to print their values 
also in mm_compaction_end.

> In combination with the direct reclaim and slab trace points
> it should be possible to estimate most allocation-related overhead for
> a workload.
>
> Signed-off-by: Mel Gorman <mgorman@...e.de>
> ---
>   include/trace/events/compaction.h | 42 +++++++++++++++++++++++++++++++++++++++
>   mm/compaction.c                   |  4 ++++
>   2 files changed, 46 insertions(+)
>
> diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h
> index fde1b3e..f4e115a 100644
> --- a/include/trace/events/compaction.h
> +++ b/include/trace/events/compaction.h
> @@ -67,6 +67,48 @@ TRACE_EVENT(mm_compaction_migratepages,
>   		__entry->nr_failed)
>   );
>
> +TRACE_EVENT(mm_compaction_begin,
> +	TP_PROTO(unsigned long zone_start, unsigned long migrate_start,
> +		unsigned long zone_end, unsigned long free_start),
> +
> +	TP_ARGS(zone_start, migrate_start, zone_end, free_start),

IMHO a better order would be:
  zone_start, migrate_start, free_start, zone_end
(well especially in the TP_printk part anyway).

> +
> +	TP_STRUCT__entry(
> +		__field(unsigned long, zone_start)
> +		__field(unsigned long, migrate_start)
> +		__field(unsigned long, zone_end)
> +		__field(unsigned long, free_start)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->zone_start = zone_start;
> +		__entry->migrate_start = migrate_start;
> +		__entry->zone_end = zone_end;
> +		__entry->free_start = free_start;
> +	),
> +
> +	TP_printk("zone_start=%lu migrate_start=%lu zone_end=%lu free_start=%lu",
> +		__entry->zone_start,
> +		__entry->migrate_start,
> +		__entry->zone_end,
> +		__entry->free_start)
> +);
> +
> +TRACE_EVENT(mm_compaction_end,
> +	TP_PROTO(int status),
> +
> +	TP_ARGS(status),
> +
> +	TP_STRUCT__entry(
> +		__field(int, status)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->status = status;
> +	),
> +
> +	TP_printk("status=%d", __entry->status)
> +);
>
>   #endif /* _TRACE_COMPACTION_H */
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index c437893..78ff866 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -960,6 +960,8 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
>   	if (compaction_restarting(zone, cc->order) && !current_is_kswapd())
>   		__reset_isolation_suitable(zone);
>
> +	trace_mm_compaction_begin(start_pfn, cc->migrate_pfn, end_pfn, cc->free_pfn);
> +
>   	migrate_prep_local();
>
>   	while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
> @@ -1005,6 +1007,8 @@ out:
>   	cc->nr_freepages -= release_freepages(&cc->freepages);
>   	VM_BUG_ON(cc->nr_freepages != 0);
>
> +	trace_mm_compaction_end(ret);
> +
>   	return ret;
>   }
>
>

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