Re: [PATCH 2/3] mm/compaction: add more trace to understand compaction start/finish condition

[Vlastimil Babka]

On 12/03/2014 08:52 AM, Joonsoo Kim wrote:
> It is not well analyzed that when compaction start and when compaction
> finish. With this tracepoint for compaction start/finish condition, I can
> find following bug.
> 
> http://www.spinics.net/lists/linux-mm/msg81582.html
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> ---
>  include/linux/compaction.h        |    2 +
>  include/trace/events/compaction.h |   91 +++++++++++++++++++++++++++++++++++++
>  mm/compaction.c                   |   40 ++++++++++++++--
>  3 files changed, 129 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index a9547b6..bdb4b99 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -12,6 +12,8 @@
>  #define COMPACT_PARTIAL		3
>  /* The full zone was compacted */
>  #define COMPACT_COMPLETE	4
> +/* For more detailed tracepoint output, will be converted to COMPACT_CONTINUE */
> +#define COMPACT_NOT_SUITABLE	5

So this makes it sound like the value means "compaction was not suitable to do
in this zone", but later it means something different.

>  /* When adding new state, please change compaction_status_string, too */
>  
>  /* Used to signal whether compaction detected need_sched() or lock contention */
> diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h
> index 139020b..5e47cb2 100644
> --- a/include/trace/events/compaction.h
> +++ b/include/trace/events/compaction.h
> @@ -164,6 +164,97 @@ TRACE_EVENT(mm_compaction_end,
>  		compaction_status_string[__entry->status])
>  );
>  
> +TRACE_EVENT(mm_compaction_try_to_compact_pages,
> +
> +	TP_PROTO(
> +		unsigned int order,
> +		gfp_t gfp_mask,
> +		enum migrate_mode mode,
> +		int alloc_flags,
> +		int classzone_idx),
> +
> +	TP_ARGS(order, gfp_mask, mode, alloc_flags, classzone_idx),
> +
> +	TP_STRUCT__entry(
> +		__field(unsigned int, order)
> +		__field(gfp_t, gfp_mask)
> +		__field(enum migrate_mode, mode)
> +		__field(int, alloc_flags)
> +		__field(int, classzone_idx)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->order = order;
> +		__entry->gfp_mask = gfp_mask;
> +		__entry->mode = mode;
> +		__entry->alloc_flags = alloc_flags;
> +		__entry->classzone_idx = classzone_idx;
> +	),
> +
> +	TP_printk("order=%u gfp_mask=0x%x mode=%d alloc_flags=0x%x classzone_idx=%d",
> +		__entry->order,
> +		__entry->gfp_mask,
> +		(int)__entry->mode,
> +		__entry->alloc_flags,
> +		__entry->classzone_idx)
> +);
> +
> +DECLARE_EVENT_CLASS(mm_compaction_suitable_template,
> +
> +	TP_PROTO(struct zone *zone,
> +		unsigned int order,
> +		int alloc_flags,
> +		int classzone_idx,
> +		int ret),
> +
> +	TP_ARGS(zone, order, alloc_flags, classzone_idx, ret),
> +
> +	TP_STRUCT__entry(
> +		__field(char *, name)
> +		__field(unsigned int, order)
> +		__field(int, alloc_flags)
> +		__field(int, classzone_idx)
> +		__field(int, ret)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->name = (char *)zone->name;

This does not identify the NUMA node, just the zone type, isn't it?

> +		__entry->order = order;
> +		__entry->alloc_flags = alloc_flags;
> +		__entry->classzone_idx = classzone_idx;
> +		__entry->ret = ret;
> +	),
> +
> +	TP_printk("zone=%-8s order=%u alloc_flags=0x%x classzone_idx=%d ret=%s",
> +		__entry->name,
> +		__entry->order,
> +		__entry->alloc_flags,
> +		__entry->classzone_idx,
> +		compaction_status_string[__entry->ret])
> +);
> +
> +DEFINE_EVENT(mm_compaction_suitable_template, mm_compaction_finished,
> +
> +	TP_PROTO(struct zone *zone,
> +		unsigned int order,
> +		int alloc_flags,
> +		int classzone_idx,
> +		int ret),
> +
> +	TP_ARGS(zone, order, alloc_flags, classzone_idx, ret)
> +);
> +
> +DEFINE_EVENT(mm_compaction_suitable_template, mm_compaction_suitable,
> +
> +	TP_PROTO(struct zone *zone,
> +		unsigned int order,
> +		int alloc_flags,
> +		int classzone_idx,
> +		int ret),
> +
> +	TP_ARGS(zone, order, alloc_flags, classzone_idx, ret)
> +);
> +
>  #endif /* _TRACE_COMPACTION_H */
>  
>  /* This part must be outside protection */
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 4c7b837..f5d2405 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -25,6 +25,7 @@ char *compaction_status_string[] = {
>  	"continue",
>  	"partial",
>  	"complete",
> +	"not_suitable_page",

So here COMPACT_NOT_SUITABLE is interpreted as "no suitable page was found".

>  };
>  
>  static inline void count_compact_event(enum vm_event_item item)
> @@ -1048,7 +1049,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
>  	return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
>  }
>  
> -static int compact_finished(struct zone *zone, struct compact_control *cc,
> +static int __compact_finished(struct zone *zone, struct compact_control *cc,
>  			    const int migratetype)
>  {
>  	unsigned int order;
> @@ -1103,7 +1104,21 @@ static int compact_finished(struct zone *zone, struct compact_control *cc,
>  			return COMPACT_PARTIAL;
>  	}
>  
> -	return COMPACT_CONTINUE;
> +	return COMPACT_NOT_SUITABLE;

So for compact_finished tracepoint you print "not_suitable_page" and it's what
it really means - watermarks were met, but no suitable page was actually found.
But you use "COMPACT_NOT_SUITABLE" which hints at a different meaning.

> +}
> +
> +static int compact_finished(struct zone *zone, struct compact_control *cc,
> +			    const int migratetype)
> +{
> +	int ret;
> +
> +	ret = __compact_finished(zone, cc, migratetype);
> +	trace_mm_compaction_finished(zone, cc->order, cc->alloc_flags,
> +						cc->classzone_idx, ret);
> +	if (ret == COMPACT_NOT_SUITABLE)
> +		ret = COMPACT_CONTINUE;
> +
> +	return ret;
>  }
>  
>  /*
> @@ -1113,7 +1128,7 @@ static int compact_finished(struct zone *zone, struct compact_control *cc,
>   *   COMPACT_PARTIAL  - If the allocation would succeed without compaction
>   *   COMPACT_CONTINUE - If compaction should run now
>   */
> -unsigned long compaction_suitable(struct zone *zone, int order,
> +static unsigned long __compaction_suitable(struct zone *zone, int order,
>  					int alloc_flags, int classzone_idx)
>  {
>  	int fragindex;
> @@ -1157,11 +1172,25 @@ unsigned long compaction_suitable(struct zone *zone, int order,
>  	 */
>  	fragindex = fragmentation_index(zone, order);
>  	if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
> -		return COMPACT_SKIPPED;
> +		return COMPACT_NOT_SUITABLE;

But here in compaction_suitable, return here means that fragmentation seems to
be low and it's unlikely that compaction will help. COMPACT_NOT_SUITABLE sounds
like a good name, but then tracepoint prints "not_suitable_page" and that's
something different.

>  	return COMPACT_CONTINUE;
>  }
>  
> +unsigned long compaction_suitable(struct zone *zone, int order,
> +					int alloc_flags, int classzone_idx)
> +{
> +	unsigned long ret;
> +
> +	ret = __compaction_suitable(zone, order, alloc_flags, classzone_idx);
> +	trace_mm_compaction_suitable(zone, order, alloc_flags,
> +						classzone_idx, ret);
> +	if (ret == COMPACT_NOT_SUITABLE)
> +		ret = COMPACT_SKIPPED;

I don't like this wrapping just for tracepints, but I don't know of a better way :/

> +
> +	return ret;
> +}
> +
>  static int compact_zone(struct zone *zone, struct compact_control *cc)
>  {
>  	int ret;
> @@ -1375,6 +1404,9 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
>  	if (!order || !may_enter_fs || !may_perform_io)
>  		return COMPACT_SKIPPED;
>  
> +	trace_mm_compaction_try_to_compact_pages(order, gfp_mask, mode,
> +					alloc_flags, classzone_idx);
> +
>  	/* Compact each zone in the list */
>  	for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
>  								nodemask) {
> 

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