Re: [PATCH] Add slowpath enter/exit trace events

[peter enderborg]

Monitoring both enter/exit for all allocations and track down the one that are slow will be a very
big load on mobile devices or embedded device consuming a lot of battery and cpu. With this we can do useful monitoring
on devices on our field tests with real usage.

On 11/23/2017 01:25 PM, Michal Hocko wrote:
> On Thu 23-11-17 11:43:36, peter.enderborg@xxxxxxxx wrote:
>> From: Peter Enderborg <peter.enderborg@xxxxxxxx>
>>
>> The warning of slow allocation has been removed, this is
>> a other way to fetch that information. But you need
>> to enable the trace. The exit function also returns
>> information about the number of retries, how long
>> it was stalled and failure reason if that happened.
> I think this is just too excessive. We already have a tracepoint for the
> allocation exit. All we need is an entry to have a base to compare with.
> Another usecase would be to measure allocation latency. Information you
> are adding can be (partially) covered by existing tracepoints.
>
>> Signed-off-by: Peter Enderborg <peter.enderborg@xxxxxxxx>
>> ---
>>  include/trace/events/kmem.h | 68 +++++++++++++++++++++++++++++++++++++++++++++
>>  mm/page_alloc.c             | 62 +++++++++++++++++++++++++++++++----------
>>  2 files changed, 116 insertions(+), 14 deletions(-)
>>
>> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
>> index eb57e30..bb882ca 100644
>> --- a/include/trace/events/kmem.h
>> +++ b/include/trace/events/kmem.h
>> @@ -315,6 +315,74 @@ TRACE_EVENT(mm_page_alloc_extfrag,
>>  		__entry->change_ownership)
>>  );
>>  
>> +TRACE_EVENT(mm_page_alloc_slowpath_enter,
>> +
>> +	TP_PROTO(int alloc_order,
>> +		nodemask_t *nodemask,
>> +		gfp_t gfp_flags),
>> +
>> +	TP_ARGS(alloc_order, nodemask, gfp_flags),
>> +
>> +	TP_STRUCT__entry(
>> +		__field(int, alloc_order)
>> +		__field(nodemask_t *, nodemask)
>> +		__field(gfp_t, gfp_flags)
>> +	 ),
>> +
>> +	 TP_fast_assign(
>> +		__entry->alloc_order		= alloc_order;
>> +		__entry->nodemask		= nodemask;
>> +		__entry->gfp_flags		= gfp_flags;
>> +	 ),
>> +
>> +	 TP_printk("alloc_order=%d nodemask=%*pbl gfp_flags=%s",
>> +		__entry->alloc_order,
>> +		nodemask_pr_args(__entry->nodemask),
>> +		show_gfp_flags(__entry->gfp_flags))
>> +);
>> +
>> +TRACE_EVENT(mm_page_alloc_slowpath_exit,
>> +
>> +	TP_PROTO(struct page *page,
>> +		int alloc_order,
>> +		nodemask_t *nodemask,
>> +		u64 alloc_start,
>> +		gfp_t gfp_flags,
>> +		int retrys,
>> +		int exit),
>> +
>> +	TP_ARGS(page, alloc_order, nodemask, alloc_start, gfp_flags,
>> +		retrys, exit),
>> +
>> +	TP_STRUCT__entry(__field(struct page *, page)
>> +		__field(int, alloc_order)
>> +		__field(nodemask_t *, nodemask)
>> +		__field(u64, msdelay)
>> +		__field(gfp_t, gfp_flags)
>> +		__field(int, retrys)
>> +		__field(int, exit)
>> +	),
>> +
>> +	TP_fast_assign(
>> +		__entry->page	     = page;
>> +		__entry->alloc_order = alloc_order;
>> +		__entry->nodemask    = nodemask;
>> +		__entry->msdelay     = jiffies_to_msecs(jiffies-alloc_start);
>> +		__entry->gfp_flags   = gfp_flags;
>> +		__entry->retrys	     = retrys;
>> +		__entry->exit	     = exit;
>> +	),
>> +
>> +	TP_printk("page=%p alloc_order=%d nodemask=%*pbl msdelay=%llu gfp_flags=%s retrys=%d exit=%d",
>> +		__entry->page,
>> +		__entry->alloc_order,
>> +		nodemask_pr_args(__entry->nodemask),
>> +		__entry->msdelay,
>> +		show_gfp_flags(__entry->gfp_flags),
>> +		__entry->retrys,
>> +		__entry->exit)
>> +);
>> +
>>  #endif /* _TRACE_KMEM_H */
>>  
>>  /* This part must be outside protection */
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 48b5b01..bae9cb9 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -104,6 +104,17 @@ DEFINE_PER_CPU(struct work_struct, pcpu_drain);
>>  volatile unsigned long latent_entropy __latent_entropy;
>>  EXPORT_SYMBOL(latent_entropy);
>>  #endif
>> +enum slowpath_exit {
>> +	SLOWPATH_NOZONE = -16,
>> +	SLOWPATH_COMPACT_DEFERRED,
>> +	SLOWPATH_CAN_NOT_DIRECT_RECLAIM,
>> +	SLOWPATH_RECURSION,
>> +	SLOWPATH_NO_RETRY,
>> +	SLOWPATH_COSTLY_ORDER,
>> +	SLOWPATH_OOM_VICTIM,
>> +	SLOWPATH_NO_DIRECT_RECLAIM,
>> +	SLOWPATH_ORDER
>> +};
>>  
>>  /*
>>   * Array of node states.
>> @@ -3908,8 +3919,15 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  	enum compact_result compact_result;
>>  	int compaction_retries;
>>  	int no_progress_loops;
>> +	unsigned long alloc_start = jiffies;
>>  	unsigned int cpuset_mems_cookie;
>>  	int reserve_flags;
>> +	enum slowpath_exit slowpath_exit;
>> +	int retry_count = 0;
>> +
>> +	trace_mm_page_alloc_slowpath_enter(order,
>> +		ac->nodemask,
>> +		gfp_mask);
>>  
>>  	/*
>>  	 * In the slowpath, we sanity check order to avoid ever trying to
>> @@ -3919,7 +3937,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  	 */
>>  	if (order >= MAX_ORDER) {
>>  		WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN));
>> -		return NULL;
>> +		slowpath_exit = SLOWPATH_ORDER;
>> +		goto fail;
>>  	}
>>  
>>  	/*
>> @@ -3951,8 +3970,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  	 */
>>  	ac->preferred_zoneref = first_zones_zonelist(ac->zonelist,
>>  					ac->high_zoneidx, ac->nodemask);
>> -	if (!ac->preferred_zoneref->zone)
>> +	if (!ac->preferred_zoneref->zone) {
>> +		slowpath_exit = SLOWPATH_NOZONE;
>>  		goto nopage;
>> +	}
>>  
>>  	if (gfp_mask & __GFP_KSWAPD_RECLAIM)
>>  		wake_all_kswapds(order, ac);
>> @@ -3998,8 +4019,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  			 * system, so we fail the allocation instead of entering
>>  			 * direct reclaim.
>>  			 */
>> -			if (compact_result == COMPACT_DEFERRED)
>> +			if (compact_result == COMPACT_DEFERRED) {
>> +				slowpath_exit = SLOWPATH_COMPACT_DEFERRED;
>>  				goto nopage;
>> +			}
>>  
>>  			/*
>>  			 * Looks like reclaim/compaction is worth trying, but
>> @@ -4011,6 +4034,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  	}
>>  
>>  retry:
>> +	retry_count++;
>>  	/* Ensure kswapd doesn't accidentally go to sleep as long as we loop */
>>  	if (gfp_mask & __GFP_KSWAPD_RECLAIM)
>>  		wake_all_kswapds(order, ac);
>> @@ -4036,13 +4060,16 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  		goto got_pg;
>>  
>>  	/* Caller is not willing to reclaim, we can't balance anything */
>> -	if (!can_direct_reclaim)
>> +	if (!can_direct_reclaim) {
>> +		slowpath_exit = SLOWPATH_CAN_NOT_DIRECT_RECLAIM;
>>  		goto nopage;
>> +	}
>>  
>>  	/* Avoid recursion of direct reclaim */
>> -	if (current->flags & PF_MEMALLOC)
>> +	if (current->flags & PF_MEMALLOC) {
>> +		slowpath_exit = SLOWPATH_RECURSION;
>>  		goto nopage;
>> -
>> +	}
>>  	/* Try direct reclaim and then allocating */
>>  	page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags, ac,
>>  							&did_some_progress);
>> @@ -4056,16 +4083,18 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  		goto got_pg;
>>  
>>  	/* Do not loop if specifically requested */
>> -	if (gfp_mask & __GFP_NORETRY)
>> +	if (gfp_mask & __GFP_NORETRY) {
>> +		slowpath_exit = SLOWPATH_NO_RETRY;
>>  		goto nopage;
>> -
>> +	}
>>  	/*
>>  	 * Do not retry costly high order allocations unless they are
>>  	 * __GFP_RETRY_MAYFAIL
>>  	 */
>> -	if (costly_order && !(gfp_mask & __GFP_RETRY_MAYFAIL))
>> +	if (costly_order && !(gfp_mask & __GFP_RETRY_MAYFAIL)) {
>> +		slowpath_exit = SLOWPATH_COSTLY_ORDER;
>>  		goto nopage;
>> -
>> +	}
>>  	if (should_reclaim_retry(gfp_mask, order, ac, alloc_flags,
>>  				 did_some_progress > 0, &no_progress_loops))
>>  		goto retry;
>> @@ -4095,9 +4124,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  	/* Avoid allocations with no watermarks from looping endlessly */
>>  	if (tsk_is_oom_victim(current) &&
>>  	    (alloc_flags == ALLOC_OOM ||
>> -	     (gfp_mask & __GFP_NOMEMALLOC)))
>> +	     (gfp_mask & __GFP_NOMEMALLOC))) {
>> +		slowpath_exit = SLOWPATH_OOM_VICTIM;
>>  		goto nopage;
>> -
>> +	}
>>  	/* Retry as long as the OOM killer is making progress */
>>  	if (did_some_progress) {
>>  		no_progress_loops = 0;
>> @@ -4118,9 +4148,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  		 * All existing users of the __GFP_NOFAIL are blockable, so warn
>>  		 * of any new users that actually require GFP_NOWAIT
>>  		 */
>> -		if (WARN_ON_ONCE(!can_direct_reclaim))
>> +		if (WARN_ON_ONCE(!can_direct_reclaim)) {
>> +			slowpath_exit = SLOWPATH_NO_DIRECT_RECLAIM;
>>  			goto fail;
>> -
>> +		}
>>  		/*
>>  		 * PF_MEMALLOC request from this context is rather bizarre
>>  		 * because we cannot reclaim anything and only can loop waiting
>> @@ -4153,6 +4184,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  	warn_alloc(gfp_mask, ac->nodemask,
>>  			"page allocation failure: order:%u", order);
>>  got_pg:
>> +	trace_mm_page_alloc_slowpath_exit(page, order, ac->nodemask,
>> +		alloc_start, gfp_mask, retry_count, slowpath_exit);
>> +
>>  	return page;
>>  }
>>  
>> -- 
>> 2.7.4
>>
>> --
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