linux-kernel - Re: [PATCH v3] tracing: add 'accounted' entry into output of allocation tracepoints

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Date:   Thu, 19 May 2022 14:35:46 +0300
From:   Vasily Averin <vvs@...nvz.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     YoPOhRctb8wwbmY5@...bon, Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Muchun Song <songmuchun@...edance.com>, kernel@...nvz.org,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v3] tracing: add 'accounted' entry into output of
 allocation tracepoints

On 5/18/22 23:04, Steven Rostedt wrote:
> On Wed, 18 May 2022 09:24:51 +0300
> Vasily Averin <vvs@...nvz.org> wrote:
> 
> FYI, the subject should be something like: mm/tracing:
> Because "tracing:" is reserved for tracing infrastructure updates.

Thank you for noticing.

>> @@ -33,42 +35,46 @@ DECLARE_EVENT_CLASS(kmem_alloc,
>>  		__entry->bytes_req	= bytes_req;
>>  		__entry->bytes_alloc	= bytes_alloc;
>>  		__entry->gfp_flags	= (__force unsigned long)gfp_flags;
>> +		__entry->accounted	= (gfp_flags & __GFP_ACCOUNT) ||
>> +					  (s && s->flags & SLAB_ACCOUNT);
> 
> Now you could make this even faster in the fast path and save just the
> s->flags.
> 
> 	__entry->sflags = s ? s->flags : 0;
> 
>>  	),
>>  
>> -	TP_printk("call_site=%pS ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s",
>> +	TP_printk("call_site=%pS ptr=%p bytes_req=%zu bytes_alloc=%zu gfp_flags=%s accounted=%s",
>>  		(void *)__entry->call_site,
>>  		__entry->ptr,
>>  		__entry->bytes_req,
>>  		__entry->bytes_alloc,
>> -		show_gfp_flags(__entry->gfp_flags))
>> +		show_gfp_flags(__entry->gfp_flags),
>> +		__entry->accounted ? "true" : "false")
> 
> And then have: "accounted=%s":
> 
> 		(__entry->gfp_flags & __GFP_ACCOUNT) ||
> 		(__entry->sflags & SLAB_ACCOUNT) ? "true" : "false"

Unfortunately this returns back sparse warnings about bitwise gfp_t and slab_flags_t casts.
Could you please explain why your variant is faster?

Thank you,
	Vasily Averin