linux-kernel - Re: [PATCH v4] tracing: add 'accounted' entry into output of allocation tracepoints

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Date:   Mon, 23 May 2022 07:03:36 +0300
From:   Vasily Averin <vvs@...nvz.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, kernel@...nvz.org,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        linux-mm@...ck.org, Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.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>,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v4] tracing: add 'accounted' entry into output of
 allocation tracepoints

On 5/22/22 23:09, Steven Rostedt wrote:
> On Sun, 22 May 2022 07:33:08 +0300
> Vasily Averin <vvs@...nvz.org> wrote:
> 
>>> slab_flags=SLAB_RECLAIM_ACCOUNT|SLAB_ACCOUNT|SLAB_STORE_USER
>>> instead of just printing 'accounted=true/false'. This patch is too
>>> specific to SLAB_ACCOUNT.  
>>
>> Any extra output degrades performance.
>> For my task it's not important to know SLAB flags, I just need to understand,
>> is current allocation accounted or not.
> 
> If you do save the flags in the event, you can report that on output with
> the __print_flags() macro:
> 
>  TP_fast_assign(
> 	[..]
> 	__entry->sflags = s ? s->flags;
> 	[..]
>  )
>  TP_printk("... slab_flags=%s ..",
> 	[..]
> 	__print_flags(sflags, "|",
> 		{ SLAB_CONSISTENCY_CHECKS, "CONSISTENCY_CHECKS" },
> 		{ SLAB_RED_ZONE, "RED_ZONE" },
> 		{ SLAB_POISON, "POISON" },
> 		{ SLAB_HWCACHE_ALIGN, "HWCACHE_ALIGN" },
> 		{ SLAB_CACHE_DMA, "CACHE_DMA" },
> 		{ SLAB_CACHE_DMA32, "CACHE_DMA32" },
> 		{ SLAB_STORE_USER, "STORE_USER" },
> 		{ SLAB_PANIC, "PANIC" }), ... )
> 
> 
> And you get the flag output looking nicely, and all the processing is done
> on the reader path.
> 
> That's if you find it useful at all.

Thank you for explanation!
Yes, we can do it however I really doubt that any other slab flags are of interest to anyone.

Btw. in this form slab flags array causes sparse warnings,
because SLAB_* are defined as bitwise slab_flags_t.
This should be translated to unsigned long similarly to gfp_t flags.

Thank you,
	Vasily Averin