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

From: Vasily Averin <vvs@openvz.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	kernel@openvz.org, linux-kernel@vger.kernel.org,
	Ingo Molnar <mingo@redhat.com>,
	linux-mm@kvack.org, Shakeel Butt <shakeelb@google.com>,
	Roman Gushchin <roman.gushchin@linux.dev>,
	Vlastimil Babka <vbabka@suse.cz>,
	Matthew Wilcox <willy@infradead.org>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	David Rientjes <rientjes@google.com>,
	Pekka Enberg <penberg@kernel.org>,
	Christoph Lameter <cl@linux.com>, Michal Hocko <mhocko@suse.com>,
	Muchun Song <songmuchun@bytedance.com>
Subject: Re: [PATCH v4] tracing: add 'accounted' entry into output of allocation tracepoints
Date: Mon, 23 May 2022 07:03:36 +0300	[thread overview]
Message-ID: <100d8ba9-80e4-4ba8-0568-a77f0dbd4f78@openvz.org> (raw)
In-Reply-To: <20220522160943.5e5950e0@gandalf.local.home>

On 5/22/22 23:09, Steven Rostedt wrote:
> On Sun, 22 May 2022 07:33:08 +0300
> Vasily Averin <vvs@openvz.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