linux-kernel - Re: [PATCH 1/3] Add a new field to struct shrinker

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Date:	Thu, 11 Aug 2016 20:09:25 -0700
From:	Tony Jones <tonyj@...e.de>
To:	Mel Gorman <mgorman@...hsingularity.net>,
	Dave Chinner <david@...morbit.com>
Cc:	Janani Ravichandran <janani.rvchndrn@...il.com>,
	Rik van Riel <riel@...riel.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] Add a new field to struct shrinker

On 07/29/2016 06:00 AM, Mel Gorman wrote:
> On Fri, Jul 29, 2016 at 10:13:40AM +1000, Dave Chinner wrote:
>> On Thu, Jul 28, 2016 at 11:25:13AM +0100, Mel Gorman wrote:
>>> On Thu, Jul 28, 2016 at 03:49:47PM +1000, Dave Chinner wrote:
>>>> Seems you're all missing the obvious.
>>>>
>>>> Add a tracepoint for a shrinker callback that includes a "name"
>>>> field, have the shrinker callback fill it out appropriately. e.g
>>>> in the superblock shrinker:
>>>>
>>>> 	trace_shrinker_callback(shrinker, shrink_control, sb->s_type->name);
>>>>
>>>
>>> That misses capturing the latency of the call unless there is a begin/end
>>> tracepoint.
>>
>> Sure, but I didn't see that in the email talking about how to add a
>> name. Even if it is a requirement, it's not necessary as we've
>> already got shrinker runtime measurements from the
>> trace_mm_shrink_slab_start and trace_mm_shrink_slab_end trace
>> points. With the above callback event, shrinker call runtime is
>> simply the time between the calls to the same shrinker within
>> mm_shrink_slab start/end trace points.
>>
> 
> Fair point. It's not that hard to correlate them.

True but the scan_objects callback is only called if we have >batch_size objects.

It's possible to accumulate quite some time without calling the callback and being able to obtain 
the s_type->name.   So this time all gets associated with just super_cache_scan.