linux-kernel - Re: [PATCH v2 2/2] mm, slab: Show last shrink time in us when slab/shrink is read

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Message-ID: <20190719142906.GU30461@dhcp22.suse.cz>
Date:   Fri, 19 Jul 2019 16:29:06 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>
Subject: Re: [PATCH v2 2/2] mm, slab: Show last shrink time in us when
 slab/shrink is read

On Fri 19-07-19 10:07:20, Waiman Long wrote:
> On 7/19/19 2:14 AM, Michal Hocko wrote:
> > On Wed 17-07-19 16:24:13, Waiman Long wrote:
> >> The show method of /sys/kernel/slab/<slab>/shrink sysfs file currently
> >> returns nothing. This is now modified to show the time of the last
> >> cache shrink operation in us.
> > Isn't this something that tracing can be used for without any kernel
> > modifications?
> 
> That is true, but it will be a bit more cumbersome to get the data.

I have no say for this code but if there is a way to capture timing data
I prefer to rely on the tracing infrastructure. If the current tooling
makes it cumbersome to get then this is a good reason to ask for a less
cumbersome way. On the other hand, if you somehow hardwire it to a user
visible interface then you just establish ABI which might stand in way
for potential/future development.

So take it as my 2c
-- 
Michal Hocko
SUSE Labs