linux-kernel - Re: [PATCH v2] mm: emit tracepoint when RSS changes by threshold

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Message-ID: <20190905144310.GA14491@dhcp22.suse.cz>
Date:   Thu, 5 Sep 2019 16:43:10 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Tim Murray <timmurray@...gle.com>,
        carmenjackson@...gle.com, mayankgupta@...gle.com,
        dancol@...gle.com, rostedt@...dmis.org, minchan@...nel.org,
        akpm@...ux-foundation.org, kernel-team@...roid.com,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jerome Glisse <jglisse@...hat.com>, linux-mm@...ck.org,
        Matthew Wilcox <willy@...radead.org>,
        Ralph Campbell <rcampbell@...dia.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v2] mm: emit tracepoint when RSS changes by threshold

[Add Steven]

On Wed 04-09-19 12:28:08, Joel Fernandes wrote:
> On Wed, Sep 4, 2019 at 11:38 AM Michal Hocko <mhocko@...nel.org> wrote:
> >
> > On Wed 04-09-19 11:32:58, Joel Fernandes wrote:
[...]
> > > but also for reducing
> > > tracing noise. Flooding the traces makes it less useful for long traces and
> > > post-processing of traces. IOW, the overhead reduction is a bonus.
> >
> > This is not really anything special for this tracepoint though.
> > Basically any tracepoint in a hot path is in the same situation and I do
> > not see a point why each of them should really invent its own way to
> > throttle. Maybe there is some way to do that in the tracing subsystem
> > directly.
> 
> I am not sure if there is a way to do this easily. Add to that, the fact that
> you still have to call into trace events. Why call into it at all, if you can
> filter in advance and have a sane filtering default?
> 
> The bigger improvement with the threshold is the number of trace records are
> almost halved by using a threshold. The number of records went from 4.6K to
> 2.6K.

Steven, would it be feasible to add a generic tracepoint throttling?
-- 
Michal Hocko
SUSE Labs