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

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Message-ID: <CAKOZueuGML_ZX8Pk5csLK7TWEVwqGj=KZTh2TELNsLytkrHCTQ@mail.gmail.com>
Date:   Wed, 4 Sep 2019 10:17:33 -0700
From:   Daniel Colascione <dancol@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Tim Murray <timmurray@...gle.com>,
        Carmen Jackson <carmenjackson@...gle.com>,
        Mayank Gupta <mayankgupta@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Android Kernel Team <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 <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

On Wed, Sep 4, 2019 at 8:38 AM Michal Hocko <mhocko@...nel.org> 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 agree. I'd rather not special-case RSS in this way, especially not
with a hardcoded aggregation and thresholding configuration. It should
be possible to handle high-frequency trace data point aggregation in a
general way. Why shouldn't we be able to get a time series for, say,
dirty pages? Or various slab counts? IMHO, any counter on the system
ought to be observable in a uniform way.