linux-kernel - Re: [PATCH 00/40] Memory allocation profiling

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Message-ID: <CAJuCfpEPkCJZO2svT-GfmpJ+V-jSLyFDKM_atnqPVRBKtzgtnQ@mail.gmail.com>
Date:   Wed, 3 May 2023 12:41:08 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Kent Overstreet <kent.overstreet@...ux.dev>,
        Johannes Weiner <hannes@...xchg.org>,
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Subject: Re: [PATCH 00/40] Memory allocation profiling

On Wed, May 3, 2023 at 12:09 PM Tejun Heo <tj@...nel.org> wrote:
>
> On Wed, May 03, 2023 at 08:58:51AM -1000, Tejun Heo wrote:
> > On Wed, May 03, 2023 at 02:56:44PM -0400, Kent Overstreet wrote:
> > > On Wed, May 03, 2023 at 08:40:07AM -1000, Tejun Heo wrote:
> > > > > Yeah, easy / default visibility argument does make sense to me.
> > > >
> > > > So, a bit of addition here. If this is the thrust, the debugfs part seems
> > > > rather redundant, right? That's trivially obtainable with tracing / bpf and
> > > > in a more flexible and performant manner. Also, are we happy with recording
> > > > just single depth for persistent tracking?

IIUC, by single depth you mean no call stack capturing?
If so, that's the idea behind the context capture feature so that we
can enable it on specific allocations only after we determine there is
something interesting there. So, with low-cost persistent tracking we
can determine the suspects and then pay some more to investigate those
suspects in more detail.

> > >
> > > Not sure what you're envisioning?
> > >
> > > I'd consider the debugfs interface pretty integral; it's much more
> > > discoverable for users, and it's hardly any code out of the whole
> > > patchset.
> >
> > You can do the same thing with a bpftrace one liner tho. That's rather
> > difficult to beat.

debugfs seemed like a natural choice for such information. If another
interface is more appropriate I'm happy to explore that.

>
> Ah, shit, I'm an idiot. Sorry. I thought allocations was under /proc and
> allocations.ctx under debugfs. I meant allocations.ctx is redundant.

Do you mean that we could display allocation context in
debugfs/allocations file (for the allocations which we explicitly
enabled context capturing)?

>
> Thanks.
>
> --
> tejun