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

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Message-ID: <ZFKqh5Dh93UULdse@slm.duckdns.org>
Date:   Wed, 3 May 2023 08:40:07 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Kent Overstreet <kent.overstreet@...ux.dev>,
        Michal Hocko <mhocko@...e.com>,
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        Alexei Starovoitov <ast@...nel.org>,
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Subject: Re: [PATCH 00/40] Memory allocation profiling

On Wed, May 03, 2023 at 08:19:24AM -1000, Tejun Heo wrote:
> > Taking a step back though, given the multitude of allocation sites in
> > the kernel, it's a bit odd that the only accounting we do is the tiny
> > fraction of voluntary vmstat/meminfo reporting. We try to cover the
> > biggest consumers with this of course, but it's always going to be
> > incomplete and is maintenance overhead too. There are on average
> > several gigabytes in unknown memory (total - known vmstats) on our
> > machines. It's difficult to detect regressions easily. And it's per
> > definition the unexpected cornercases that are the trickiest to track
> > down. So it might be doable with BPF, but it does feel like the kernel
> > should do a better job of tracking out of the box and without
> > requiring too much plumbing and somewhat fragile kernel allocation API
> > tracking and probing from userspace.
> 
> 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?

Thanks.

-- 
tejun