Re: [PATCH 00/40] Memory allocation profiling

Michal Hocko
2023-05-07T10:27:35Z

On Thu 04-05-23 08:08:13, Suren Baghdasaryan wrote:
> On Thu, May 4, 2023 at 2:07 AM Michal Hocko <mhocko@suse.com> wrote:
[...]
> > e.g. is it really interesting to know that there is a likely memory
> > leak in seq_file proper doing and allocation? No as it is the specific
> > implementation using seq_file that is leaking most likely. There are
> > other examples like that See?
>
> Yes, I see that. One level tracking does not provide all the
> information needed to track such issues. Something more informative
> would cost more. That's why our proposal is to have a light-weight
> mechanism to get a high level picture and then be able to zoom into a
> specific area using context capture. If you have ideas to improve
> this, I'm open to suggestions.

Well, I think that a more scalable approach would be to not track in
callers but in the allocator itself. The full stack trace might not be
all that important or interesting and maybe even increase the overall
overhead but a partial one with a configurable depth would sound more
interesting to me. A per cache hastable indexed by stack trace reference
and extending slab metadata to store the reference for kfree path won't
be free but the overhead might be just acceptable.

If the stack unwinding is really too expensive for tracking another
option would be to add code tags dynamically to the compiled
kernel without any actual code changes. I can imagine the tracing
infrastructure could be used for that or maybe even consider compiler
plugins to inject code for functions marked as allocators. So the kernel
could be instrumented even without eny userspace tooling required by
users directly.

--
Michal Hocko
SUSE Labs