Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting

[Suren Baghdasaryan]

On Mon, Oct 11, 2021 at 8:00 PM Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
>
> On Mon, Oct 11, 2021 at 06:20:25PM -0700, Suren Baghdasaryan wrote:
> > On Mon, Oct 11, 2021 at 6:18 PM Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:
> > >
> > > On Mon, Oct 11, 2021 at 1:36 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
> > > >
> > > > On Fri 08-10-21 13:58:01, Kees Cook wrote:
> > > > > - Strings for "anon" specifically have no required format (this is good)
> > > > >   it's informational like the task_struct::comm and can (roughly)
> > > > >   anything. There's no naming convention for memfds, AF_UNIX, etc. Why
> > > > >   is one needed here? That seems like a completely unreasonable
> > > > >   requirement.
> > > >
> > > > I might be misreading the justification for the feature. Patch 2 is
> > > > talking about tools that need to understand memeory usage to make
> > > > further actions. Also Suren was suggesting "numbering convetion" as an
> > > > argument against.
> > > >
> > > > So can we get a clear example how is this being used actually? If this
> > > > is just to be used to debug by humans than I can see an argument for
> > > > human readable form. If this is, however, meant to be used by tools to
> > > > make some actions then the argument for strings is much weaker.
> > >
> > > The simplest usecase is when we notice that a process consumes more
> > > memory than usual and we do "cat /proc/$(pidof my_process)/maps" to
> > > check which area is contributing to this growth. The names we assign
> > > to anonymous areas are descriptive enough for a developer to get an
> > > idea where the increased consumption is coming from and how to proceed
> > > with their investigation.
> > > There are of course cases when tools are involved, but the end-user is
> > > always a human and the final report should contain easily
> > > understandable data.
> > >
> > > IIUC, the main argument here is whether the userspace can provide
> > > tools to perform the translations between ids and names, with the
> > > kernel accepting and reporting ids instead of strings. Technically
> > > it's possible, but to be practical that conversion should be fast
> > > because we will need to make name->id conversion potentially for each
> > > mmap. On the consumer side the performance is not as critical, but the
> > > fact that instead of dumping /proc/$pid/maps we will have to parse the
> > > file, do id->name conversion and replace all [anon:id] with
> > > [anon:name] would be an issue when we do that in bulk, for example
> > > when collecting system-wide data for a bugreport.
>
> Is that something you need to do client-side? Or could the bug tool
> upload the userspace-maintained name:ids database alongside the
> /proc/pid/maps dump for external processing?

You can generate a bugreport and analyze it locally or submit it as an
attachment to a bug for further analyzes.
Sure, we can attach the id->name conversion table to the bugreport but
either way, some tool would have to post-process it to resolve the
ids. If we are not analyzing the results immediately then that step
can be postponed and I think that's what you mean? If so, then yes,
that is correct.