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

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Message-ID: <YWT6Ptp/Uo4QGeP4@cmpxchg.org>
Date:   Mon, 11 Oct 2021 23:00:14 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     Michal Hocko <mhocko@...e.com>, Kees Cook <keescook@...omium.org>,
        Pavel Machek <pavel@....cz>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        David Hildenbrand <david@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Colin Cross <ccross@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        Al Viro <viro@...iv.linux.org.uk>,
        Randy Dunlap <rdunlap@...radead.org>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        Peter Xu <peterx@...hat.com>, rppt@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
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        vincenzo.frascino@....com,
        Chinwen Chang (張錦文) 
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        kernel-team <kernel-team@...roid.com>,
        Tim Murray <timmurray@...gle.com>
Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting

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@...gle.com> wrote:
> >
> > On Mon, Oct 11, 2021 at 1:36 AM Michal Hocko <mhocko@...e.com> 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?