Date:   Mon, 11 Oct 2021 22:36:24 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Johannes Weiner <hannes@...xchg.org>
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>,
        Catalin Marinas <catalin.marinas@....com>,
        vincenzo.frascino@....com,
        Chinwen Chang (張錦文) 
        <chinwen.chang@...iatek.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jann Horn <jannh@...gle.com>, apopple@...dia.com,
        Yu Zhao <yuzhao@...gle.com>, Will Deacon <will@...nel.org>,
        fenghua.yu@...el.com, thunder.leizhen@...wei.com,
        Hugh Dickins <hughd@...gle.com>, feng.tang@...el.com,
        Jason Gunthorpe <jgg@...pe.ca>, Roman Gushchin <guro@...com>,
        Thomas Gleixner <tglx@...utronix.de>, krisman@...labora.com,
        Chris Hyser <chris.hyser@...cle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Jens Axboe <axboe@...nel.dk>, legion@...nel.org,
        Rolf Eike Beer <eb@...ix.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Muchun Song <songmuchun@...edance.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Thomas Cedeno <thomascedeno@...gle.com>, sashal@...nel.org,
        cxfcosmos@...il.com, LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-mm <linux-mm@...ck.org>,
        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 8:00 PM Johannes Weiner <hannes@...xchg.org> 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@...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?

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.

Powered by blists - more mailing lists