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

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Date:   Thu, 7 Oct 2021 08:45:21 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     David Hildenbrand <david@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Pavel Machek <pavel@....cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Colin Cross <ccross@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        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,
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        Thomas Gleixner <tglx@...utronix.de>, krisman@...labora.com,
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        Jens Axboe <axboe@...nel.dk>, legion@...nel.org,
        Rolf Eike Beer <eb@...ix.com>,
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        linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-mm <linux-mm@...ck.org>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting

On Thu, Oct 7, 2021 at 12:59 AM Michal Hocko <mhocko@...e.com> wrote:
>
> On Wed 06-10-21 08:01:56, Suren Baghdasaryan wrote:
> > On Wed, Oct 6, 2021 at 2:27 AM David Hildenbrand <david@...hat.com> wrote:
> > >
> > > On 06.10.21 10:27, Michal Hocko wrote:
> > > > On Tue 05-10-21 23:57:36, John Hubbard wrote:
> > > > [...]
> > > >> 1) Yes, just leave the strings in the kernel, that's simple and
> > > >> it works, and the alternatives don't really help your case nearly
> > > >> enough.
> > > >
> > > > I do not have a strong opinion. Strings are easier to use but they
> > > > are more involved and the necessity of kref approach just underlines
> > > > that. There are going to be new allocations and that always can lead
> > > > to surprising side effects.  These are small (80B at maximum) so the
> > > > overall footpring shouldn't all that large by default but it can grow
> > > > quite large with a very high max_map_count. There are workloads which
> > > > really require the default to be set high (e.g. heavy mremap users). So
> > > > if anything all those should be __GFP_ACCOUNT and memcg accounted.
> > > >
> > > > I do agree that numbers are just much more simpler from accounting,
> > > > performance and implementation POV.
> > >
> > > +1
> > >
> > > I can understand that having a string can be quite beneficial e.g., when
> > > dumping mmaps. If only user space knows the id <-> string mapping, that
> > > can be quite tricky.
> > >
> > > However, I also do wonder if there would be a way to standardize/reserve
> > > ids, such that a given id always corresponds to a specific user. If we
> > > use an uint64_t for an id, there would be plenty room to reserve ids ...
> > >
> > > I'd really prefer if we can avoid using strings and instead using ids.
> >
> > I wish it was that simple and for some names like [anon:.bss] or
> > [anon:dalvik-zygote space] reserving a unique id would work, however
> > some names like [anon:dalvik-/system/framework/boot-core-icu4j.art]
> > are generated dynamically at runtime and include package name.
> > Packages are constantly evolving, new ones are developed, names can
> > change, etc. So assigning a unique id for these names is not really
> > feasible.
>
> I still do not follow. If you need a globaly consistent naming then
> you need clear rules for that, no matter whether that is number or a
> file. How do you handle this with strings currently?

Some names represent standard categories, some are unique. A simple
tool could calculate and report the total for each name, a more
advanced tool might recognize some standard names and process them
differently. From kernel's POV, it's just a name used by the userspace
to categorize anonymous memory areas.

>
> --
> Michal Hocko
> SUSE Labs