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

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Message-ID: <YV6o3Bsb4f87FaAy@dhcp22.suse.cz>
Date:   Thu, 7 Oct 2021 09:59:24 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Suren Baghdasaryan <surenb@...gle.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>,
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        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 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?

-- 
Michal Hocko
SUSE Labs