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

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Message-ID: <b606021e-0afa-a509-84c4-2988d77f68bc@rasmusvillemoes.dk>
Date:   Fri, 8 Oct 2021 09:25:10 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     John Hubbard <jhubbard@...dia.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Kees Cook <keescook@...omium.org>
Cc:     Michal Hocko <mhocko@...e.com>, Pavel Machek <pavel@....cz>,
        David Hildenbrand <david@...hat.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>,
        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,
        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>
Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting

On 07/10/2021 21.02, John Hubbard wrote:
> On 10/7/21 11:50, Suren Baghdasaryan wrote:
> ...

>>>> The desire is for one of these two parties to be a human who can get
>>>> the data and use it as is without additional conversions.
>>>> /proc/$pid/maps could report FD numbers instead of pathnames, which
>>>> could be converted to pathnames in userspace. However we do not do
>>>> that because pathnames are more convenient for humans to identify a
>>>> specific resource. Same logic applies here IMHO.
>>>
>>> Yes, please. It really seems like the folks that are interested in this
>>> feature want strings. (I certainly do.) For those not interested in the
>>> feature, it sounds like a CONFIG to keep it away would be sufficient.
>>> Can we just move forward with that?
>>
>> Would love to if others are ok with this.
>>
> 
> If this doesn't get accepted, then another way forward would to continue
> the ideas above to their logical conclusion, and create a new file system:
> vma-fs. 

Or: Why can't the library/application that wants a VMA backed by memory
to have some associated name not just

  fd = open("/run/named-vmas/foobar#24", O_CLOEXEC|O_RDWR|O_EXCL|O_CREAT);
  unlink("/run/named-vmas/foobar#24");
  ftruncate(fd, ...);
  mmap(fd);

where /run/named-vmas is a tmpfs (probably with some per-user/per-app
subdirs). That requires no changes in the kernel at all. Yes, it lacks
the automatic cleanup of using real anon mmap in case there's a crash
between open and unlink, but in an environment like Android that should
be solvable.

Rasmus