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

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Date:   Thu, 7 Oct 2021 09:27:39 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Suren Baghdasaryan <surenb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Michal Hocko <mhocko@...e.com>, John Hubbard <jhubbard@...dia.com>,
        Pavel Machek <pavel@....cz>, 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 <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, Rasmus Villemoes <linux@...musvillemoes.dk>,
        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 07.10.21 05:01, Suren Baghdasaryan wrote:
> On Wed, Oct 6, 2021 at 7:53 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>>
>> On Wed, 6 Oct 2021 19:46:57 -0700 Suren Baghdasaryan <surenb@...gle.com> wrote:
>>
>>>>>>> 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.
>>>>>>
>>>>>> Valuable information
>>>>>
>>>>> Yeah, I should have described it clearer the first time around.
>>>>
>>>> If it gets this fancy then the 80 char limit is likely to become a
>>>> significant limitation and the choice should be explained & justified.
>>>>
>>>> Why not 97?  1034?  Why not just strndup_user() and be done with it?
>>>
>>> The original patch from 8 years ago used 256 as the limit but Rasmus
>>> argued that the string content should be human-readable, so 80 chars
>>> seems to be a reasonable limit (see:
>>> https://lore.kernel.org/all/d8619a98-2380-ca96-001e-60fe9c6204a6@rasmusvillemoes.dk),
>>> which makes sense to me. We should be able to handle the 80 char limit
>>> by trimming it before calling prctl().
>>
>> What's the downside to making it unlimited?
> 
> If we ignore the human-readability argument, I guess the possibility
> of abuse and increased memory consumption? I'm guessing parsing such a
> string is also easier if there is a known limit?

64k * 80 bytes already makes me nervous enough :)


-- 
Thanks,

David / dhildenb