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Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting
To:     Suren Baghdasaryan <surenb@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
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From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <3645f74d-54b4-9223-1d53-75cade471fad@redhat.com>
Date:   Thu, 7 Oct 2021 09:27:39 +0200
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On 07.10.21 05:01, Suren Baghdasaryan wrote:
> On Wed, Oct 6, 2021 at 7:53 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>>
>> On Wed, 6 Oct 2021 19:46:57 -0700 Suren Baghdasaryan <surenb@google.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