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

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Message-ID: <6b15c682-72eb-724d-bc43-36ae6b79b91a@redhat.com>
Date:   Wed, 6 Oct 2021 11:27:45 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>, John Hubbard <jhubbard@...dia.com>
Cc:     Suren Baghdasaryan <surenb@...gle.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>,
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        vincenzo.frascino@....com,
        Chinwen Chang (張錦文) 
        <chinwen.chang@...iatek.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 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.

-- 
Thanks,

David / dhildenb