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

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Message-Id: <20211006195342.0503b3a3cbcd2c3c3417df46@linux-foundation.org>
Date:   Wed, 6 Oct 2021 19:53:42 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     David Hildenbrand <david@...hat.com>,
        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,
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        Axel Rasmussen <axelrasmussen@...gle.com>,
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        Yu Zhao <yuzhao@...gle.com>, Will Deacon <will@...nel.org>,
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        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 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?