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

From: Suren Baghdasaryan <surenb@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>,
	Michal Hocko <mhocko@suse.com>,
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	 Rasmus Villemoes <linux@rasmusvillemoes.dk>,
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	 Tim Murray <timmurray@google.com>
Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting
Date: Wed, 6 Oct 2021 20:01:41 -0700	[thread overview]
Message-ID: <CAJuCfpEZzrN+V2g4+RsRs5v3e60RGvXOCk_X9e3wWkeMBZProg@mail.gmail.com> (raw)
In-Reply-To: <20211006195342.0503b3a3cbcd2c3c3417df46@linux-foundation.org>

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?

>
>
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