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Date:   Thu, 7 Oct 2021 12:15:27 +0200
From:   Pavel Machek <pavel@ucw.cz>
To:     Rasmus Villemoes <linux@rasmusvillemoes.dk>
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Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting
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Hi!

> >> Hmm, so the suggestion is to have some directory which contains files
> >> representing IDs, each containing the string name of the associated
> >> vma? Then let's say we are creating a new VMA and want to name it. We
> >> would have to scan that directory, check all files and see if any of
> >> them contain the name we want to reuse the same ID.
> >=20
> > I believe Pavel meant something as simple as
> > $ YOUR_FILE=3D$YOUR_IDS_DIR/my_string_name
> > $ touch $YOUR_FILE
> > $ stat -c %i $YOUR_FILE
>=20
> So in terms of syscall overhead, that would be open(..., O_CREAT |
> O_CLOEXEC), fstat(), close() - or one could optimistically start by

You could get to two if you used mkdir instead of open.

> > YOUR_IDS_DIR can live on a tmpfs and you can even implement a policy on
> > top of that (who can generate new ids, gurantee uniqness etc...).
> >=20
> > The above is certainly not for free of course but if you really need a
> > system wide consistency when using names then you need some sort of
> > central authority. How you implement that is not all that important
> > but I do not think we want to handle that in the kernel.
>=20
> IDK. If the whole thing could be put behind a CONFIG_ knob, with _zero_
> overhead when not enabled (and I'm a bit worried about all the functions
> that grow an extra argument that gets passed around), I don't mind the
> string interface. But I don't really have a say either way.

If this is ever useful outside of Android, eventually distros will
have it enabled.

Best regards,
								Pavel
--=20
http://www.livejournal.com/~pavelmachek

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