linux-kernel - Re: [RFC 1/2] [RFC] mm: Account anon mappings as RLIMIT

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Date:	Mon, 14 Dec 2015 18:43:13 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Quentin Casasnovas <quentin.casasnovas@...cle.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Vegard Nossum <vegard.nossum@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Willy Tarreau <w@....eu>,
	Andy Lutomirski <luto@...capital.net>,
	Kees Cook <keescook@...gle.com>,
	Vladimir Davydov <vdavydov@...tuozzo.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Pavel Emelyanov <xemul@...tuozzo.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC 1/2] [RFC] mm: Account anon mappings as RLIMIT_DATA

On Mon, Dec 14, 2015 at 04:32:34PM +0100, Quentin Casasnovas wrote:
> > 
> > growsup/down stand for stack usage iirc, so it was intentionally
> > not accounted here.
> >
> 
> Right, but in the same vein of Linus saying RLIMIT_DATA is/was useless
> because everyone could use mmap() instead of brk() to get anonymous memory,
> what's the point of restricting "almost-all" anonymous memory if one can
> just use MAP_GROWSDOWN/UP and cause repeated page faults to extend that
> mapping, circumventing your checks?  That makes the new restriction as
> useless as what RLIMIT_DATA used to be, doesn't it?

Not as it were before, but true, using growsdown/up will give a way
to allocate memory not limited byt rlimit-data. (Also I just noted
that I modified mm.h as well, where anon_accountable_mapping
was implemented but forgot to add it into quilt, so this patch
on its own won't compile, don't apply it).

> > > 
> > > I only had a quick look so apologies if this is handled and I missed it :)
> > 
> > thanks for feedback! also take a look on Kostya's patch, I think it's
> > even better approach (and I like it more than mine).
> 
> Ha I'm not subscribed to LKML so I missed those, I suppose you can ignore
> my comments then! :)

https://lkml.org/lkml/2015/12/14/72

Take a look.
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