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

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Date:	Mon, 14 Dec 2015 18:11:16 +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 03:51:26PM +0100, Quentin Casasnovas wrote:
...
> 
> Do we want to fold may_expand_anon_vm() into may_expand_vm() (potentially
> passing it the flags/struct file if needed) so there is just one such
> helper function?  Rationale being that it then gets hard to see what
> restricts what, and it's easy to miss one place.

I tried to make the patch small as possible (because otherwise indeed
I would have to pass @vm_file|@...e as additional argument). This won't
be a problem but may_expand_vm is called way more times than
may_expand_anon_vm. That's the only rationale I followed.

> For example, I couldn't find anything preventing a user to
> mmap(MAP_GROWSDOWN) and uses that as a base to get pages that would not be
> accounted for in your patch (making it a poor-man mremap()).

growsup/down stand for stack usage iirc, so it was intentionally
not accounted here.

> 
> 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).
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