linux-kernel - Re: controlling mmap()'d vs read/write() pages

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Date:	Fri, 23 Mar 2007 16:57:40 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Dave Hansen <hansendc@...ibm.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, containers@...ts.osdl.org,
	linux-kernel@...r.kernel.org, menage@...gle.com,
	Andrew Morton <akpm@...ux-foundation.org>, xemul@...ru
Subject: Re: controlling mmap()'d vs read/write() pages

Eric W. Biederman wrote:
> Dave Hansen <hansendc@...ibm.com> writes:
> 
> 
>>So, I think we have a difference of opinion.  I think it's _all_ about
>>memory pressure, and you think it is _not_ about accounting for memory
>>pressure. :)  Perhaps we mean different things, but we appear to
>>disagree greatly on the surface.
> 
> 
> I think it is about preventing a badly behaved container from having a
> significant effect on the rest of the system, and in particular other
> containers on the system.

That's Dave's point, I believe. Limiting mapped memory may be
mostly OK for well behaved applications, but it doesn't do anything
to stop bad ones from effectively DoSing the system or ruining any
guarantees you might proclaim (not that hard guarantees are always
possible without using virtualisation anyway).

This is why I'm surprised at efforts that go to such great lengths
to get accounting "just right" (but only for mmaped memory). You
may as well not even bother, IMO.

Give me an RSS limit big enough to run a couple of system calls and
a loop...

-- 
SUSE Labs, Novell Inc.
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