linux-kernel - Re: [PATCH 1/2] rcfs core patch

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Date:	Fri, 9 Mar 2007 14:29:22 +0100
From:	Herbert Poetzl <herbert@...hfloor.at>
To:	Kirill Korotaev <dev@...ru>
Cc:	Paul Menage <menage@...gle.com>, pj@....com,
	"Eric W. Biederman" <ebiederm@...ssion.com>, winget@...gle.com,
	containers@...ts.osdl.org, akpm@...ux-foundation.org,
	ckrm-tech@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	xemul@...ru
Subject: Re: [PATCH 1/2] rcfs core patch

On Fri, Mar 09, 2007 at 12:07:27PM +0300, Kirill Korotaev wrote:
>>  nobody actually cares about a precise accounting and
>>  calculating shares or partitions of whatever resource,
>>  all that matters is that you have a way to prevent a
>>  potential hostile environment from sucking up all your
>>  resources (or even a single one) resulting in a DoS

> This is not true. People care. Reasons:
>   - resource planning
>   - fairness
>   - guarantees

let me make that a little more clear ...

_nobody_ cares wether a shared memory page is
accounted as full page or as fraction of a page
(depending on the number of guests sharing it)
as long as the accounted amount is substracted
correctly when the page is disposed 

so there _is_ a difference between _false_
accounting (which seems what you are referring
to in the next paragraph) and imprecise, but
consistant accounting (which is what I was 
talking about)

best,
Herbert

>   What you talk is about security only. Not the above issues.
>   So good precision is required. If there is no precision at all,
>   security sucks as well and can be exploited, e.g. for CPU
>   schedulers doing an accounting based on jiffies accounting in
>   scheduler_tick() it is easy to build an application consuming
>   90% of CPU, but ~0% from scheduler POV.

> Kirill
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