linux-kernel - Re: [patch 05/11] syslets: core code

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Date:	Wed, 14 Feb 2007 13:09:56 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 05/11] syslets: core code

On Wed, Feb 14, 2007 at 10:46:29AM +0100, Ingo Molnar (mingo@...e.hu) wrote:
> 
> * Evgeniy Polyakov <johnpol@....mipt.ru> wrote:
> 
> > This will end up badly - I used the same approach in the early kevent 
> > days and was proven to have swapable memory for the ring. I think it 
> > would be much better to have userspace allocated ring and use 
> > copy_to_user() there.
> 
> it is a userspace allocated ring - but pinned down by the kernel.

That's a problem - 1000/512 pages per 'usual' thread ends up with the
whole memory locked by malicious/stupid application (at least on Debian
and Mandrake there is no locked memory limit by default). And if such 
a limit exists, this will hurt big-iron applications, which want to used
high-order rings legitimely.

> 	Ingo

-- 
	Evgeniy Polyakov
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