linux-kernel - Re: [Intel-IOMMU 02/10] Library routine for pre-allocat pool handling

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Date:	Sat, 9 Jun 2007 11:47:23 +0200
From:	Andi Kleen <ak@...e.de>
To:	Christoph Lameter <clameter@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Keshavamurthy, Anil S" <anil.s.keshavamurthy@...el.com>,
	linux-kernel@...r.kernel.org, gregkh@...e.de, muli@...ibm.com,
	asit.k.mallick@...el.com, suresh.b.siddha@...el.com,
	arjan@...ux.intel.com, ashok.raj@...el.com, shaohua.li@...el.com,
	davem@...emloft.net
Subject: Re: [Intel-IOMMU 02/10] Library routine for pre-allocat pool handling

> > Now there is a anon dirty limit since a few releases, but I'm not
> > fully convinced it solves the problem completely.
> 
> A gut feeling or is there more?

Lots of other subsystem can allocate a lot of memory
and they usually don't cooperate and have similar dirty limit concepts.
So you could run out of usable memory anyways and then have a similar
issue.

For example a flood of network packets could always steal your
GFP_ATOMIC pools very quickly in the background (gigabit or 10gig 
can transfer a lot of data very quickly) 

Also iirc try_to_free_pages() is not completely fair and might fail
under extreme load for some requesters.

Not requiring memory allocation for any IO would be certainly safer.

Anyways, it's a theoretic question because you can't sleep in 
there anyways unless something drastic changes in the driver interfaces.

-Andi
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