linux-kernel - Re: [rfc] increase struct page size?!

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Message-ID: <4651629B.2050505@aitel.hist.no>
Date:	Mon, 21 May 2007 11:12:59 +0200
From:	Helge Hafting <helge.hafting@...el.hist.no>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	William Lee Irwin III <wli@...omorphy.com>,
	Nick Piggin <npiggin@...e.de>,
	Christoph Lameter <clameter@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-arch@...r.kernel.org
Subject: Re: [rfc] increase struct page size?!

Andrew Morton wrote:
> On Sat, 19 May 2007 11:15:01 -0700 William Lee Irwin III <wli@...omorphy.com> wrote:
>
>   
>> Much the same holds for the atomic_t's; 32 + PAGE_SHIFT is
>> 44 bits or more, about as much as is possible, and one reference per
>> page per page is not even feasible. Full-length atomic_t's are just
>> not necessary.
>>     
>
> You can overflow a page's refcount by mapping it 4G times.  That requires
> 32GB of pagetable memory.  It's quite feasible with remap_file_pages().
>   
But do anybody ever need to do that?
Such an attack is easily thwarted by refusing to map it more
than, say 3G times? 

Helge Hafting
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