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

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Message-Id: <20070519150934.bdabc9b5.akpm@linux-foundation.org>
Date:	Sat, 19 May 2007 15:09:34 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	William Lee Irwin III <wli@...omorphy.com>
Cc:	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?!

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().

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