linux-kernel - Re: divorce CONFIG_X86_PAE from CONFIG

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Message-ID: <20070612083758.23401.qmail@science.horizon.com>
Date:	12 Jun 2007 04:37:58 -0400
From:	linux@...izon.com
To:	linux-kernel@...r.kernel.org, wli@...omorphy.com
Cc:	linux@...izon.com
Subject: Re: divorce CONFIG_X86_PAE from CONFIG_HIGHMEM64G

Given that incomprehensible help texts are a bit of a pet peeve of mine
(I just last weekend figured out that you don't need to select an I2C
algorithm driver to have working I2c - I had thought it was a "one from
column A, one from column B" thing), let me take a crack...

	PAE doubles the size of each page table entry, increasing
	kernel memory consumption and slowing page table access.
	However, it enables:
	- Addressing more than 4G of physical RAM (CONFIG_HIGHMEM is
	  also required)
	- Marking pages as readable but not executable using the NX
	  (no-execute) bit, which protects applications from stack
	  overflow attacks.
	- Swap files or partitions larger than 64G each.
	  (Only needed with >4G RAM or very heavy tmpfs use.)

	A kernel compiled with this option cannot boot on a processor
	without PAE support.  Enabling this also disables the
	(expert use only) CONFIG_VMSPLIT_[23]G_OPT options.

Does that seem reasonably user-oriented?
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