linux-kernel - Re: [RFC] A simple way to determine if the kernel needs HIGHMEM64G to be able to use all the installed memory

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Date:	Sat, 7 Mar 2009 22:30:26 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Ozan Çağlayan <ozan@...dus.org.tr>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC] A simple way to determine if the kernel needs HIGHMEM64G
	to be able to use all the installed memory

On Sat, Mar 07, 2009 at 01:04:38PM +0200, Ozan Çağlayan wrote:
> When the installed memory size is >= 4GB, kernel drops some messages like
> 
> Warning only 4GB of memory will be used
> You have to enable HIGHMEM64G.
> 
> I checked that the message comes from arch/x86/init_32.c after checking
> max_pfn.
> 
> I'm quite dumb about the internal structures of the kernel but, wouldn't it
> be possible to create a simple read-only sysfs object like kexec_loaded
> that will contain "1" when the kernel needs HIGHMEM64G to see all of the memory
> and "0" when it doesn't?

Why do you need a file? If kernel says to enable HIGHMEM64G, enable it.

> I think that it would be a nice facility for distribution kernels to detect
> the need for a PAE enabled 32-bit kernel by just reading some /sys/.. entry.
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