linux-kernel - [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, 07 Mar 2009 13:04:38 +0200
From:	Ozan Çağlayan <ozan@...dus.org.tr>
To:	linux-kernel@...r.kernel.org
Subject: [RFC] A simple way to determine if the kernel needs HIGHMEM64G to
 be able to use all the installed memory

Hi,

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?

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.

Thanks,

-- 

Ozan Çağlayan
<ozan_at_pardus.org.tr>
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