Re: 2G memory split

From: Ingo Molnar <mingo@elte.hu>
To: Jens Axboe <axboe@suse.de>
Cc: Byron Stanoszek <gandalf@winds.org>,
	linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>,
	Linus Torvalds <torvalds@osdl.org>
Subject: Re: 2G memory split
Date: Tue, 10 Jan 2006 15:44:12 +0100	[thread overview]
Message-ID: <20060110144412.GA9295@elte.hu> (raw)
In-Reply-To: <20060110143931.GM3389@suse.de>

* Jens Axboe <axboe@suse.de> wrote:

> +	  Select the wanted split between kernel and user memory.
> +
> +	  If the address range available to the kernel is less than the
> +	  physical memory installed, the remaining memory will be available
> +	  as "high memory". Accessing high memory is a little more costly
> +	  than low memory, as it needs to be mapped into the kernel first.

make it _ALOT_ more clear that mere mortals should not touch this 
option! Also, you do not mention the userspace-VM fragmentation issues.  
Plus, if a user uses a 2G/2G split with more than 2G of RAM, the kernel 
should print a warning that it's running with a non-default split. Do 
the same if the user uses a non-default split with less than 960MB of 
RAM.

> +
> +	  Note that selecting anything but the default 3G/1G split will make
> +	  your kernel incompatible with binary only modules.

it's not 'will' but 'may', and even then, tons of .config things can 
break bin-only modules, so just skip this paragraph.

looks good to me otherwise, with the text fixes it's:

Acked-by: Ingo Molnar <mingo@elte.hu>

	Ingo