linux-kernel - Re: why choose 896MB to the start point of ZONE

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Message-ID: <4BBB8F07.60401@zytor.com>
Date:	Tue, 06 Apr 2010 12:44:07 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Frank Hu <frank.hu.2001@...il.com>
CC:	Joel Fernandes <agnel.joel@...il.com>,
	hayfeng Lee <teklife.kernel@...il.com>,
	linux-kernel@...r.kernel.org, linux-kernel@...kernel.org,
	kernelnewbies@...linux.org
Subject: Re: why choose 896MB to the start point of ZONE_HIGHMEM

On 04/06/2010 12:20 PM, Frank Hu wrote:
>>
>> The ELF ABI specifies that user space has 3 GB available to it.  That
>> leaves 1 GB for the kernel.  The kernel, by default, uses 128 MB for I/O
>> mapping, vmalloc, and kmap support, which leaves 896 MB for LOWMEM.
>>
>> All of these boundaries are configurable; with PAE enabled the user
>> space boundary has to be on a 1 GB boundary.
>>
> 
> the VM split is also configurable when building the kernel (for 32-bit
> processors).

I did say "all these boundaries are configurable".  Rather explicitly.

	-hpa
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