Date: Sat, 12 Jan 2002 16:41:56 -0500
To: Andrea Arcangeli <andrea@suse.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] 1-2-3 GB
Message-ID: <20020112164156.A7069@earthlink.net>
In-Reply-To: <20020112004528.A159@earthlink.net> <20020112125625.E1482@inspiron.school.suse.de>
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In-Reply-To: <20020112125625.E1482@inspiron.school.suse.de>; from andrea@suse.de on Sat, Jan 12, 2002 at 12:56:25PM +0100
From: rwhron@earthlink.net
Sender: linux-kernel-owner@vger.kernel.org

Based on some of the comments in the thread, here
is what I came up with for Configure.help.

Also, in the patch, I had 3GB as the default config
option.  It may be safer to have 1GB as the default
configure option to match the mainline.

--- linux.aa2/Documentation/Configure.help      Fri Jan 11 20:57:58 2002
+++ linux/Documentation/Configure.help  Sat Jan 12 16:29:21 2002
@@ -376,6 +376,59 @@
   Select this if you have a 32-bit processor and more than 4
   gigabytes of physical RAM.

+# Choice: maxvm
+Maximum Virtual Memory
+CONFIG_1GB
+  If you have 4 Gigabytes of physical memory or less, you can change
+  where the where the kernel maps high memory.  If you have less
+  than 1 gigabyte of physical memory, you should disable
+  CONFIG_HIGHMEM4G because you don't need the choices below.
+
+  If you have a large amount of physical memory, all of it may not
+  be "permanently mapped" by the kernel. The physical memory that
+  is not permanently mapped is called "high memory".
+
+  The numbers in the configuration options are not precise because
+  of the kernel's vmalloc() area, and the PCI space on motherboards
+  may vary as well.  Typically there will 128 megabytes less
+  "user memory" mapped than the number in the configuration option.
+  Saying that another way, "high memory" will usually start 128
+  megabytes lower than the configuration option.
+
+  Selecting "05GB" results in a "3.5GB/0.5GB" kernel/user split:
+  3.5 gigabytes are kernel mapped so each process sees a 3.5
+  gigabyte virtual memory space and the remaining part of the 4
+  gigabyte virtual memory space is used by the kernel to permanently
+  map as much physical memory as possible.  On a system with 1 gigabyte
+  of physical memory, you may get 384 megabytes of "user memory" and
+  640 megabytes of "high memory" with this selection.
+
+  Selecting "1GB" results in a "3GB/1GB" kernel/user split:
+  3 gigabytes are mapped so each process sees a 3 gigabyte virtual
+  memory space and the remaining part of the 4 gigabyte virtual memory
+  space is used by the kernel to permanently map as much physical
+  memory as possible.  On a system with 1 gigabyte of memory, you may
+  get 896 MB of "user memory" and 128 megabytes of "high memory"
+
+  Selecting "2GB" results in a "2GB/2GB" kernel/user split:
+  2 gigabytes are mapped so each process sees a 2 gigabyte virtual
+  memory space and the remaining part of the 4 gigabyte virtual memory
+  space is used by the kernel to permanently map as much physical
+  memory as possible.  On a system with 1 to 1.75 gigabytes of
+  physical memory, this option have all make it so no memory is
+  mapped as "high memory".
+
+  Selecting "3GB" results in a "1GB/3GB" kernel/user split:
+  1 gigabyte is mapped so each process sees a 1 gigabyte virtual
+  memory space and the remaining part of the 4 gigabytes of virtual
+  memory space is used by the kernel to permanently map as much
+  physical memory as possible.
+
+  Options "2GB" and "3GB" may expose bugs that were dormant in
+  certain hardware and possibly even the kernel.
+
+  If unsure, say "1GB".
+
 HIGHMEM I/O support
 CONFIG_HIGHIO
   If you want to be able to do I/O to high memory pages, say Y.

-- 
Randy Hron

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