Re: [PATCH] 1-2-3 GB

rwhron@earthlink.net
Sat, 12 Jan 2002 16:41:56 -0500


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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