diff -urN linux-2.6.10-rc2-mm4/Documentation/kernel-parameters.txt linux-2.6.10-rc2-mm4-mem_hints/Documentation/kernel-parameters.txt
--- linux-2.6.10-rc2-mm4/Documentation/kernel-parameters.txt	2004-12-01 23:50:53.125191440 +0100
+++ linux-2.6.10-rc2-mm4-mem_hints/Documentation/kernel-parameters.txt	2004-12-02 00:14:39.465354776 +0100
@@ -704,6 +704,9 @@
 	mem=nn[KMG]	[KNL,BOOT] Force usage of a specific amount of memory
 			Amount of memory to be used when the kernel is not able
 			to see the whole system memory or for test.
+			[IA-32] Use together with memmap= to avoid physical
+			address space collisions. Without memmap= PCI devices
+			could be placed at addresses belonging to unused RAM.
 
 	mem=nopentium	[BUGS=IA-32] Disable usage of 4MB pages for kernel
 			memory.
diff -urN linux-2.6.10-rc2-mm4/Documentation/memory.txt linux-2.6.10-rc2-mm4-mem_hints/Documentation/memory.txt
--- linux-2.6.10-rc2-mm4/Documentation/memory.txt	2004-10-18 23:55:36.000000000 +0200
+++ linux-2.6.10-rc2-mm4-mem_hints/Documentation/memory.txt	2004-12-02 00:03:01.712429344 +0100
@@ -21,6 +21,8 @@
 All of these problems can be addressed with the "mem=XXXM" boot option
 (where XXX is the size of RAM to use in megabytes).  
 It can also tell Linux to use less memory than is actually installed.
+If you use "mem=" on a machine with PCI, consider using "memmap=" to avoid
+physical address space collisions.
 
 See the documentation of your boot loader (LILO, loadlin, etc.) about
 how to pass options to the kernel.
@@ -44,7 +46,9 @@
 	* Disabling the cache from the BIOS.
 
 	* Try passing the "mem=4M" option to the kernel to limit
-	  Linux to using a very small amount of memory.
+	  Linux to using a very small amount of memory. Use "memmap="-option
+	  together with "mem=" on systems with PCI to avoid physical address
+	  space collisions.
 
 
 Other tricks: