On Fri, 12 Dec 2008 01:22:32 +0300
Yuri Tikhonov [off-list ref] wrote:

quoted

so how about avoiding the nasty ifdefs and doing

 I'm OK with the approach below, but, leading resulting to the same, 
this involves some overhead to the code where there was no this 
overhead before this patch: e.g. your implementation is finally boils 
down to ~5 times more processor instructions than there were before,
plus operations with stack for the 'm' variable.

 On the other hand, my approach with nasty (I agree) ifdefs doesn't 
lead to overheads to the code which does not need this: i.e. the most 
common situation of small PAGE_SIZEs. Big PAGE_SIZE is the exception, 
so I believe that the more common cases should not suffer because of 
this.

yes, but...

quoted

--- a/kernel/fork.c~fork_init-fix-division-by-zero
+++ a/kernel/fork.c

@@ -69,6 +69,7 @@
 #include <asm/mmu_context.h>
 #include <asm/cacheflush.h>
 #include <asm/tlbflush.h>
+#include <asm/div64.h>
 
 /*
  * Protected counters by write_lock_irq(&tasklist_lock)

@@ -185,10 +186,15 @@ void __init fork_init(unsigned long memp

This is __init code and it gets thrown away after bootup.