On Tue Mar 13 18:12:14 EST 2007, Benjamin Herrenschmidt wrote:

- You only adapted head_4xx.S but the config option is global to all of
arch/ppc, thus changing it will probably break everything else. Make
sure the option is done in such a way that it can't be changed or the
kernel doesn't build if changed for a processor family where you haven't
implemented the support

 The configuration option we had introduced changes the global PPC PAGE_SIZE 
definition indeed. To let changing the PAGE_SIZE from the configuration menu 
for the 44x processors only the following modification of the 
arch/ppc/Kconfig file might make sense:

 - int "Page size (12=>4KB; 16=>64KB)"
+ int "Page size (12=>4KB; 16=>64KB)" if 44x

 For other than 44x processors the PPC_PAGE_SHIFT value will be unchangeable 
from the configuration menu and set to default  value 12 ( PAGE_SIZE = 4 KB).

- Have you tried other page sizes ? How hard would it be to support 16K
and what kind of performance numbers do you get with 16K ? It's a better
compromise for some applications as 64K causes significant bloat of the
page cache (among other things).

 To support 16K, one more bunch of definitions should be calculated and added 
to the include/asm/ppc_page_asm.h file (for PAGE_SHIFT = 14). Attached is the 
patch that adds 16KB PAGE_SIZE capability for the ppc44x processors.

 Regards, Yuri.