[PATCH] ppc: Add support for bigger page sizes than 4KB on PPC44x

[Yuri Tikhonov]

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.
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