On Wed, May 29, 2024 at 10:14:15AM +0000, Christophe Leroy wrote:

Le 29/05/2024 à 12:09, Oscar Salvador a écrit :

quoted

On Wed, May 29, 2024 at 09:49:48AM +0000, Christophe Leroy wrote:

quoted

Doesn't really matter if it's PUD or PMD at this point. On a 32 bits
kernel it will be all PMD while on a 64 bits kernel it is both PMD and PUD.

At the time being (as implemented with hugepd), Linux support 4M, 16M,
64M, 256M and 1G (Shifts 22, 24, 26, 28, 30)

The hardware supports the following page sizes, and encodes them on 4
bits allthough it is not directly a shift. Maybe it would be better to
use that encoding after all:

I think so.

quoted

0001 4 Kbytes (Shift 12)
0010 16 Kbytes (Shift 14)
0011 64 Kbytes (Shift 16)
0100 256 Kbytes (Shift 18)
0101 1 Mbyte (Shift 20)
0110 4 Mbytes (Shift 22)
0111 16 Mbytes (Shift 24)
1000 64 Mbytes (Shift 26)
1001 256 Mbytes (Shift 28)
1010 1 Gbyte (e500v2 only) (Shift 30)
1011 4 Gbytes (e500v2 only) (Shift 32)

You say hugehages start at 2MB (shift 21), but you say that the smallest hugepage
Linux support is 4MB (shift 22).?

No I say PMD_SIZE is 2MB on e500 with 64 bits PTE and at the time being 
Linux powerpc implementation for e500 supports sizes 4M, 16M, 64M, 256M 
and 1G.

Got it. I got confused.


-- 
Oscar Salvador
SUSE Labs