"Aneesh Kumar K.V" [off-list ref] writes:

"Aneesh Kumar K.V" [off-list ref] writes:

quoted

Now that we don't track 4k subpage information we can use 2K PTE
fragments.

Signed-off-by: Aneesh Kumar K.V <redacted>
---
 arch/powerpc/include/asm/book3s/64/hash-64k.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/hash-64k.h b/arch/powerpc/include/asm/book3s/64/hash-64k.h
index 5062c6d423fd..a28dbfe2baed 100644
--- a/arch/powerpc/include/asm/book3s/64/hash-64k.h
+++ b/arch/powerpc/include/asm/book3s/64/hash-64k.h

@@ -39,14 +39,14 @@
  */
 #define PTE_RPN_SHIFT	(30)
 /*
- * we support 8 fragments per PTE page of 64K size.
+ * we support 32 fragments per PTE page of 64K size.
  */
-#define PTE_FRAG_NR	8
+#define PTE_FRAG_NR	32
 /*
  * We use a 2K PTE page fragment and another 4K for storing
  * real_pte_t hash index. Rounding the entire thing to 8K
  */
-#define PTE_FRAG_SIZE_SHIFT  13
+#define PTE_FRAG_SIZE_SHIFT  11
 #define PTE_FRAG_SIZE (1UL << PTE_FRAG_SIZE_SHIFT)

This break THP with 4k hpte support because we need to track 4096
subpage information,  and we have only 2048 bytes after this change.

Another thing I noticed is the impact of not tracking subpage
information. We do see some significant impact as shown by the mmtest
results below. The plan now is to go back to 4K pte framgments but
instead of using 16 bits to track 4k subpage valid bit in pte, we use only 4
bits as the last patch in this series does ("[PATCH V2 10/10]
powerpc/mm: Optmize the hashed subpage iteration"). We will track the
secondary and slot information on the second half. This will result in us using
hidx value 0x0, wrongly. This actually indicate primary hash with slot
number zero. But since we are not going to track individual 4k
subpage information we may using slot 0 wrongly. I checked the existing
code and we should be able to handle that case gracefuly.

I pushed the changes to 

https://github.com/kvaneesh/linux/commits/book3s-pte-format-v2

This needs full round of testing. I only did a sanity test with
4k hash pte config. Will send an updated series once I finish testing.
Meanwhile if you are interested please take a look

-aneesh