On 23.01.24 12:48, Christophe Leroy wrote:
Le 23/01/2024 à 12:38, Ryan Roberts a écrit :
On 23/01/2024 11:31, David Hildenbrand wrote:
If high bits are used for
something else, then we might produce a garbage PTE on overflow, but that
shouldn't really matter I concluded for folio_pte_batch() purposes, we'd not
detect "belongs to this folio batch" either way.
Exactly.
Maybe it's likely cleaner to also have a custom pte_next_pfn() on ppc, I just
hope that we don't lose any other arbitrary PTE bits by doing the pte_pgprot().
I don't see the need for ppc to implement pte_next_pfn().
Agreed.
So likely we should then do on top for powerpc (whitespace damage):
diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index a04ae4449a025..549a440ed7f65 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c
@@ -220,10 +220,7 @@ void set_ptes(struct mm_struct *mm, unsigned long addr,
pte_t *ptep,
break;
ptep++;
addr += PAGE_SIZE;
- /*
- * increment the pfn.
- */
- pte = pfn_pte(pte_pfn(pte) + 1, pte_pgprot((pte)));
+ pte = pte_next_pfn(pte);
}
}
Looks like commit 47b8def9358c ("powerpc/mm: Avoid calling
arch_enter/leave_lazy_mmu() in set_ptes") changed from doing the simple
increment to this more complex approach, but the log doesn't say why.
Right. There was a discussion about it without any conclusion:
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20231024143604.16749-1-aneesh.kumar@xxxxxxxxxxxxx/
As far as understand the simple increment is better on ppc/32 but worse
in ppc/64.
Sounds like we're micro-optimizing for a specific compiler version
output. Hurray.
--
Cheers,
David / dhildenb
