Re: [RFC PATCH v4 14/16] powerpc/64s: Use contiguous PMD/PUD instead of HUGEPD
From: Oscar Salvador <hidden>
Date: 2024-05-29 09:23:22
Also in:
linuxppc-dev, lkml
On Mon, May 27, 2024 at 03:30:12PM +0200, Christophe Leroy wrote:
On book3s/64, the only user of hugepd is hash in 4k mode. All other setups (hash-64, radix-4, radix-64) use leaf PMD/PUD. Rework hash-4k to use contiguous PMD and PUD instead. In that setup there are only two huge page sizes: 16M and 16G. 16M sits at PMD level and 16G at PUD level.
On 4k mode, PMD_SIZE is 2MB and PUD_SIZE is 256MB, right?
+static inline unsigned long hash__pte_update(struct mm_struct *mm,
+ unsigned long addr,
+ pte_t *ptep, unsigned long clr,
+ unsigned long set,
+ int huge)
+{
+ unsigned long old;
+
+ old = hash__pte_update_one(ptep, clr, set);
+
+ if (IS_ENABLED(CONFIG_PPC_4K_PAGES) && huge) {
+ unsigned int psize = get_slice_psize(mm, addr);
+ int nb, i;
+
+ if (psize == MMU_PAGE_16M)
+ nb = SZ_16M / PMD_SIZE;
+ else if (psize == MMU_PAGE_16G)
+ nb = SZ_16G / PUD_SIZE;
+ else
+ nb = 1;On 4K, hugepages are either 16M or 16G. How can we end up in a situation whwere the is pte is huge, but is is neither MMU_PAGE_16G nor MMU_PAGE_16M?
quoted hunk ↗ jump to hunk
diff --git a/arch/powerpc/mm/book3s64/hugetlbpage.c b/arch/powerpc/mm/book3s64/hugetlbpage.c index 5a2e512e96db..83c3361b358b 100644 --- a/arch/powerpc/mm/book3s64/hugetlbpage.c +++ b/arch/powerpc/mm/book3s64/hugetlbpage.c@@ -53,6 +53,16 @@ int __hash_page_huge(unsigned long ea, unsigned long access, unsigned long vsid, /* If PTE permissions don't match, take page fault */ if (unlikely(!check_pte_access(access, old_pte))) return 1; + /* + * If hash-4k, hugepages use seeral contiguous PxD entries
'several'
+ * so bail out and let mm make the page young or dirty
+ */
+ if (IS_ENABLED(CONFIG_PPC_4K_PAGES)) {
+ if (!(old_pte & _PAGE_ACCESSED))
+ return 1;
+ if ((access & _PAGE_WRITE) && !(old_pte & _PAGE_DIRTY))
+ return 1;I have 0 clue about this code. What would happen if we do not bail out? -- Oscar Salvador SUSE Labs