On 6/18/2022 1:17 AM, Mike Kravetz wrote:
On 06/17/22 10:15, Peter Xu wrote:
Hi, Mike,
On Thu, Jun 16, 2022 at 02:05:15PM -0700, Mike Kravetz wrote:
@@ -6877,6 +6896,39 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
return (pte_t *)pmd;
}
+/*
+ * Return a mask that can be used to update an address to the last huge
+ * page in a page table page mapping size. Used to skip non-present
+ * page table entries when linearly scanning address ranges. Architectures
+ * with unique huge page to page table relationships can define their own
+ * version of this routine.
+ */
+unsigned long hugetlb_mask_last_page(struct hstate *h)
+{
+ unsigned long hp_size = huge_page_size(h);
+
+ switch (hp_size) {
+ case P4D_SIZE:
+ return PGDIR_SIZE - P4D_SIZE;
+ case PUD_SIZE:
+ return P4D_SIZE - PUD_SIZE;
+ case PMD_SIZE:
+ return PUD_SIZE - PMD_SIZE;
+ default:
Should we add a WARN_ON_ONCE() if it should never trigger?
Sure. I will add this.
+ break; /* Should never happen */
+ }
+
+ return ~(0UL);
+}
+
+#else
+
+/* See description above. Architectures can provide their own version. */
+__weak unsigned long hugetlb_mask_last_page(struct hstate *h)
+{
+ return ~(0UL);
I'm wondering whether it's better to return 0 rather than ~0 by default.
Could an arch with !CONFIG_ARCH_WANT_GENERAL_HUGETLB wrongly skip some
valid address ranges with ~0, or perhaps I misread?
Thank you, thank you, thank you Peter!
Yes, the 'default' return for hugetlb_mask_last_page() should be 0. If
there is no 'optimization', we do not want to modify the address so we
want to OR with 0 not ~0. My bad, I must have been thinking AND instead
of OR.
I will change here as well as in Baolin's patch.
Ah, I also overlooked this. Thanks Peter, and thanks Mike for updating.
