Re: [PATCH 1/4] hugetlb: skip to end of PT page mapping when pte not present
From: Peter Xu <peterx@redhat.com>
Date: 2022-06-17 14:15:45
Also in:
linux-arm-kernel, linux-mips, linux-mm, linux-s390, linux-sh, lkml, sparclinux
Hi, Mike, On Thu, Jun 16, 2022 at 02:05:15PM -0700, Mike Kravetz wrote:
quoted hunk ↗ jump to hunk
@@ -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?
+ 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? Thanks, -- Peter Xu