Messages in this thread | | | Date | Tue, 23 Aug 2022 18:12:30 +0800 | Subject | Re: [PATCH v2 4/5] mm/hugetlb: use PMD page lock to protect CONT-PTE entries | From | Baolin Wang <> |
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On 8/23/2022 4:14 PM, David Hildenbrand wrote: > On 23.08.22 09:50, Baolin Wang wrote: >> Considering the pmd entries of a CONT-PMD hugetlb can not span on >> multiple PMDs, we can change to use the PMD page lock, which can >> be much finer grain that lock in the mm. >> >> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> >> --- >> include/linux/hugetlb.h | 12 ++++++++++-- >> 1 file changed, 10 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h >> index 3a96f67..d4803a89 100644 >> --- a/include/linux/hugetlb.h >> +++ b/include/linux/hugetlb.h >> @@ -892,9 +892,17 @@ static inline gfp_t htlb_modify_alloc_mask(struct hstate *h, gfp_t gfp_mask) >> static inline spinlock_t *huge_pte_lockptr(struct hstate *h, >> struct mm_struct *mm, pte_t *pte) >> { >> - VM_BUG_ON(huge_page_size(h) == PAGE_SIZE); >> + unsigned long hp_size = huge_page_size(h); >> >> - if (huge_page_size(h) == PMD_SIZE) { >> + VM_BUG_ON(hp_size == PAGE_SIZE); >> + >> + /* >> + * Considering CONT-PMD size hugetlb, since the CONT-PMD entry >> + * can not span multiple PMDs, then we can use the fine grained >> + * PMD page lock. >> + */ >> + if (hp_size == PMD_SIZE || >> + (hp_size > PMD_SIZE && hp_size < PUD_SIZE)) { >> return pmd_lockptr(mm, (pmd_t *) pte); >> } else if (huge_page_size(h) < PMD_SIZE) { >> unsigned long mask = ~(PTRS_PER_PTE * sizeof(pte_t) - 1); > > Is there a measurable performance gain? IOW, do we really care?
IMO, It's just a theoretical analysis now:) Let me think about how to measure the performance gain.
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