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Date: Wed, 29 Jun 2022 14:09:35 +0800 From: Muchun Song <songmuchun@...edance.com> To: Mike Kravetz <mike.kravetz@...cle.com> Cc: James Houghton <jthoughton@...gle.com>, Peter Xu <peterx@...hat.com>, David Hildenbrand <david@...hat.com>, David Rientjes <rientjes@...gle.com>, Axel Rasmussen <axelrasmussen@...gle.com>, Mina Almasry <almasrymina@...gle.com>, Jue Wang <juew@...gle.com>, Manish Mishra <manish.mishra@...anix.com>, "Dr . David Alan Gilbert" <dgilbert@...hat.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [RFC PATCH 04/26] hugetlb: make huge_pte_lockptr take an explicit shift argument. On Mon, Jun 27, 2022 at 01:51:53PM -0700, Mike Kravetz wrote: > On 06/24/22 17:36, James Houghton wrote: > > This is needed to handle PTL locking with high-granularity mapping. We > > won't always be using the PMD-level PTL even if we're using the 2M > > hugepage hstate. It's possible that we're dealing with 4K PTEs, in which > > case, we need to lock the PTL for the 4K PTE. > > I'm not really sure why this would be required. > Why not use the PMD level lock for 4K PTEs? Seems that would scale better > with less contention than using the more coarse mm lock. > Your words make me thing of another question unrelated to this patch. We __know__ that arm64 supports continues PTE HugeTLB. huge_pte_lockptr() did not consider this case, in this case, those HugeTLB pages are contended with mm lock. Seems we should optimize this case. Something like: diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 0d790fa3f297..68a1e071bfc0 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -893,7 +893,7 @@ 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) { - if (huge_page_size(h) == PMD_SIZE) + if (huge_page_size(h) <= PMD_SIZE) return pmd_lockptr(mm, (pmd_t *) pte); VM_BUG_ON(huge_page_size(h) == PAGE_SIZE); return &mm->page_table_lock; I did not check if elsewhere needs to be changed as well. Just a primary thought. Thanks. > -- > Mike Kravetz >
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