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Date: Mon, 30 May 2022 15:56:43 -0400 From: Peter Xu <peterx@...hat.com> To: Mike Kravetz <mike.kravetz@...cle.com> Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, Muchun Song <songmuchun@...edance.com>, Michal Hocko <mhocko@...e.com>, Naoya Horiguchi <naoya.horiguchi@...ux.dev>, James Houghton <jthoughton@...gle.com>, Mina Almasry <almasrymina@...gle.com>, "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>, Anshuman Khandual <anshuman.khandual@....com>, Paul Walmsley <paul.walmsley@...ive.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [RFC PATCH 1/3] hugetlb: skip to end of PT page mapping when pte not present Hi, Mike, On Fri, May 27, 2022 at 03:58:47PM -0700, Mike Kravetz wrote: > +unsigned long hugetlb_mask_last_hp(struct hstate *h) > +{ > + unsigned long hp_size = huge_page_size(h); > + > + if (hp_size == P4D_SIZE) > + return PGDIR_SIZE - P4D_SIZE; > + else if (hp_size == PUD_SIZE) > + return P4D_SIZE - PUD_SIZE; > + else if (hp_size == PMD_SIZE) > + return PUD_SIZE - PMD_SIZE; > + > + return ~(0); > +} How about: unsigned long hugetlb_mask_last_hp(struct hstate *h) { unsigned long hp_size = huge_page_size(h); return hp_size * (PTRS_PER_PTE - 1); } ? This is definitely a good idea, though I'm wondering the possibility to go one step further to make hugetlb pgtable walk just like the normal pages. Say, would it be non-trivial to bring some of huge_pte_offset() into the walker functions, so that we can jump over even larger than PTRS_PER_PTE entries (e.g. when p4d==NULL for 2m huge pages)? It's very possible I overlooked something, though. Thanks, -- Peter Xu
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