Messages in this thread | | | Date | Wed, 9 Aug 2023 13:06:10 +0800 | From | Yan Zhao <> | Subject | Re: [RFC PATCH 3/3] KVM: x86/mmu: skip zap maybe-dma-pinned pages for NUMA migration |
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On Tue, Aug 08, 2023 at 04:56:11PM -0700, Sean Christopherson wrote:
> and then for PG_anon_exclusive > > * ... For now, we only expect it to be > * set on tail pages for PTE-mapped THP. > */ > PG_anon_exclusive = PG_mappedtodisk, >
/* * Depending on the way an anonymous folio can be mapped into a page * table (e.g., single PMD/PUD/CONT of the head page vs. PTE-mapped * THP), PG_anon_exclusive may be set only for the head page or for * tail pages of an anonymous folio. For now, we only expect it to be * set on tail pages for PTE-mapped THP. */ PG_anon_exclusive = PG_mappedtodisk,
Now sure why the comment says PG_anon_exclusive is set only on tail pages for PTE-mapped THP,
what I observed is that only head page of a compound page is set to anon_exclusive.
And the code path is here: __handle_mm_fault |->create_huge_pmd |->do_huge_pmd_anonymous_page //if (vma_is_anonymous(vmf->vma) |->folio = vma_alloc_folio(gfp, HPAGE_PMD_ORDER, vma, haddr, true); |->__do_huge_pmd_anonymous_page(vmf, &folio->page, gfp); |->folio_add_new_anon_rmap |->__page_set_anon_rmap(folio, &folio->page, vma, address, 1); |->SetPageAnonExclusive(page)
And this code path has been present since 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive")
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