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Message-ID: <9c465b24-8775-4852-9618-0873cbf2aaf7@redhat.com> Date: Mon, 2 Jun 2025 11:33:07 +0200 From: David Hildenbrand <david@...hat.com> To: Alistair Popple <apopple@...dia.com>, linux-mm@...ck.org Cc: gerald.schaefer@...ux.ibm.com, dan.j.williams@...el.com, jgg@...pe.ca, willy@...radead.org, linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, jhubbard@...dia.com, hch@....de, zhang.lyra@...il.com, debug@...osinc.com, bjorn@...nel.org, balbirs@...dia.com, lorenzo.stoakes@...cle.com, linux-arm-kernel@...ts.infradead.org, loongarch@...ts.linux.dev, linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org, linux-cxl@...r.kernel.org, dri-devel@...ts.freedesktop.org, John@...ves.net Subject: Re: [PATCH 07/12] mm: Remove redundant pXd_devmap calls > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1398,10 +1398,7 @@ static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, > } > > entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); > - if (pfn_t_devmap(pfn)) > - entry = pmd_mkdevmap(entry); > - else > - entry = pmd_mkspecial(entry); > + entry = pmd_mkspecial(entry); > if (write) { I just stumbled over this, and I think there is something off here in the PMD/PUD case. vmf_insert_folio_pmd() does a folio_get() + folio_add_file_rmap_pmd(). But then, we go ahead and turn this into a special mapping by setting it pmd_mkdevmap()/pmd_mkspecial(). Consequently, vm_normal_page_pmd() would ignore them, not following the rules documented for vm_normal_page() and behaving differently than vmf_insert_page_mkwrite()->insert_page(). folio_add_file_rmap_pmd() should never set these things special/devmap in the first place :/ What am I missing? Note that fs/dax.c calls vmf_insert_folio_pmd() for PMDs and vmf_insert_page_mkwrite() for PTEs. Consequently, PTEs will never be marked special (corner case, shared zeropage), but PMDs would always. Hm? -- Cheers, David / dhildenb
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