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Message-ID: <6841026c50e57_249110022@dwillia2-xfh.jf.intel.com.notmuch> Date: Wed, 4 Jun 2025 19:35:24 -0700 From: Dan Williams <dan.j.williams@...el.com> To: Alistair Popple <apopple@...dia.com>, <linux-mm@...ck.org> CC: Alistair Popple <apopple@...dia.com>, <gerald.schaefer@...ux.ibm.com>, <dan.j.williams@...el.com>, <jgg@...pe.ca>, <willy@...radead.org>, <david@...hat.com>, <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 Alistair Popple wrote: > DAX was the only thing that created pmd_devmap and pud_devmap entries > however it no longer does as DAX pages are now refcounted normally and > pXd_trans_huge() returns true for those. Therefore checking both pXd_devmap > and pXd_trans_huge() is redundant and the former can be removed without > changing behaviour as it will always be false. > > Signed-off-by: Alistair Popple <apopple@...dia.com> [..] > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 8d9d706..31b4110 100644 > --- 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) { > entry = pmd_mkyoung(pmd_mkdirty(entry)); > entry = maybe_pmd_mkwrite(entry, vma); > @@ -1535,10 +1530,7 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr, > } > > entry = pud_mkhuge(pfn_t_pud(pfn, prot)); > - if (pfn_t_devmap(pfn)) > - entry = pud_mkdevmap(entry); > - else > - entry = pud_mkspecial(entry); > + entry = pud_mkspecial(entry); Wait, why are my gup tests passing? If all dax pages are special, then vm_normal_page() should never find them and gup should fail. ...oh, but vm_normal_page_p[mu]d() is not used in the gup path, and 'special' is not set in the pte path. Yuck, that feels subtle. I think for any p[mu]d where p[mu]d_page() is ok to use should never set 'special', right?
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