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[2003:d8:2f31:700:3851:c66a:b6b9:3490]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a578510edcsm9430995f8f.8.2025.06.17.02.49.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Jun 2025 02:49:22 -0700 (PDT) Message-ID: <6bb233ef-5e56-4546-b571-6a5f052d8b45@redhat.com> Date: Tue, 17 Jun 2025 11:49:20 +0200 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 06/14] mm/huge_memory: Remove pXd_devmap usage from insert_pXd_pfn() To: Alistair Popple , akpm@linux-foundation.org Cc: linux-mm@kvack.org, gerald.schaefer@linux.ibm.com, dan.j.williams@intel.com, jgg@ziepe.ca, willy@infradead.org, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, zhang.lyra@gmail.com, debug@rivosinc.com, bjorn@kernel.org, balbirs@nvidia.com, lorenzo.stoakes@oracle.com, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-cxl@vger.kernel.org, dri-devel@lists.freedesktop.org, John@Groves.net, m.szyprowski@samsung.com References: <67bc382c49ed8b165cfbd927886372272c35f508.1750075065.git-series.apopple@nvidia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 16.06.25 13:58, Alistair Popple wrote: > Nothing uses PFN_DEV anymore so no need to create devmap pXd's when > mapping a PFN. Instead special mappings will be created which ensures > vm_normal_page_pXd() will not return pages which don't have an > associated page. This could change behaviour slightly on architectures > where pXd_devmap() does not imply pXd_special() as the normal page > checks would have fallen through to checking VM_PFNMAP/MIXEDMAP instead, > which in theory at least could have returned a page. > > However vm_normal_page_pXd() should never have been returning pages for > pXd_devmap() entries anyway, so anything relying on that would have been > a bug. > > Signed-off-by: Alistair Popple > > --- > > Changes since v1: > > - New for v2 > --- > mm/huge_memory.c | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index b096240..6514e25 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1415,11 +1415,7 @@ static int insert_pmd(struct vm_area_struct *vma, unsigned long addr, > add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR); > } else { > entry = pmd_mkhuge(pfn_t_pmd(fop.pfn, prot)); > - > - if (pfn_t_devmap(fop.pfn)) > - entry = pmd_mkdevmap(entry); > - else > - entry = pmd_mkspecial(entry); > + entry = pmd_mkspecial(entry); > } > if (write) { > entry = pmd_mkyoung(pmd_mkdirty(entry)); > @@ -1565,11 +1561,7 @@ static void insert_pud(struct vm_area_struct *vma, unsigned long addr, > add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PUD_NR); > } else { > entry = pud_mkhuge(pfn_t_pud(fop.pfn, prot)); > - > - if (pfn_t_devmap(fop.pfn)) > - entry = pud_mkdevmap(entry); > - else > - entry = pud_mkspecial(entry); > + entry = pud_mkspecial(entry); > } > if (write) { > entry = pud_mkyoung(pud_mkdirty(entry)); Why not squash this patch into #3, and remove the pmd_special() check from vm_normal_page_pmd() in the same go? Seems wrong to handle the PMD/PUD case separately. But now I am confused why some pte_devmap() checks are removed in patch #3, while others are removed in #7. Why not split it up into (a) stop setting p*_devmap() and (b) remove p*_devmap(). Logically makes more sense to me ... :) -- Cheers, David / dhildenb