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[2003:d8:2f34:a300:1c2c:f35e:e8e5:488e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-450d7f8edf9sm120150665e9.3.2025.06.02.05.20.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Jun 2025 05:20:54 -0700 (PDT) Message-ID: <799691d6-d9dd-43fd-805e-7dce6efff3e6@redhat.com> Date: Mon, 2 Jun 2025 14:20:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 07/12] mm: Remove redundant pXd_devmap calls From: David Hildenbrand To: Alistair Popple , linux-mm@kvack.org Cc: 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 References: <2ee5a64581d2c78445e5c4180d7eceed085825ca.1748500293.git-series.apopple@nvidia.com> <9c465b24-8775-4852-9618-0873cbf2aaf7@redhat.com> Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 0A7FA120003 X-Rspamd-Server: rspam09 X-Stat-Signature: hgkpop5tp9wwpfi56zg4cp9y1go5wson X-HE-Tag: 1748866859-537341 X-HE-Meta: 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 ZLqKo173 p2QKA9sOSq/GysZ4aZFghZ+nOXOqI0gh4pdfv1JZxd4iJWFwA+WQfDE16CDSVtigc+9d888b1iXQxloBV+ktp16LgkNnSrT7RXvbT2qT8w2M3Bz2qyN2AjcsSZr3oBF0YoFm+H9EnmxmcnA2fwd2U9F7gjxLomWz6FxxzWeXkB5ErRTL/t1rKg+bG+JGFwWTxXm/6PsVoMF3wRIXiaZnfCkywXF2sYGkVXenGpGJBVLT9vcNQY3Okytn4ouytFON8ZLGoFecCYpb2mS9QISGs+fBzBj3zuawkp0AFSGeGuviJDuPR0JiLJf/XBq7MJJi83prg5QlVYNPGgCyqskeFsj4khj5cB3/TMmxtt5MHpmLBI+/eyQsVYxjETIr8q0CXpzWjBG6z4v7vosG43JziHGMJDqP8r1e23kl2MyQ/zzkaLLmlemHVGYJjacg0ilvyeiryGZtj3FrnXRwxcSOkaIBZF1yAuMUwmCshEikYqIBt2y5xngo+nCOWz55TjkBl9bG9GGUnABiVh4Q= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 02.06.25 11:33, David Hildenbrand wrote: >> --- 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? What an ugly piece of crap this pmd handling code is. Just noting because I stumbled over that myself: pmd_mkdevmap() does *not* imply pmd_special(). ... in contrast to pte_mkdevmap(), which will imply pte_special(). -- Cheers, David / dhildenb