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[2003:cb:c738:3100:8133:26cf:7877:94aa]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-436e9e6249csm178599775e9.38.2025.01.14.08.22.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Jan 2025 08:22:17 -0800 (PST) Message-ID: Date: Tue, 14 Jan 2025 17:22:15 +0100 Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 15/26] huge_memory: Add vmf_insert_folio_pud() To: Alistair Popple , akpm@linux-foundation.org, dan.j.williams@intel.com, linux-mm@kvack.org Cc: alison.schofield@intel.com, lina@asahilina.net, zhang.lyra@gmail.com, gerald.schaefer@linux.ibm.com, vishal.l.verma@intel.com, dave.jiang@intel.com, logang@deltatee.com, bhelgaas@google.com, jack@suse.cz, jgg@ziepe.ca, catalin.marinas@arm.com, will@kernel.org, mpe@ellerman.id.au, npiggin@gmail.com, dave.hansen@linux.intel.com, ira.weiny@intel.com, willy@infradead.org, djwong@kernel.org, tytso@mit.edu, linmiaohe@huawei.com, peterx@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, david@fromorbit.com, chenhuacai@kernel.org, kernel@xen0n.name, loongarch@lists.linux.dev References: <60fcfaa3df47885b1df9b064ecb3d4e366fc07e7.1736488799.git-series.apopple@nvidia.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10.01.25 07:00, Alistair Popple wrote: > Currently DAX folio/page reference counts are managed differently to > normal pages. To allow these to be managed the same as normal pages > introduce vmf_insert_folio_pud. This will map the entire PUD-sized folio > and take references as it would for a normally mapped page. > > This is distinct from the current mechanism, vmf_insert_pfn_pud, which > simply inserts a special devmap PUD entry into the page table without > holding a reference to the page for the mapping. > > Signed-off-by: Alistair Popple [...] > +/** > + * vmf_insert_folio_pud - insert a pud size folio mapped by a pud entry > + * @vmf: Structure describing the fault > + * @folio: folio to insert > + * @write: whether it's a write fault > + * > + * Return: vm_fault_t value. > + */ > +vm_fault_t vmf_insert_folio_pud(struct vm_fault *vmf, struct folio *folio, bool write) > +{ > + struct vm_area_struct *vma = vmf->vma; > + unsigned long addr = vmf->address & PUD_MASK; > + pud_t *pud = vmf->pud; > + struct mm_struct *mm = vma->vm_mm; > + spinlock_t *ptl; > + > + if (addr < vma->vm_start || addr >= vma->vm_end) > + return VM_FAULT_SIGBUS; > + > + if (WARN_ON_ONCE(folio_order(folio) != PUD_ORDER)) > + return VM_FAULT_SIGBUS; > + > + ptl = pud_lock(mm, pud); > + if (pud_none(*vmf->pud)) { > + folio_get(folio); > + folio_add_file_rmap_pud(folio, &folio->page, vma); > + add_mm_counter(mm, mm_counter_file(folio), HPAGE_PUD_NR); > + } > + insert_pfn_pud(vma, addr, vmf->pud, pfn_to_pfn_t(folio_pfn(folio)), write); This looks scary at first (inserting something when not taking a reference), but insert_pfn_pud() seems to handle that. A comment here would have been nice. It's weird, though, that if there is already something else, that we only WARN but don't actually return an error. So ... > + spin_unlock(ptl); > + > + return VM_FAULT_NOPAGE; I assume always returning VM_FAULT_NOPAGE, even when something went wrong, is the right thing to do? Apart from that LGTM. -- Cheers, David / dhildenb