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[2003:d8:2f31:700:3851:c66a:b6b9:3490]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568a547d2sm13495403f8f.19.2025.06.17.01.02.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Jun 2025 01:02:46 -0700 (PDT) Message-ID: <044b01ff-2801-4f5b-ac3d-bc9fbd910aa0@redhat.com> Date: Tue, 17 Jun 2025 10:02:44 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/2] mm: Optimize mremap() by PTE batching To: Dev Jain , akpm@linux-foundation.org Cc: Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, jannh@google.com, pfalcato@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, peterx@redhat.com, ryan.roberts@arm.com, mingo@kernel.org, libang.li@antgroup.com, maobibo@loongson.cn, zhengqi.arch@bytedance.com, baohua@kernel.org, anshuman.khandual@arm.com, willy@infradead.org, ioworker0@gmail.com, yang@os.amperecomputing.com, baolin.wang@linux.alibaba.com, ziy@nvidia.com, hughd@google.com References: <20250610035043.75448-1-dev.jain@arm.com> <20250610035043.75448-3-dev.jain@arm.com> <43d9cb6e-1b8f-47b9-8c19-58fc7c74a71e@redhat.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: 8bit >> -               pte = get_and_clear_full_ptes(mm, old_addr, old_ptep, >> nr_ptes, 0); >> -               pte = move_pte(pte, old_addr, new_addr); >> -               pte = move_soft_dirty_pte(pte); >> - >> -               if (need_clear_uffd_wp && pte_marker_uffd_wp(pte)) >> -                       pte_clear(mm, new_addr, new_ptep); >> -               else { >> -                       if (need_clear_uffd_wp) { >> -                               if (pte_present(pte)) >> -                                       pte = pte_clear_uffd_wp(pte); >> -                               else if (is_swap_pte(pte)) >> + >> +                       pte = get_and_clear_full_ptes(mm, old_addr, >> old_ptep, >> +                                                     nr_ptes, 0); >> +                       /* >> +                        * Moving present PTEs requires special care >> on some >> +                        * archs. >> +                        */ >> +                       pte = move_pte(pte, old_addr, new_addr); >> +                       /* make userspace aware that this pte moved. */ >> +                       pte = pte_mksoft_dirty(pte); >> +                       if (need_clear_uffd_wp) >> +                               pte = pte_clear_uffd_wp(pte); >> +                       set_ptes(mm, new_addr, new_ptep, pte, nr_ptes); >> +               } else if (need_clear_uffd_wp && >> pte_marker_uffd_wp(pte)) { >> +                       pte_clear(mm, old_addr, old_ptep); >> +               } else { >> +                       pte_clear(mm, old_addr, old_ptep); > > Should pte_clear be included here? It is currently being done only for > the case > > need_clear_uffd_wp && pte_marker_uffd_wp(). We always cleared the old pte (using get_and_clear_*, which is not required if we already know that it is !present). The case you mean was what I describe here: >> >> >> >> Note that I don't know why we had the existing >> >> -               if (need_clear_uffd_wp && pte_marker_uffd_wp(pte)) >> -                       pte_clear(mm, new_addr, new_ptep); >> >> >> I thought we would always expect that the destination pte is already >> pte_none() ? So clearing the destination PTE can be dropped if we didn't move in the first place. -- Cheers, David / dhildenb