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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 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 Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 456F940008 X-Stat-Signature: 39g1y1qq4uytsqpj3zo11m6a5yzmifew X-Rspam-User: X-HE-Tag: 1750147373-642050 X-HE-Meta: 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 ku9IBiNT 2wNiCmVqD4NFjtJqi/WQLiRw3oMKZ+vZ/ydtQfOm2zeLb+tkoBN1st3NfH5B5CJzprAx3ShE79+Af+sdFPP052gObVBUrRhUEYU1mHV39Hg9JxkZOu+HkghJTv1gVJyr1mwLiMgVFf9j3TVzsYkU4j7WqE+n00qrlFWWM3B7/1a5hDYU3lqwgbOnbXRSkCA5y3njS8RWtmJ8MeyjyxMy4nvmzapdrwjlWMNJpg8mfLifp94/u3/g0RRzsd7GBkol5fh6jYmmDPbsDZsUZpoalR5Card3IWBgu8iTWxjf603L+JQ5oU4t9B8ZevoWBQ7S7nCFfP+4QJkafNF2z/5jusn2CtsVb6XF0noMUheYGkeMPYqznhTzL66qO/FLlBIH9vOZiEBwEhDUfW1tyMiUtNGOZnVka6ZkJiUq9i02ifktVjqE= 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: >> -               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