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Sun, 06 Aug 2023 19:21:38 -0700 (PDT) Received: from [10.70.252.135] ([203.208.167.146]) by smtp.gmail.com with ESMTPSA id e6-20020a170902cf4600b001ac5896e96esm5514361plg.207.2023.08.06.19.21.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 06 Aug 2023 19:21:37 -0700 (PDT) Message-ID: <3403e5d3-e840-cea7-1863-b6b9ab7ecae0@bytedance.com> Date: Mon, 7 Aug 2023 10:21:20 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH v3 10/13] mm/khugepaged: collapse_pte_mapped_thp() with mmap_read_lock() Content-Language: en-US To: Hugh Dickins Cc: Andrew Morton , Pasha Tatashin , Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , Matthew Wilcox , David Hildenbrand , Suren Baghdasaryan , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Lorenzo Stoakes , Huang Ying , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , Russell King , "David S. Miller" , Michael Ellerman , "Aneesh Kumar K.V" , Heiko Carstens , Christian Borntraeger , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Vasily Gorbik , Jann Horn , Vishal Moola , Vlastimil Babka , Zi Yan , linux-arm-kernel@lists.infradead.org, sparclinux@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <7cd843a9-aa80-14f-5eb2-33427363c20@google.com> <0df84f9f-e9b0-80b1-4c9e-95abc1a73a96@bytedance.com> <884f20fe-d642-3a5f-522a-d756c3443bb4@google.com> From: Qi Zheng In-Reply-To: <884f20fe-d642-3a5f-522a-d756c3443bb4@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 4D01AC0009 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 59ynqmhk4mxuaqn1pnnfwbpyuuid6jfq X-HE-Tag: 1691374900-954688 X-HE-Meta: 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 CT1JW3Y/ 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 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: On 2023/8/6 11:55, Hugh Dickins wrote: > On Thu, 3 Aug 2023, Qi Zheng wrote: >> On 2023/7/12 12:42, Hugh Dickins wrote: >>> Bring collapse_and_free_pmd() back into collapse_pte_mapped_thp(). >>> It does need mmap_read_lock(), but it does not need mmap_write_lock(), >>> nor vma_start_write() nor i_mmap lock nor anon_vma lock. All racing >>> paths are relying on pte_offset_map_lock() and pmd_lock(), so use those. > ... >>> @@ -1681,47 +1634,76 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, >>> unsigned long addr, >>> >>> if (pte_none(ptent)) >>> continue; >>> - page = vm_normal_page(vma, addr, ptent); >>> - if (WARN_ON_ONCE(page && is_zone_device_page(page))) >>> + /* >>> + * We dropped ptl after the first scan, to do the >>> mmu_notifier: >>> + * page lock stops more PTEs of the hpage being faulted in, >>> but >>> + * does not stop write faults COWing anon copies from existing >>> + * PTEs; and does not stop those being swapped out or >>> migrated. >>> + */ >>> + if (!pte_present(ptent)) { >>> + result = SCAN_PTE_NON_PRESENT; >>> goto abort; >>> + } >>> + page = vm_normal_page(vma, addr, ptent); >>> + if (hpage + i != page) >>> + goto abort; >>> + >>> + /* >>> + * Must clear entry, or a racing truncate may re-remove it. >>> + * TLB flush can be left until pmdp_collapse_flush() does it. >>> + * PTE dirty? Shmem page is already dirty; file is read-only. >>> + */ >>> + pte_clear(mm, addr, pte); >> >> This is not non-present PTE entry, so we should call ptep_clear() to let >> page_table_check track the PTE clearing operation, right? Otherwise it >> may lead to false positives? > > You are right: thanks a lot for catching that: fix patch follows. With fix patch: Reviewed-by: Qi Zheng Thanks. > > Hugh