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[2003:d8:2f37:2b00:948c:dd9f:29c8:73f4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b7e8ab093sm150530455e9.22.2025.09.01.01.06.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 01 Sep 2025 01:06:25 -0700 (PDT) Message-ID: <1431a00b-d68c-4f25-b075-5021e2faa9db@redhat.com> Date: Mon, 1 Sep 2025 10:06:23 +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 4/7] mm: Revert "mm/gup: clear the LRU flag of a page before adding to LRU batch" To: Hugh Dickins , Andrew Morton Cc: Will Deacon , Shivank Garg , Matthew Wilcox , Christoph Hellwig , Keir Fraser , Jason Gunthorpe , John Hubbard , Frederick Mayle , Peter Xu , "Aneesh Kumar K.V" , Johannes Weiner , Vlastimil Babka , Alexander Krabler , Ge Yang , Li Zhe , Chris Li , Yu Zhao , Axel Rasmussen , Yuanchu Xie , Wei Xu , Konstantin Khlebnikov , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <0215a42b-99cd-612a-95f7-56f8251d99ef@google.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 31.08.25 11:11, Hugh Dickins wrote: > This reverts commit 33dfe9204f29b415bbc0abb1a50642d1ba94f5e9: > now that collect_longterm_unpinnable_folios() is checking ref_count > instead of lru, and mlock/munlock do not participate in the revised > LRU flag clearing, those changes are misleading, and enlarge the > window during which mlock/munlock may miss an mlock_count update. > > It is possible (I'd hesitate to claim probable) that the greater > likelihood of missed mlock_count updates would explain the "Realtime > threads delayed due to kcompactd0" observed on 6.12 in the Link below. > If that is the case, this reversion will help; but a complete solution > needs also a further patch, beyond the scope of this series. > > Included some 80-column cleanup around folio_batch_add_and_move(). > > The role of folio_test_clear_lru() (before taking per-memcg lru_lock) > is questionable since 6.13 removed mem_cgroup_move_account() etc; but > perhaps there are still some races which need it - not examined here. > > Link: https://lore.kernel.org/linux-mm/DU0PR01MB10385345F7153F334100981888259A@DU0PR01MB10385.eurprd01.prod.exchangelabs.com/ > Signed-off-by: Hugh Dickins > Cc: > --- Acked-by: David Hildenbrand -- Cheers David / dhildenb