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[2003:cb:c713:2a00:f151:50f1:7164:32e6]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36d2716cab8sm2323080f8f.33.2024.08.08.08.56.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Aug 2024 08:56:46 -0700 (PDT) Message-ID: <7eca670c-1196-4e50-be26-3fa52fa93ad2@redhat.com> Date: Thu, 8 Aug 2024 17:56:44 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/4] mm: free zapped tail pages when splitting isolated thp To: Usama Arif , akpm@linux-foundation.org, linux-mm@kvack.org Cc: hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, roman.gushchin@linux.dev, yuzhao@google.com, baohua@kernel.org, ryan.roberts@arm.com, rppt@kernel.org, willy@infradead.org, cerasuolodomenico@gmail.com, corbet@lwn.net, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com, Shuang Zhai References: <20240807134732.3292797-1-usamaarif642@gmail.com> <20240807134732.3292797-2-usamaarif642@gmail.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 83B3280002 X-Stat-Signature: ud7u76rdjwbp18bj6c94ekwe41iwm5rm X-Rspam-User: X-HE-Tag: 1723132610-366748 X-HE-Meta: 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 0hWk+429 YiO95HLmTwpyXBDcHdVu99NyrDYrXpsV+ETgckF4dAs7P7sNDGsBQCO94+h036IrrgPoTP0r4MPpcFWHxdEGTQFtzQjWjc7Dg1glQu2tnIQ0YSbxrseAa0L7i2yH5L2cUmeXN7yXDSE9VWoqG8sgoMmZgTOlNZWDMnjyTtf+UqMFJFtxlzV80O/5803CFe+ItGHVv0b9iENI6vtcFAJlu77sXnjOMAcS8sUCaORYxGRw2e2ysaxPPLdWpqz+GhvxZovt4Vbpv+kyMG5ylQ5PFQypneBOaU0GJCg1GbVEALKt+4XvVMNZI/FfvuSe02DxI9VQCjHbiQb2wEttHyQiMwJYI5799PtHtFlQoCOU3BTC+Ay2qTQEBT6YfZsaR2V0py7gN4ynSU6ygvurniIN/7vEom05AlJn53pbA 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: On 07.08.24 15:46, Usama Arif wrote: > From: Yu Zhao > > If a tail page has only two references left, one inherited from the > isolation of its head and the other from lru_add_page_tail() which we > are about to drop, it means this tail page was concurrently zapped. > Then we can safely free it and save page reclaim or migration the > trouble of trying it. > > Signed-off-by: Yu Zhao > Tested-by: Shuang Zhai > Signed-off-by: Usama Arif > --- > mm/huge_memory.c | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 0167dc27e365..35c1089d8d61 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2923,7 +2923,9 @@ static void __split_huge_page(struct page *page, struct list_head *list, > unsigned int new_nr = 1 << new_order; > int order = folio_order(folio); > unsigned int nr = 1 << order; > + struct folio_batch free_folios; > > + folio_batch_init(&free_folios); > /* complete memcg works before add pages to LRU */ > split_page_memcg(head, order, new_order); > > @@ -3007,6 +3009,26 @@ static void __split_huge_page(struct page *page, struct list_head *list, > if (subpage == page) > continue; > folio_unlock(new_folio); > + /* > + * If a folio has only two references left, one inherited > + * from the isolation of its head and the other from > + * lru_add_page_tail() which we are about to drop, it means this > + * folio was concurrently zapped. Then we can safely free it > + * and save page reclaim or migration the trouble of trying it. > + */ > + if (list && page_ref_freeze(subpage, 2)) { > + VM_WARN_ON_ONCE_FOLIO(folio_test_lru(new_folio), new_folio); > + VM_WARN_ON_ONCE_FOLIO(folio_test_large(new_folio), new_folio); > + VM_WARN_ON_ONCE_FOLIO(folio_mapped(new_folio), new_folio); > + > + folio_clear_active(new_folio); > + folio_clear_unevictable(new_folio); > + if (folio_batch_add(&free_folios, folio) == 0) { nit: "!folio_batch_add(&free_folios, folio)" Nothing else jumped at me. -- Cheers, David / dhildenb