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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 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 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 Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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