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[2003:cb:c716:f300:c9f0:f643:6aa2:16]) by smtp.gmail.com with ESMTPSA id e5-20020adfe385000000b003455e5d2569sm4015124wrm.0.2024.04.19.02.19.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 19 Apr 2024 02:19:50 -0700 (PDT) Message-ID: <7a8eb8c0-35e5-4f45-bdd5-11a775ae752d@redhat.com> Date: Fri, 19 Apr 2024 11:19:49 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 05/18] mm: improve folio_likely_mapped_shared() using the mapcount of large folios To: "Yin, Fengwei" , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-doc@vger.kernel.org, cgroups@vger.kernel.org, linux-sh@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , "Matthew Wilcox (Oracle)" , Peter Xu , Ryan Roberts , Yang Shi , Zi Yan , Jonathan Corbet , Hugh Dickins , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , Chris Zankel , Max Filippov , Muchun Song , Miaohe Lin , Naoya Horiguchi , Richard Chang References: <20240409192301.907377-1-david@redhat.com> <20240409192301.907377-6-david@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: F158212000F X-Stat-Signature: po1ntcssr88e6uydbxfzxekrnijw8j1g X-HE-Tag: 1713518394-632530 X-HE-Meta: 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 hqB72O4J bHQMbGtlIBldZxeElo3QgfLEkfHt4qyPVFSEUCja6GFKV2gs2G4+qW6U2UotsMVHxNiu9uIgxBPFQPxVl9KgbbplPZkZZ/dfBLWwT7WbhtrBC3VnaKJ4sQ/wCsA== 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 19.04.24 04:29, Yin, Fengwei wrote: > > > On 4/10/2024 3:22 AM, David Hildenbrand wrote: >> @@ -2200,7 +2200,22 @@ static inline size_t folio_size(struct folio *folio) >> */ >> static inline bool folio_likely_mapped_shared(struct folio *folio) >> { >> - return page_mapcount(folio_page(folio, 0)) > 1; >> + int mapcount = folio_mapcount(folio); >> + >> + /* Only partially-mappable folios require more care. */ >> + if (!folio_test_large(folio) || unlikely(folio_test_hugetlb(folio))) >> + return mapcount > 1; > My understanding is that mapcount > folio_nr_pages(folio) can cover > order 0 folio. And also folio_entire_mapcount() can cover hugetlb (I am > not 100% sure for this one). I am wondering whether we can drop above > two lines? Thanks. folio_entire_mapcount() does not apply to small folios, so we must not call that for small folios. Regarding hugetlb, subpage mapcounts are completely unused, except subpage 0 mapcount, which is now *always* negative (storing a page type) -- so there is no trusting on that value at all. So in the end, it all looked cleanest when only special-casing on partially-mappable folios where we know the entire mapcount exists and we know that subapge mapcount 0 actually stores something reasonable (not a type). Thanks! -- Cheers, David / dhildenb