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[2003:cb:c70d:1f00:7a4e:8f21:98db:baef]) by smtp.gmail.com with ESMTPSA id o12-20020a5d684c000000b0034aa1e534c2sm11277902wrw.96.2024.04.24.02.40.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Apr 2024 02:40:09 -0700 (PDT) Message-ID: Date: Wed, 24 Apr 2024 11:40:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 06/18] mm: make folio_mapcount() return 0 for small typed folios To: 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 , Yin Fengwei , 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> <20240409192301.907377-7-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-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 5A11540012 X-Stat-Signature: j6xqcwyqbbosbamdmmard4xz3ctzo5m5 X-Rspam-User: X-HE-Tag: 1713951615-266294 X-HE-Meta: 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 Z8WW3dS/ D33I5fcex3Yw2FlN5R8UQSxlbKidtRKVHhKNup3KVcDbYVlTrN3M49XyKqdm0BugNbjIuL7Yi3ICc7xnKuNS4jAyqbE6zB7ZiXnuS/t9qSPxbIETRIAINZDaUdWJ58L7aT9iZdt6smILa5YQtYg/+j5spCnH9eSpHzItLNLrWU8YtLWFMUmS0lPMLA8iOZOi73GoBYJ9s9poWRFJbS+vvsV0lB6DqAcH5WSYN5MjLTQm2Nrr7cOSzRwKlgCwNaC1YYEEA5/85abMJcCLr/neA5BjDQdJbTeDcLSjNVJk1hT78l7cFdHKjpMBCtd8zpRUCJou8YzIY+9RbOjVfp4G14TNEGtPIECMVdbI1mJr8tmYtd/1003q2mRXO0KRJgctEwN1YQi4FujdnZlSFiArK+ATMbg== 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 09.04.24 21:22, David Hildenbrand wrote: > We already handle it properly for large folios. Let's also return "0" > for small typed folios, like page_mapcount() currently would. > > Consequently, folio_mapcount() will never return negative values for > typed folios, but may return negative values for underflows. > > Signed-off-by: David Hildenbrand > --- > include/linux/mm.h | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index daf687f0e8e5..d453232bba62 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1260,12 +1260,19 @@ static inline int folio_large_mapcount(const struct folio *folio) > * references the entire folio counts exactly once, even when such special > * page table entries are comprised of multiple ordinary page table entries. > * > + * Will report 0 for pages which cannot be mapped into userspace, such as > + * slab, page tables and similar. > + * > * Return: The number of times this folio is mapped. > */ > static inline int folio_mapcount(const struct folio *folio) > { > - if (likely(!folio_test_large(folio))) > - return atomic_read(&folio->_mapcount) + 1; > + int mapcount; > + > + if (likely(!folio_test_large(folio))) { > + mapcount = atomic_read(&folio->_mapcount); > + return page_type_has_type(mapcount) ? 0 : mapcount + 1; > + } > return folio_large_mapcount(folio); > } > From 98acfb7ff35cb65fcfca5e799bf58f8afe84a645 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Wed, 24 Apr 2024 10:56:17 +0200 Subject: [PATCH] !fixup: mm: make folio_mapcount() return 0 for small typed folios Just like page_mapcount(), let's make folio_mapcount() slightly more efficient. Signed-off-by: David Hildenbrand --- include/linux/mm.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index cf700c5cdd58b..78e583b50e421 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1271,8 +1271,11 @@ static inline int folio_mapcount(const struct folio *folio) int mapcount; if (likely(!folio_test_large(folio))) { - mapcount = atomic_read(&folio->_mapcount); - return page_type_has_type(mapcount) ? 0 : mapcount + 1; + mapcount = atomic_read(&folio->_mapcount) + 1; + /* Handle page_has_type() pages */ + if (mapcount < PAGE_MAPCOUNT_RESERVE + 1) + mapcount = 0; + return mapcount; } return folio_large_mapcount(folio); } -- 2.44.0 -- Cheers, David / dhildenb