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[2003:cb:c705:4c00:486:38e2:8ff8:a135]) by smtp.gmail.com with ESMTPSA id o3-20020a05600c4fc300b003db1d9553e7sm3282961wmq.32.2023.01.25.13.29.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 Jan 2023 13:29:32 -0800 (PST) Message-ID: <53d86764-d155-8d97-1a4d-7e701848c950@redhat.com> Date: Wed, 25 Jan 2023 22:29:31 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH mm-unstable v2 1/6] mm: Add folio_estimated_mapcount() From: David Hildenbrand To: "Vishal Moola (Oracle)" , linux-mm@kvack.org Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org References: <20230124012210.13963-1-vishal.moola@gmail.com> <20230124012210.13963-2-vishal.moola@gmail.com> <477bbc1e-a60a-cfce-d31e-0b4bdd5f6429@redhat.com> <526e5156-6c4b-9f2c-1637-2f83c1dfea1e@redhat.com> Organization: Red Hat In-Reply-To: <526e5156-6c4b-9f2c-1637-2f83c1dfea1e@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E17E54000D X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: bqhbe1aakcoeix5g3cqnyqzu3i4kjow1 X-HE-Tag: 1674682176-469273 X-HE-Meta: U2FsdGVkX19OEoW3U18/uALizYg5Q+XW1TL8XojnWjEvknrlx+9VS7Ul4oCOh04Vaymk+ndFRNVX4mUCtEVzjqg8nIt+RYLPTqSbFkkzW881XY7YUxCYimqexZkyAnRMZ2kKItn++osERbGMBQon2dUYld4pxG4XU3+0x6ptaKa6o9QMF5UxIQ54xarVJRw6JBG7+SWGpALphQfJL2k5mYSftTrLbjZGflSkSRcz3tjpo35ey2DbF9GAjF8O2CB8T0K1XXbPm6Fd+zGcZI0rS1IEvVOCuyukiy6g73utKaem8c+TNnEktvHn8wIP+X/cSuBN3C4x/SWfVt62fKvqnokthKwPL79dlbq+3ul7yIIE46Q8gr8LdAExsNbL1J0QM9P/SBD5F6BySu9eJH6MES284vBU8mSo3x6BIvcGhKi+Jx2U0Cl8tcm4TeVw53IMAM2zbRdIOpfHSsy87tUXcnmIOKlqubv/yaUjGb8hQdJi8++N5+ScvOVreHRn0qGAcigbcQL0r6IX0zyBVUAaawyJmxKVIO/STd7nMywwnLEY3Vhg7Dtow/rVvF2cSomujkrqtdizr1+7XySmuXSnUoLrF4Cx+6ZE5ltYYAoMVwdxz66QO6Yj886hoVq9nMOPwnp3ogb67UKVSp9Pik8ciTYEFmHBga+nVbkI4Ym7Nicv2x6wXdZ3dD/J30bLJoRh/FkuT7R6Yn4puOBun4rvEu6p+GFl8pqriPMXWnSnR0h1ucDgUHe+hWcAPt2SAftd4r8UOGQ4dQzp0rkq3iCy7rwjxjjriFCkEdW/87Ifpak2USqBrzJMXAKn2Ixakbw91dLi9Y/gn0t+ZwFvZwnifvK/knkvTmulFqoB8IV74iEKwtae2sDRxhCdfWLqgAV1bs8WhpwvT++njkIL2DYEVAk6q70Kyz5fpV9kj46QTGFLZI6nokBXFBHEytbvsWhlkE9En90WCXMLg0R+iwi gfL7EOz8 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 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: On 25.01.23 11:24, David Hildenbrand wrote: > On 25.01.23 11:20, David Hildenbrand wrote: >> On 24.01.23 02:22, Vishal Moola (Oracle) wrote: >>> folio_estimated_mapcount() takes in a folio and calls page_mapcount() on >>> the first page of that folio. >>> >>> This is necessary for folio conversions where we only care about either the >>> entire_mapcount of a large folio, or the mapcount of a not large folio. >>> >>> This is in contrast to folio_mapcount() which calculates the total >>> number of the times a folio and its subpages are mapped. >>> >>> Signed-off-by: Vishal Moola (Oracle) >>> --- >>> include/linux/mm.h | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>> index c9db257f09b3..543c360f7ecc 100644 >>> --- a/include/linux/mm.h >>> +++ b/include/linux/mm.h >>> @@ -875,6 +875,11 @@ static inline int page_mapcount(struct page *page) >>> return mapcount; >>> } >>> >>> +static inline int folio_estimated_mapcount(struct folio *folio) >>> +{ >>> + return page_mapcount(folio_page(folio, 0)); >>> +} >>> + >>> int folio_total_mapcount(struct folio *folio); >>> >>> /** >> >> I'm sorry, but "estimated" as absolutely unclear semantics. You could >> have a THP mapped into 9999 processes using THP and the estimation would >> be "0". > > ... or would it be 9999 ? What about a PMD-mapped THP? What about a > partially unmapped THP? > > What are we estimating? Thinking about mapcounts again, might not have been my smartest moment. What we return here is the precise number of times the first subpage is mapped (via the large folio and directly). That's supposed to be an estimate for the number of times any subpage part of the folio is mapped. I really don't know a better name, but folio_estimated_mapcount() does not feel completely right to me and triggere dmy confusion in the first place ... hm ... -- Thanks, David / dhildenb