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([2605:59c8:829:4c00:82ee:73ff:fe41:9a02]) by smtp.googlemail.com with ESMTPSA id d9443c01a7336-1fed7f1cb56sm122592975ad.201.2024.07.31.10.02.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 31 Jul 2024 10:02:23 -0700 (PDT) Message-ID: <17ae2088c08d34a17db8eeb1fa2821d686198a5b.camel@gmail.com> Subject: Re: [RFC v11 08/14] mm: page_frag: some minor refactoring before adding new API From: Alexander H Duyck To: Yunsheng Lin Cc: davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , linux-mm@kvack.org Date: Wed, 31 Jul 2024 10:02:22 -0700 In-Reply-To: References: <20240719093338.55117-1-linyunsheng@huawei.com> <20240719093338.55117-9-linyunsheng@huawei.com> <5a0e12c1-0e98-426a-ab4d-50de2b09f36f@huawei.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.48.4 (3.48.4-1.fc38) MIME-Version: 1.0 X-Stat-Signature: wc9awakprcnogcjkpbc8hreg4sdxxyfx X-Rspam-User: X-Rspamd-Queue-Id: 0BAAB1C003C X-Rspamd-Server: rspam02 X-HE-Tag: 1722445345-242565 X-HE-Meta: U2FsdGVkX19ig3rScJINe1X63G3Qh8Wemwj5TIMZ9rI9uRcCWsI658nttEkR5UCBRZUEM9KHZoS4RZiVOnUeDDEJfzExvpoUQGTxDNemwZNAvDYguSga8zjE7gB0a3i/wF+isiEcTzxFFcknlz7tndiPBBMx0MHRn8g97OkmJhKgU1jUMd+K6aE0v283/l9kdlTOfjjP4GUAetPZUb4bI5VczuD2oYCXOhG57Ct/cS/fMugVY1OzwCczuZH181hICx383cgjWuVjbBV6HufCETXxRzMjznISchycm0wXdEskm7lx4nURZSRjRjnoIMQcI7xDSAgZvrQIEA6+r200Ku0fUqt/sJ7qidTF1j2p0n2JIkgxMxvVzUDJY5V1mscDVvzm7fqbAWp2/ewr/Wu2V3Czgw1sV3wFtZL/kBTw9dB6QxHCdiE9cuN+W4ZuFH07fxkAoUv1CdnyT8ontahSGkuuufRvauAwTF4Sqe23eI8tei4R5QrqEdspdh1pQ8cKX3FaJcgR8pOoCwCkP6v0su9YxQdBOhwJ7MJRKno2DaxmpiKxdWsE81MI+1ExcY4bcz8dURj2brAxuRTcBEdKT2hwM2n6o6owfBDYfezLJytnbFk5PKiGsJR16oquCV5Up9HIe2D5MGlu+3jjpP7RE47IYUjcWhCE/Op5S7r+T06dT+630/jMFJ3R6tYOVFJ5oZAXAu+XRaldx+RJ260pweuK+8HW/nS5VV/LdPjnf6xFLe/J8rx26jowMQV2KONcgcv3GyOLI1v+kJtZ2X8gkNKr/ZOpCUjW3z2dNtXn/smo3kmSzct2T/sSrPwF1MALwv50TrADwo5vnxeeIkjeCHu0AZEpRe7cOp+KJ1mmqJnsYtCgyys3+Bt4G5pBQofEp4YMAoiwCmbdqMOM8DNJ8UCODeVudf9MM/Hl7ROnqde0+3oB6BeAj6kuvNQi/5zWPmzBZdBvFg89TazCeH3 w2KuqG6r AA+hXehe/FBlK8vAtSdzxLGnvmwbRlSq6Qp83ZGiqHpun2J5TZwALXYKp8BEiC1bNSC5z3ML9Ug/f/PGK7btqcKY0uRslm0HU5x8osMTszntFyd78kP5V63Iw0ETfAg+2FvwSgi4aKBbhYV9z8dTtN7LagjQC+4p3Jfdwnky5+sqGEzTw6MG0IXE4Byg3BSq2NMvKBT1as3E/EWrtORg3rwDsbDryMyy4nOeYP8/OlwatdbrQfwdYgma4Vf7cNuSsGXeU139O+tZl0v4ou+ruoRIEiZ/xb9xJEZpfZrzyZDqgQPnndtvOCSTeK/FPtEYulboKVZnz0s11Ksym55DNoe6jFDVuyk8zYr4eMsrQWs6M8Q813K9DXGVQgK4ttdPiATQydrYbpikzvBBlsWOSvdj5FI8xkNwPeohXydrDU2EJZ3g= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000006, 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 Wed, 2024-07-31 at 20:35 +0800, Yunsheng Lin wrote: > On 2024/7/30 23:12, Alexander H Duyck wrote: >=20 > ... >=20 > > > } > > >=20 > > > nc->pagecnt_bias--; > > > nc->remaining =3D remaining - fragsz; > > >=20 > > > return encoded_page_address(encoded_va) + > > > (page_frag_cache_page_size(encoded_va) - remaining); > >=20 > > Parenthesis here shouldn't be needed, addition and subtractions > > operations can happen in any order with the result coming out the same. >=20 > I am playing safe to avoid overflow here, as I am not sure if the allocat= or > will give us the last page. For example, '0xfffffffffffff000 + 0x1000' wi= ll > have a overflow. So what if it does though? When you subtract remaining it will underflow and go back to the correct value shouldn't it?