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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) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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?