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Wed, 17 Mar 2021 00:28:22 +0000 Subject: Re: [PATCH v2 5/5] mm/hugetlb: avoid calculating fault_mutex_hash in truncate_op case To: Miaohe Lin , akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20210316022758.52993-1-linmiaohe@huawei.com> <4b3e9ea6-69e3-493c-342e-92117f274e06@huawei.com> From: Mike Kravetz Message-ID: <952e9130-a084-20a7-aa7c-486fe9ccc8c6@oracle.com> Date: Tue, 16 Mar 2021 17:27:45 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 In-Reply-To: <4b3e9ea6-69e3-493c-342e-92117f274e06@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [50.38.35.18] X-ClientProxiedBy: MW4PR04CA0012.namprd04.prod.outlook.com (2603:10b6:303:69::17) To BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.2.112] (50.38.35.18) by MW4PR04CA0012.namprd04.prod.outlook.com (2603:10b6:303:69::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3955.18 via Frontend Transport; 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identity=mailfrom; envelope-from=""; helo=aserp2130.oracle.com; client-ip=141.146.126.79 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615940914-626711 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 3/15/21 11:49 PM, Miaohe Lin wrote: > On 2021/3/16 11:07, Mike Kravetz wrote: >> On 3/15/21 7:27 PM, Miaohe Lin wrote: >>> The fault_mutex hashing overhead can be avoided in truncate_op case >>> because page faults can not race with truncation in this routine. So >>> calculate hash for fault_mutex only in !truncate_op case to save some cpu >>> cycles. >>> >>> Reviewed-by: Mike Kravetz >>> Signed-off-by: Miaohe Lin >>> Cc: Mike Kravetz >>> --- >>> v1->v2: >>> remove unnecessary initialization for variable hash >>> collect Reviewed-by tag from Mike Kravetz >> >> My apologies for not replying sooner and any misunderstanding from my >> previous comments. >> > > That's all right. > >> If the compiler is going to produce a warning because the variable is >> not initialized, then we will need to keep the initialization. >> Otherwise, this will show up as a build regression. Ideally, there >> would be a modifier which could be used to tell the compiler the >> variable will used. I do not know if such a modifier exists. >> > > I do not know if such a modifier exists too. But maybe not all compilers are intelligent > enough to not produce a warning. It would be safe to keep the initialization... > >> The patch can not produce a new warning. So, if you need to initialize > > So just drop this version of the patch? Or should I send a new version with your Reviewed-by tag and > keep the initialization? > Yes, drop this version of the patch. You can add my Reviewed-by to the previous version that included the initialization and resend. All the cleanup patches in this series should be good to go. -- Mike Kravetz