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Fri, 9 Apr 2021 04:37:49 +0000 Subject: Re: [PATCH 3/4] mm/hugeltb: fix potential wrong gbl_reserve value for hugetlb_acct_memory() To: Miaohe Lin , akpm@linux-foundation.org Cc: n-horiguchi@ah.jp.nec.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20210402093249.25137-1-linmiaohe@huawei.com> <20210402093249.25137-4-linmiaohe@huawei.com> <20afccd5-2bc4-9db9-695e-dd6175b0b42b@oracle.com> <1311fcfe-bc5f-e878-3912-ca9a9e0eed90@huawei.com> <0ebaa062-80e8-b380-c02e-7eb72e67f973@huawei.com> <90188b1a-a206-5586-2da9-683f7537f960@oracle.com> <8dfe32a3-1789-6a40-b650-304c2cfb6531@huawei.com> From: Mike Kravetz Message-ID: <83e5f2a0-bf92-ab42-c5ff-52a07eab9ee8@oracle.com> Date: Thu, 8 Apr 2021 21:37:46 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 In-Reply-To: <8dfe32a3-1789-6a40-b650-304c2cfb6531@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: CO2PR04CA0157.namprd04.prod.outlook.com (2603:10b6:104:4::11) 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 CO2PR04CA0157.namprd04.prod.outlook.com (2603:10b6:104:4::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4020.17 via Frontend Transport; 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identity=mailfrom; envelope-from=""; helo=aserp2120.oracle.com; client-ip=141.146.126.78 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617943080-788647 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 4/8/21 8:01 PM, Miaohe Lin wrote: > On 2021/4/9 6:53, Mike Kravetz wrote: >> >> Yes, add a comment to hugetlb_unreserve_pages saying that !resv_map >> implies freed == 0. >> > > Sounds good! > >> It would also be helpful to check for (chg - freed) == 0 and skip the >> calls to hugepage_subpool_put_pages() and hugetlb_acct_memory(). Both >> of those routines may perform an unnecessary lock/unlock cycle in this >> case. >> >> A simple >> if (chg == free) >> return 0; >> before the call to hugepage_subpool_put_pages would work. > > This may not be really helpful because hugepage_subpool_put_pages() and hugetlb_acct_memory() > both would handle delta == 0 case without unnecessary lock/unlock cycle. > Does this make sense for you? If so, I will prepare v2 with the changes to add a comment > to hugetlb_unreserve_pages() __without__ the check for (chg - freed) == 0. Sorry, I forgot about the recent changes to check for delta == 0. No need for the check here, just the comment. -- Mike Kravetz