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Mon, 12 Apr 2021 18:28:42 +0000 Subject: Re: [PATCH v2 3/5] mm/hugeltb: clarify (chg - freed) won't go negative in hugetlb_unreserve_pages() To: Miaohe Lin , akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linfeilong@huawei.com References: <20210410072348.20437-1-linmiaohe@huawei.com> <20210410072348.20437-4-linmiaohe@huawei.com> From: Mike Kravetz Message-ID: <23a4924a-2881-3c5e-b70e-ece65a0cb7ca@oracle.com> Date: Mon, 12 Apr 2021 11:28:41 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 In-Reply-To: <20210410072348.20437-4-linmiaohe@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: MWHPR02CA0013.namprd02.prod.outlook.com (2603:10b6:300:4b::23) 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 MWHPR02CA0013.namprd02.prod.outlook.com (2603:10b6:300:4b::23) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4020.16 via Frontend Transport; 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identity=mailfrom; envelope-from=""; helo=userp2130.oracle.com; client-ip=156.151.31.86 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618252131-338908 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 4/10/21 12:23 AM, Miaohe Lin wrote: > The resv_map could be NULL since this routine can be called in the evict > inode path for all hugetlbfs inodes and we will have chg = 0 in this case. > But (chg - freed) won't go negative as Mike pointed out: > > "If resv_map is NULL, then no hugetlb pages can be allocated/associated > with the file. As a result, remove_inode_hugepages will never find any > huge pages associated with the inode and the passed value 'freed' will > always be zero." > > Add a comment clarifying this to make it clear and also avoid confusion. > > Signed-off-by: Miaohe Lin Thanks, Reviewed-by: Mike Kravetz -- Mike Kravetz