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dkim=none (message not signed) header.d=none;linux-foundation.org; dmarc=none action=none header.from=oracle.com; Received: from BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) by BY5PR10MB4356.namprd10.prod.outlook.com (2603:10b6:a03:210::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3977.24; Wed, 24 Mar 2021 16:43:53 +0000 Received: from BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::980e:61ba:57d2:47ee]) by BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::980e:61ba:57d2:47ee%6]) with mapi id 15.20.3955.027; Wed, 24 Mar 2021 16:43:53 +0000 Subject: Re: [RFC PATCH 2/8] hugetlb: recompute min_count when dropping hugetlb_lock To: Michal Hocko Cc: Peter Zijlstra , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Shakeel Butt , Oscar Salvador , David Hildenbrand , Muchun Song , David Rientjes , Miaohe Lin , Matthew Wilcox , HORIGUCHI NAOYA , "Aneesh Kumar K . V" , Waiman Long , Peter Xu , Mina Almasry , Andrew Morton References: <20210319224209.150047-1-mike.kravetz@oracle.com> <20210319224209.150047-3-mike.kravetz@oracle.com> <52db15d1-4ed1-6c3c-b638-6efdccf6e62e@oracle.com> From: Mike Kravetz Message-ID: <7f1f3c92-725f-0cc9-3dc8-420c4e9c96ec@oracle.com> Date: Wed, 24 Mar 2021 09:43:51 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [50.38.35.18] X-ClientProxiedBy: MWHPR2001CA0001.namprd20.prod.outlook.com (2603:10b6:301:15::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 MWHPR2001CA0001.namprd20.prod.outlook.com (2603:10b6:301:15::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3977.26 via Frontend Transport; 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Then, drop the lock and free all >> pages on the list. If we do this, then the value computed here (min_count) >> can not change while we are looping. So, this patch would be unnecessary. >> That is another argument in favor of batching the frees. >> >> Unless there is something wrong in my thinking, I am going to take that >> approach and drop this patch. > > Makes sense > I still think this is the way to go in this series. However, Muchun's "Free some vmemmap pages of HugeTLB page" series would likely want to drop the lock for each page as the free operation may fail. So, we may end up back with one lock cycle per page. That is something that will be discussed in that series. -- Mike Kravetz