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X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [RFC PATCH] mm: support large folio numa balancing Content-Language: en-US To: Baolin Wang , Kefeng Wang , David Hildenbrand , akpm@linux-foundation.org Cc: ying.huang@intel.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <606d2d7a-d937-4ffe-a6f2-dfe3ae5a0c91@redhat.com> <70973a55-63a0-4a85-abe5-d8681fdb3886@huawei.com> From: John Hubbard In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MN2PR01CA0015.prod.exchangelabs.com (2603:10b6:208:10c::28) To BY5PR12MB4130.namprd12.prod.outlook.com (2603:10b6:a03:20b::16) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BY5PR12MB4130:EE_|DM6PR12MB4057:EE_ X-MS-Office365-Filtering-Correlation-Id: 3e42517d-f4f1-4d45-8e74-08dbe4960525 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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9Rf0Nv9p8r56R9A7lo6xbq72RyF8QrXO3kM+j2PHPdU2G2hOLQqGqR6VLhZiCdikurcrazkPFm2Vhj+5nBz3aDy/iLpGTGaADDQpaTCpQznC8FB7oJZDkbeLNkmAjwfrJXdv7zqYgyM7T8rXcLCbmqGZYzfFPmuEYlwDOvYWvjfQDNuNdXRZOeBJR21uJ45lhyZAfJBkyzoYhcfya49bM35zDUdPHGFBPSFVQSRnGIWGp1Rc= 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: List-Subscribe: List-Unsubscribe: On 11/13/23 5:01 AM, Baolin Wang wrote: > > > On 11/13/2023 8:10 PM, Kefeng Wang wrote: >> >> >> On 2023/11/13 18:53, David Hildenbrand wrote: >>> On 13.11.23 11:45, Baolin Wang wrote: >>>> Currently, the file pages already support large folio, and >>>> supporting for >>>> anonymous pages is also under discussion[1]. Moreover, the numa >>>> balancing >>>> code are converted to use a folio by previous thread[2], and the >>>> migrate_pages >>>> function also already supports the large folio migration. >>>> >>>> So now I did not see any reason to continue restricting NUMA >>>> balancing for >>>> large folio. >>> >>> I recall John wanted to look into that. CCing him. >>> >>> I'll note that the "head page mapcount" heuristic to detect sharers will >>> now strike on the PTE path and make us believe that a large folios is >>> exclusive, although it isn't. >>> >>> As spelled out in the commit you are referencing: >>> >>> commit 6695cf68b15c215d33b8add64c33e01e3cbe236c >>> Author: Kefeng Wang >>> Date:   Thu Sep 21 15:44:14 2023 +0800 >>> >>>      mm: memory: use a folio in do_numa_page() >>>      Numa balancing only try to migrate non-compound page in >>> do_numa_page(), >>>      use a folio in it to save several compound_head calls, note we use >>>      folio_estimated_sharers(), it is enough to check the folio >>> sharers since >>>      only normal page is handled, if large folio numa balancing is >>> supported, a >>>      precise folio sharers check would be used, no functional change >>> intended. >>> >>> >>> I'll send WIP patches for one approach that can improve the situation >>> soonish. To be honest, I'm still catching up on the approximate vs. exact sharers case. It wasn't clear to me why a precise sharers count is needed in order to do this. Perhaps the cost of making a wrong decision is considered just too high? >> >> When convert numa balance to use folio, I make similar change, it works >> with large anon folio(test with v5), but David's precise folio sharers >> should be merged firstly, also if a large folio shared by many process, >> we maybe split it, don't sure about it, this need some evaluation. > > IIUC, numa balancing will not split the large folio. That matches my reading of the code: normal (PMD-based) THPs are split, but the code does not yet split PTE-THPs (also known as small-size THPs). thanks, -- John Hubbard NVIDIA