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Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1r3vr6-007DDR-00; Fri, 17 Nov 2023 10:13:44 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id A635C300478; Fri, 17 Nov 2023 11:13:43 +0100 (CET) Date: Fri, 17 Nov 2023 11:13:43 +0100 From: Peter Zijlstra To: Mel Gorman Cc: "Huang, Ying" , Baolin Wang , David Hildenbrand , akpm@linux-foundation.org, wangkefeng.wang@huawei.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, John Hubbard Subject: Re: [RFC PATCH] mm: support large folio numa balancing Message-ID: <20231117101343.GH3818@noisy.programming.kicks-ass.net> References: <606d2d7a-d937-4ffe-a6f2-dfe3ae5a0c91@redhat.com> <871qctf89m.fsf@yhuang6-desk2.ccr.corp.intel.com> <87sf57en8n.fsf@yhuang6-desk2.ccr.corp.intel.com> <20231117100745.fnpijbk4xgmals3k@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231117100745.fnpijbk4xgmals3k@techsingularity.net> X-Rspamd-Queue-Id: 832504000C X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: qmc31iu3fsgbs38kmin179tqxra7d5cf X-HE-Tag: 1700216041-237420 X-HE-Meta: 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 rvcDPXnY kkFF0uMbHlLvvzqrW0/PIMLiC8+Tf6najnX+QItDBc6AeFyBwfje5Jo3nxv/g7G93efmIsiIwPWRvXZHJayuULTbACufebqFc89NfIujAJSpJLodLCqZlyiUiI5lkUy4Q1hnBseIaDjZvtVY= 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 Fri, Nov 17, 2023 at 10:07:45AM +0000, Mel Gorman wrote: > This leads into a generic problem with large anything with NUMA > balancing -- false sharing. As it stands, THP can be false shared by > threads if thread-local data is split within a THP range. In this case, > the ideal would be the THP is migrated to the hottest node but such > support doesn't exist. The same applies for folios. If not handled > properly, a large folio of any type can ping-pong between nodes so just > migrating because we can is not necessarily a good idea. The patch > should cover a realistic case why this matters, why splitting the folio > is not better and supporting data. Would it make sense to have THP merging conditional on all (most?) pages having the same node?