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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6e43ba368a9sm14778966d6.29.2025.02.07.01.06.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Feb 2025 01:06:45 -0800 (PST) Date: Fri, 7 Feb 2025 04:06:42 -0500 From: Gregory Price To: "Huang, Ying" Cc: SeongJae Park , Bharata B Rao , Raghavendra K T , linux-mm@kvack.org, akpm@linux-foundation.org, lsf-pc@lists.linux-foundation.org, nehagholkar@meta.com, abhishekd@meta.com, nphamcs@gmail.com, hannes@cmpxchg.org, feng.tang@intel.com, kbusch@meta.com, Hasan.Maruf@amd.com, david@redhat.com, willy@infradead.org, k.shutemov@gmail.com, mgorman@techsingularity.net, vbabka@suse.cz, hughd@google.com, rientjes@google.com, shy828301@gmail.com, liam.howlett@oracle.com, peterz@infradead.org, mingo@redhat.com, nadav.amit@gmail.com, shivankg@amd.com, ziy@nvidia.com, jhubbard@nvidia.com, AneeshKumar.KizhakeVeetil@arm.com, linux-kernel@vger.kernel.org, jon.grimm@amd.com, santosh.shukla@amd.com, Michael.Day@amd.com, riel@surriel.com, weixugc@google.com, leesuyeon0506@gmail.com, honggyu.kim@sk.com, leillc@google.com, kmanaouil.dev@gmail.com, rppt@kernel.org, dave.hansen@intel.com Subject: Re: [LSF/MM/BPF TOPIC] Overhauling hot page detection and promotion based on PTE A bit scanning Message-ID: References: <20250127183403.67757-1-sj@kernel.org> <87ikpmgooo.fsf@DESKTOP-5N7EMDA> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ikpmgooo.fsf@DESKTOP-5N7EMDA> On Fri, Feb 07, 2025 at 04:10:47PM +0800, Huang, Ying wrote: > SeongJae Park writes: > > > > I agree the fairness is a thing that we need to aware of. But IMHO, it is > > something that the async approach can further be advanced for, not a strict > > blocker for now. > > Personally, I have no objection to async operations in general. > However, we may need to find some way to control these async operations > instead of adding more and more background kthreads blindly. How to > charge and constrain the resources used by these async operations is > important too. For example, some users may want to bind some async > operations on some CPUs. > > IMHO, we should think about the requirements and possible solutions > instead of ignoring the issues. > It also concerns me that most every proposal on async promotion ignores the promotion-node selection problem as if it's a secondary issue. Async systems fundamentally lack accessor-locality information unless it is recorded - and recording this information is expensive and/or heuristically imprecise for memory shared across tasks (two threads in the same process schedule across sockets). If we can't agree on a solution to this problem, it undercuts many of these RFCs which often simply hard-code the target node to "0" because it's too hard or too expensive to consider the multi-socket scenario. ~Gregory