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Wed, 05 Feb 2025 19:14:59 -0800 (PST) MIME-Version: 1.0 References: <20250123105721.424117-1-raghavendra.kt@amd.com> <0a9914f8-bec7-4e58-ab12-a87fe3876187@sk.com> In-Reply-To: <0a9914f8-bec7-4e58-ab12-a87fe3876187@sk.com> From: Yuanchu Xie Date: Wed, 5 Feb 2025 19:14:42 -0800 X-Gm-Features: AWEUYZn6MPTY1_MU1S8hLVyAdHYXGxJzF-tVdC8MWzr1l3c8Snt-2ud2DsTxV0U Message-ID: Subject: Re: [LSF/MM/BPF TOPIC] Overhauling hot page detection and promotion based on PTE A bit scanning To: Hyeonggon Yoo , Raghavendra K T , "bharata@amd.com" Cc: "linux-mm@kvack.org" , "akpm@linux-foundation.org" , "lsf-pc@lists.linux-foundation.org" , kernel_team@skhynix.com, 42.hyeyoo@gmail.com, "gourry@gourry.net" , "nehagholkar@meta.com" , "abhishekd@meta.com" , "ying.huang@linux.alibaba.com" , "nphamcs@gmail.com" , "hannes@cmpxchg.org" , "feng.tang@intel.com" , "kbusch@meta.com" , "Hasan.Maruf@amd.com" , "sj@kernel.org" , "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" , Kinsey Ho Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 9BACE40006 X-Stat-Signature: 55jp1gqscqajh3fb385ybn4s4tsgajbf X-Rspam-User: X-HE-Tag: 1738811700-698611 X-HE-Meta: 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 mtXxdci/ BXZrDPA9V9c7RKa6+7jFGN3zqAt0wtCMjJgAWZ2J7yIjsJhIeobaXvEj84U3UyT+cUqszCjG0wJ1VXq6/rvQWRna6yXk8t337n3GVNWIAGFG1wQznGIS1HUGbvluXfMs4cpl1wjEkZejMuaJ17b+p6d8HxppdPoAD3oX6pdnK2tjQP5oW70WGlbVO3fEFgc0Rnvu0LIP6gnD3Qs7BFwKfZVLxgmQ/uXgnFY7vIUYydgT+tQJd0fDLpmqUfdrx+xLu4+l7Sezt4LvVgyDzyUaY+CE7lhy8Loww5Pusd6N/vIsPYrRarnCyzGMv38FE/FjAoz4wJ9epxHHs8El/X3RV2eFL9/fD7ExyAs6YCXS2fR6NC2m8yy06DB43lnjBcX2V81hY9CR/2f9SNW8= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000029, 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 Thu, Jan 23, 2025 at 9:53=E2=80=AFPM Hyeonggon Yoo wrote: > On 1/23/2025 7:57 PM, Raghavendra K T wrote: > > Bharata and I would like to propose the following topic for LSFMM. > > > > Here is the list of potential discussion points: > > 1. Other improvements and enhancements to PTE A bit scanning approach. = Use of > > multiple kernel threads, throttling improvements, promotion policies, p= er-process > > opt-in via prctl, virtual vs physical address based scanning, tuning ho= t page > > detection algorithm etc. > > Yuanchu's MGLRU periodic aging series [1] seems quite relevant here, > you might want to look at it. adding Yuanchu to Cc. Thanks for the mention, Hyeonggon Yoo. Working set reporting doesn't aim to promote/demote/reclaim pages, but to show aggregate stats of the memory in access recency. The periodic aging part is optional since client devices wouldn't want a background daemon wasting battery aging lruvecs when nothing is happening. For the server use case, the aging kthread periodically invoke MGLRU aging, which performs the PTE A bit scanning. MGLRU handles unmapped page cache as well for reclaim purposes. Reading through the kmmscand patch series. Kmmscand also keeps a list of mm_struct and performs scanning on them, so given there're many use cases for PTE A bit scanning, this seems like an opportunity to abstract some of the mm_struct scanning. Code-wise the A bit scanners do very similar things, and the MGLRU version has optional optimizations that reduce the scanning overhead. I wonder if you have considered migrating pages from the MGLRU young generation of a remote node, or pages that have remained in the young generation. Some changes to MGLRU would be necessary in that case. Also adding Kinsey Ho since he's been looking at page promotion as well. Thanks, Yuanchu