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dave.hansen@intel.com, gourry@gourry.net, hannes@cmpxchg.org, mgorman@techsingularity.net, mingo@redhat.com, peterz@infradead.org, raghavendra.kt@amd.com, riel@surriel.com, rientjes@google.com, sj@kernel.org, weixugc@google.com, willy@infradead.org, ying.huang@linux.alibaba.com, dave@stgolabs.net, nifan.cxl@gmail.com, joshua.hahnjy@gmail.com, xuezhengchu@huawei.com, yiannis@zptcorp.com, akpm@linux-foundation.org Subject: Re: [RFC PATCH v0 2/2] mm: sched: Batch-migrate misplaced pages Date: Thu, 22 May 2025 13:30:06 -0400 X-Mailer: MailMate (2.0r6255) Message-ID: In-Reply-To: <382839fc-ea63-421a-8397-72cb35dd8052@redhat.com> References: <20250521080238.209678-1-bharata@amd.com> <20250521080238.209678-3-bharata@amd.com> <62cef618-123c-4ffa-b45a-c38b65d2a5a3@redhat.com> <5d6b92d8-251f-463b-adde-724ea25b2d89@redhat.com> <996B013E-4143-4182-959F-356241BE609A@nvidia.com> <382839fc-ea63-421a-8397-72cb35dd8052@redhat.com> Content-Type: text/plain Content-Transfer-Encoding: quoted-printable 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XUK8QYkV4TvY56xZeAZmMBb1LhtxUPk5KPenvqbuZie9duFbPKHF4Bd2vqfkYxgTSTQXswthl+w0JSLM7tzj5cl3jlBn5E1uUUTgzjCLAPyvO29nmCizdhZ9Em5wOiQudrJD+Sf4t2f/KUiXgAmUeAYmtGpiE8jn0xukwhysneH3G2jIP3pDGpemYoYwCfw/ff05XTxmcUtGFedSldiQsckDoD+DTll3VmOtQ12W1fzHjhrOGhSBj+GtzClPu/JfxGwVVlyvZpEbmrDguLvJrokqpwPVpzo4WkfZf/S/HrIuhwJzWuV+bLr7Jq8RCgSsUh64EC8LQXVF2LHpEaHWnaod7fZjgzlP9UHwOcbhJ9eb4GY5p0VRmh88Fw1xn1+vuNb1PWFeaxzP3mVCxGBUvR9+kJjs33oeS4nCPg5sOWl9pzpmWEpuMFIDYFg== 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 22 May 2025, at 13:21, David Hildenbrand wrote: > On 22.05.25 18:38, Zi Yan wrote: >> On 22 May 2025, at 12:26, David Hildenbrand wrote: >> >>> On 22.05.25 18:24, Zi Yan wrote: >>>> On 22 May 2025, at 12:11, David Hildenbrand wrote: >>>> >>>>> On 21.05.25 10:02, Bharata B Rao wrote: >>>>>> Currently the folios identified as misplaced by the NUMA >>>>>> balancing sub-system are migrated one by one from the NUMA >>>>>> hint fault handler as and when they are identified as >>>>>> misplaced. >>>>>> >>>>>> Instead of such singe folio migrations, batch them and >>>>>> migrate them at once. >>>>>> >>>>>> Identified misplaced folios are isolated and stored in >>>>>> a per-task list. A new task_work is queued from task tick >>>>>> handler to migrate them in batches. Migration is done >>>>>> periodically or if pending number of isolated foios exceeds >>>>>> a threshold. >>>>> >>>>> That means that these pages are effectively unmovable for other pur= poses (CMA, compaction, long-term pinning, whatever) until that list was = drained. >>>>> >>>>> Bad. >>>> >>>> Probably we can mark these pages and when others want to migrate the= page, >>>> get_new_page() just looks at the page's target node and get a new pa= ge from >>>> the target node. >>> >>> How do you envision that working when CMA needs to migrate this exact= page to a different location? >>> >>> It cannot isolate it for migration because ... it's already isolated = =2E.. so it will give up. >>> >>> Marking might not be easy I assume ... >> >> I guess you mean we do not have any extra bit to indicate this page is= isolated, >> but it can be migrated. My point is that if this page is going to be m= igrated >> due to other reasons, like CMA, compaction, why not migrate it to the = target >> node instead of moving it around within the same node. > > I think we'd have to identify that > > a) This page is isolate for migration (could be isolated for other > reasons) > > b) The one responsible for the isolation is numa code (could be someone= > else) > > c) We're allowed to grab that page from that list (IOW sync against > others, and especially also against), to essentially "steal" the > isolated page. Right. c) sounds like adding more contention to the candidate list. I wonder if we can just mark the page as migration candidate (using a page flag or something else), then migrate it whenever CMA, compaction, long-term pinning and more look at the page. In addition, periodically, the migration task would do a PFN scanning and migrate any migration candidate. I remember Willy did some experiments showing that PFN scanning is very fast. -- Best Regards, Yan, Zi