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and promotion To: Bharata B Rao , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Jonathan.Cameron@huawei.com, 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, ziy@nvidia.com, dave@stgolabs.net, nifan.cxl@gmail.com, xuezhengchu@huawei.com, yiannis@zptcorp.com, akpm@linux-foundation.org, david@redhat.com, byungchul@sk.com, kinseyho@google.com, joshua.hahnjy@gmail.com, yuanchu@google.com References: <20250814134826.154003-1-bharata@amd.com> Content-Language: en-US From: Balbir Singh In-Reply-To: <20250814134826.154003-1-bharata@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR03CA0008.namprd03.prod.outlook.com (2603:10b6:a03:33a::13) To PH8PR12MB7277.namprd12.prod.outlook.com (2603:10b6:510:223::13) 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 2rxHWOcv 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 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 8/14/25 23:48, Bharata B Rao wrote: > Hi, > > This patchset is about adding a dedicated sub-system for maintaining > hot pages information from the lower tiers and promoting the hot pages > to the top tiers. It exposes an API that other sub-systems which detect > accesses, can use to report the accesses for further processing. Further > processing includes system-wide accumulation of memory access info at > PFN granularity, classification the PFNs as hot and promotion of hot > pages using per-node kernel threads. This is a continuation of the > earlier kpromoted work [1] that I posted a while back. > > Kernel thread based async batch migration [2] was an off-shoot of > this effort that attempted to batch the migrations from NUMA > balancing by creating a separate kernel thread for migration. > Per-page hotness information was stored as part of extended page > flags. The kernel thread then scanned the entire PFN space to pick > the PFNs that are classified as hot. > > The observed challenges from the previous approaches were these: > > 1. Too many PFNs need to be scanned to identify the hot PFNs in > approach [2]. > 2. Hot page records stored in hash lists become unwieldy for > extracting the required hot pages in approach [1]. > 3. Dynamic allocation vs static availability of space to store > per-page hotness information. > > This series tries to address challenges 1 and 2 by maintaining > the hot page records in hash lists for quick lookup and maintaining > a separate per-target-node max heap for storing ready-to-migrate > hot page records. The records in heap are priority-ordered based > on "hotness" of the page. > Could you elaborate on when/how a page is considered hot? Is it based on how often a page has been scanned? > The API for reporting the page access remains unchanged from [1]. > When the page access gets recorded, the hotness data of the page > is updated and if it crosses a threshold, it gets tracked in the > heap as well. These heaps are per-target-node and corresponding > migrate threads will periodically extract the top records from > them and do batch migration. > I don't quite follow the heaps and tracking in the heap, could you please clarify > In the current series, two page temperature sources are included > as examples. > > 1. IBS based memory access profiler. > 2. PTE-A bit based access profiler for MGLRU. (from Kinsey Ho) > Thanks, Balbir