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Wed, 08 Oct 2025 10:59:39 -0700 (PDT) MIME-Version: 1.0 References: <20250910144653.212066-1-bharata@amd.com> <7e3e7327-9402-bb04-982e-0fb9419d1146@google.com> In-Reply-To: <7e3e7327-9402-bb04-982e-0fb9419d1146@google.com> From: Vinicius Petrucci Date: Wed, 8 Oct 2025 10:59:01 -0700 X-Gm-Features: AS18NWANBul6dbj_HkmY5fIi05_D6Oecvga0iBOa6pPxhI_sCfcpoYxSf9FgW9E Message-ID: Subject: Re: [RFC PATCH v2 0/8] mm: Hot page tracking and promotion infrastructure To: David Rientjes Cc: Gregory Price , Matthew Wilcox , Bharata B Rao , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Jonathan.Cameron@huawei.com, dave.hansen@intel.com, hannes@cmpxchg.org, mgorman@techsingularity.net, mingo@redhat.com, peterz@infradead.org, raghavendra.kt@amd.com, riel@surriel.com, sj@kernel.org, weixugc@google.com, 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, balbirs@nvidia.com, alok.rathore@samsung.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: y4nyz9sg1tpohtkme561qbk9qsdm756r X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0BE7918000E X-HE-Tag: 1759946381-815964 X-HE-Meta: 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 ACsFz2xp MWuwTS/UC23UcOEYV2RrhlZrQ7HFck1u2PpmA30g/5NPr5lvIGdD1gWGf9c9z4x96zvn2E32iDD919x7Bg7t+d4xdrsDXxWuWINGCcrNSG5be16kYgGKpeBuJplC2StNSwhq7gDQTZTrE/AQkYAPCKZnMjWG7z7yT7hZ4m0cjLLY/WSTL4nHQKuJEKe11eLPcXFtuTqeV9PihThiNDghqVk+5e+OoSwqneEi2C4YUZGZk2SakzTsjMdGl7sYH25ie1NiqlRK6vkzJjQ5WT590exgeqK9jPmdB39XnXB49Vrg6oxqMOsCNctR2c7AI6t0TT988UHch1l5CkA+6IV0cUImwmBzU2duGeYIUJ7E8ine+i4CproCYmyYUN8JQl3JZdQB/P1ohVI9amK7FaddrTmJf37YIw5WGXpGeDkVSBNVRB1mfGKcBIZFH+lkRFL1Hsvqvq5cz7Dcu7WtM28Qnqu+LQD/tME7M5F4S 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: Hi David, On Tue, Sep 16, 2025 at 1:28=E2=80=AFPM David Rientjes wrote: > > I've been pretty focused on the promotion story here rather than demotion > because of how responsive it needs to be. Harvesting the page table > accessed bits or waiting on a sliding window through NUMA Balancing (even > NUMAB=3D2) is not as responsive as needed for very fast promotion to top > tier memory, hence things like the CHMU (or PEBS or IBS etc). First, thanks for sharing your thoughts on the promotion responsiveness challenges, definitely a critical aspect for tiering strategies. We recently put together a preliminary report using our experimental HW that I believe could be relevant to the ongoing discussions: A Limits Study of Memory-side Tiering Telemetry: https://arxiv.org/abs/2508.09351 It's essentially an initial step toward quantifying the benefits of HMU on the memory side, aiming to compare promotion quality (e.g., hotness coverage and accuracy) across HMU, PEBS-based promotion, and NUMA balancing (promotion path). Hopefully, this kind of work can help us better understand some of the trade-offs being discussed, support more data-driven comparisons, and spark more fruitful discussions... Best, Vinicius