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b=VsXNAyVwCKVC8F3brKcjy2i0Q3Se1u9PLt8EMAuTPn4JyXMDXYdGOTYb4gOlC4QJW hQ82+4E1eNEI2N2AXhljGYLhVXrAWP4MvG1nSl2nE4ACjjh97QVWZX2yk8Ig9csXd9 rqxRGlPy2yLut+EaIj/onPLhEw2F499Lj1i2s+fFIBd2bV4Cb5KXAjAgKcfXVwaGvH WL2zTB1FcKCvo9uypuHEVsYMwRPotzrVeYUhmWcLfL2alnUa0FEZP0sT3Nq8pGoE1C j7FncxtWhdfFvH9In36DhAXVEBSq/Y7Z6/7qmqXgaC6rol3x4E6yo1GNPRMboAI4PP uVna5eMSOHB4Q== From: SJ Park To: Ravi Jonnalagadda Cc: SJ Park , KunWu Chan , Kunwu Chan , akinobu.mita@gmail.com, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, akpm@linux-foundation.org, corbet@lwn.net, bijan311@gmail.com, ajayjoshi@micron.com, honggyu.kim@sk.com, yunjeong.mun@sk.com Subject: Re: [RFC PATCH 0/6] mm/damon: hardware-sampled access reports Date: Fri, 21 Aug 2026 17:32:35 -0700 Message-ID: <20260822003237.88274-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: F24D418000D X-Stat-Signature: s1ymp379tq4iung9wf7jfh1uoqdxfikn X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1787358766-102545 X-HE-Meta: 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 hLh0BUFG Xg1bky15I7auTxkBP5LZeK1mA9j7/TWcndamwmv9pQjFOE4C8HtREZrcLSsEy2JBYNNaUx/D9H8IQm5xe2inS/nyy0Fkrix7qZ1HNZDlrXStYPYFzGJNTYvP64rJ5hYuESzmFpSfr0ydzPj53qD05eoh8cx7S8et87N3/x+XpJPudPKz6ukvmq8vXTiFvU3jBy+vVU06SosgWVEVBnAHQfLNF04mVGcOG0EHjEi7xT3r2B5BJpsE4yAxVUlMjMDpiMvAOpeNQzrz1NpeE2a/MZ1h2GyCUivgjJYIrDjJY6BAjNRhjWk6NNfj73gVBnLo//bej2gr51zFk/jAOy34s17akAQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 21 Aug 2026 09:32:02 -0700 Ravi Jonnalagadda wrote: > On Fri, Aug 21, 2026 at 2:55 AM KunWu Chan wrote: > > > > Hi Ravi, > > > > Thanks for the detailed reply. The fan-in diagnosis makes perfect sense. > > > > > Your series is based on the v1 substrate, and the way an event is > > > configured is the part that moves most. > > > > > > [...] > > > > Glad to hear v2 is on the way. The probe-based model is actually > > something I encountered while building the AUX backend. When multiple > > sources can feed the same region (e.g. PTE scanning + SPE/IBS), the > > question of how to combine their reports becomes interesting. > > > > For example, CXL tiering may care about physical-address locality, while > > per-process monitoring may need virtual-address attribution. How do you > > see probe weights being determined — is that expected to be > > scenario-specific, or is there a more general principle behind the > > weighting? > > Hello KunWu, > > SJ can answer that authoritatively -- the probe and weight interface > is his. Here is my understanding which SJ can confirm later: > > Weights are relative, and only among probes. A context can hold up to four; > each report carries its probe index and credits that probe's own hit count, > so two PMU-based probes in one context are scored in proportion to their > weights, and that is where a scenario-specific choice belongs. > > What does not mix is a weighted probe with the other two sources. Any > nonzero weight switches the whole context to probe-weighted scoring, which > turns page-table access checking off -- so SPE cannot be blended with PTE > scanning, it replaces it. Page-fault reports carry no probe index; they > credit the region's access rate but have no hit count, so under weighted > scoring they are not part of the score either. Both coexist with a probe > only at weight zero, where everything feeds the same access rate and is > indistinguishable afterwards. > > So for your case I would read it as: PA locality and VA attribution are > different targets and different address kinds, which points at separate > contexts rather than one context with tuned weights. Thank you for detailed response, Ravi. Ravi is correct. Physical address and virtual addresses wouldn't be able to be monitored with a single DAMON context. The user may need to have a DAMON context for physical address space, and another DAMON context for virtual address spaces. Thanks, SJ [...]