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Fri, 23 Oct 2026 20:14:55 -0700 (PDT) Received: from [2a00:79e0:2eb4:9:aa88:ce75:c103:41a4] ([2a00:79e0:2eb4:9:aa88:ce75:c103:41a4]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cd8cccce585sm155624a12.26.2026.10.23.20.14.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Oct 2026 20:14:54 -0700 (PDT) Date: Fri, 23 Oct 2026 20:14:53 -0700 (PDT) From: David Rientjes To: Davidlohr Bueso , Fan Ni , Frank van der Linden , Gregory Price , Jonathan Cameron , Joshua Hahn , Raghavendra K T , "Rao, Bharata Bhasker" , SeongJae Park , Wei Xu , Xuezheng Chu , Yiannis Nikolakopoulos , Zi Yan cc: linux-mm@kvack.org Subject: [Linux Memory Hotness and Promotion] Notes from October 22, 2026 Message-ID: X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: B27CD140006 X-Stat-Signature: 5pt6i6pxdtxuyw1ckrs5fpi43nzpfpwo X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1792811697-328791 X-HE-Meta: U2FsdGVkX1+P5D27J7AcyMHNJHFV6275h14FY1UIOYQTWVrxJpA+6BgWbDbwxrNL78JoTsu0CUgopQFYre4Qqx9CVbYmXXk6wrtZEF6+30Gv7cC38FsJ0ie5BCfi3pi1Dnnou7HtcXBcPvXzhDzPHFxjyil6HTfLi0W6vccfFtRdU4yS6IMRNNpnbBFBGO3XlBTaTzWrWed35S8oPESATbwx0y3rTNZDY+cLO7+0/SB9ZZsCM7XDUv5hygWuOuSUuWm1HeTM9s/ym11U1W7pI7L3QobdCEMOjLypvqPdR2OpI5ljG+W7vpoGaYtkpmHelmHeaL1HngiWGgEovGOyRFtx86XHNfVjL1xv6UsFdQxlfwfabuIuQQ6uQgnphhUo6MZ5jd3s0auT7sQ1yfCsI/gZQUzjvJivYmgOi6/68Ug1juhR9jawBQdZ7bN/8EGihEFgkQBsAWFfpY4+NinX/iKq8QkDU2Ht7ujvHd03uoAM3SuxVsoJnv9aBTMSh7LqCoDQN3hf9KujwXa8HXS6hTlv++WvQkViJz/RhpcB8xPOzwHO0fwoHV3z+LDloGnlJDsx3JAguVD1PaciWA+RzuO++wxk2UTXlJn3IBkiUKa2ScH62onBQA6gsjecxJ5Q5K6e3yDrmq0JaMHKZQr1UyNASxHvsyHHTEwr4PB22iQA0Fhv5w4jye7lvD/gL5VVAPHpHoCsJdJ2fpkR5gMdAQzpggJv/4/7X3GXNTaPXlzFqYX7NWM8ZWTj2aDXa6lTmAY48tQMstEJvaYolWBedXF3PUi9ZyB5ZEoIVhKrV0xYg0uajS5XAf0I1nBmsx2/tIT6125eMN2+Md1xw2aKC+l1U2R+HaNU5FQq1ixH8eZRiMW3YWqZIJUUNznZwjRVTUtV0Mkl3/KRusRD9zqNbx57aoASniAqo1/w2FxFlBiU5klVWJLHjhUBu0VbhD+wp6mmeBsNCpPqkmSrV/3 005/ln9Z A/E13ltR8HOPOele9pTa8ptamUOzsgnAPEnM+3zmTnPnwq+23Fzt2pdFZ9rGAuGD3cSnHVXRMM2UYaHNDp9anmXjOrCQomcsM8jYkP+7pmHJESlhTtm9ORrR1lZRGgr8WbS1/Kufm85BQ2c7GtT4bJ4jG9K+JVuxYSF9WHb4mzonDoH9d09sKfBSy7h68I2WPN7F/9HkAqqvTgZ2gYjtOzJKgBlKR5u6trRX8hWy/awMq0UoSx79C2Xd8qmqFkimAYPPRIavj00ICeAzgVeb5xlQbUd+9ZQ2f4B3UGh8r9Q/sVnU8DD8EvgKWdiOUPKqAIzvGXEG2hWmxg0vez06pOMOroU2Wn47IesJqUZgBBAczvpmsmelwq0/6NK1PYBS5E63Vr79m8i0mZqWT+xH35OcNcOUwnujQIiVJcYCsXl8KKTYNmTTpjYkyIQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Hi everybody, Here are the notes from the last Linux Memory Hotness and Promotion call that happened on Thursday, October 22. Thanks to everybody who was involved! These notes are intended to bring people up to speed who could not attend the call as well as keep the conversation going in between meetings. ----->o----- We debriefed the relevant discussions at LPC to bring everybody up to speed. Bharata said the clearest outcome for him was to separate out the asynchronous promotion mechanism and establish its independent value. After that, sources of page hotness and hardware specific mechanisms could be integrated into the kernel. Wei suggested getting the asynchronous promotion mechanism merged soon so that other things can build off of it. Bharata said he will try to post the next revision before the next meeting. Gregory noted that there may be some pushback on asynchronous promotion with regards to cgroup charging of the cycles. Davidlohr noted that this matched his expectation and that he is working on upstreaming the CHMU support as a CXL driver, currently using DAMON as its backend. He'll then wait to see the outcome of the other patch series in parallel. Jonathan questioned how integration with DAMON would be done to eventually support the asynchronous promotion stuff. Davidlohr said this would be done in the most generic way as possible. CHMU has a natural interface with ranges and large continguous chunks of memory that can be passed to any interface. If pghot is confined to the NUMA Balancing aspects, then CHMU wouldn't be integrated with it. Jonathan asked if we're really getting large contiguous chunks of memory from the CHMU and Davidlohr said this is what he is seeing in his evaluation. Bharata suggested it may be difficult to get the configuration of DAMON correct, this is a complex undertaking. If the only way to use CHMU is through DAMON, this may be challenging. Davidlohr agreed the configuration was more complex but if you're going to go out and buy a CHMU supported device then you can likely configure this correctly. Wei asked if the CHMU is implemented as a driver and Davidlohr confirmed that it was; in this case, any backend could likely use it. Davidlohr said he would send out the CHMU series and then extend it through sysfs before adding the missing pieces in DAMON. Gregory made an interface that took a list of physical addresses or folios, the idea being that a driver or external service would send CRAM information on the memory to promote. There didn't end up being an important reason to only be in CRAM, we could implement support for private nodes. For normal memory tiers that happen to be on private nodes, the hotness becomes important and can require additional plumbing that will evolve over time. This will become more obvious as private nodes moves out of RFC and into a formal proposal. Gregory updated on the CRAM discussions as LPC. He had a lot of discussions and there was general openness to the first user being HBM as the minimal upstreamable place. There isn't a big leap between this and CRAM. Jonathan asked how hotness tracking is being done for CRAM today, and Gregory said it can technically support NUMA Balancing and another approach is pushed off to the driver by telling it what to promote. He'll post the next revision of private nodes after the merge window followed by CRAM. ----->o----- Huan updated that he had sent patches to Yiannis for supporting non-temporal stores and memory error handling. He will post these to the upstream mailing list soon. It supports folios, not just 4KB sizes. There are some changes to the interfaces that are in flight that may result in some changes. ----->o----- Shivank discussed two concerns for page migration hardware offload: (1) there's an assumption that SDXI would be idle so there's a concern about other processes using it -- there may be competition between kernel and user, (2) if batching folios for migration, there may be latency before the first folio is available. For this, we could use a migration mode that is not sensitive to latency. He is planning on getting the easier bits merged first. ----->o----- Joshua noted that he was going to follow up on his tier aware patches after the merge window and requested that anybody with use cases for it would express that on the upstream mailing list. ----->o----- NOTE!!! The next meeting will be after Daylight Savings Time ends, so the meeting will be one hour later if your time zone does not make the switch. Next meeting will be on Thursday, November 5 at 8:30am PST (UTC-8), everybody is welcome: https://meet.google.com/jak-ytdx-hnm Topics for the next meeting: - update on Bharata's asynchronous promotion mechanism separated out from the rest of pghot, targeting posting the revision before the next meeting - discuss current status of CHMU driver and its integration with DAMON or any other generic backend as needed - update on private node support as well as CRAM to be posted after the merge window closes - update on combined patch series for supporting non-temporal stores in migrate_pages() with memory error handling (series from Yiannis + Huan) - discuss Shivank's series for enlightening migrate_pages() for hardware assists and competition between the kernel and user use cases - update on Bharata's support for sources of page hotness and hardware support - Teja's update on SDXI page migration based on AMD patches and hardware issues being encountered that do not result in page migration - update on tier-aware memcg limits status and production testing based on the latest major overhaul - first class support for virtualization based memory tier support, how to leverge memory tiers in the guest Please let me know if you'd like to propose additional topics for discussion, thank you!