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Mon, 2 Mar 2026 12:15:36 +0000 Date: Mon, 2 Mar 2026 12:15:35 +0000 From: Jonathan Cameron To: David Rientjes CC: Davidlohr Bueso , Fan Ni , Gregory Price , Joshua Hahn , Raghavendra K T , "Rao, Bharata Bhasker" , SeongJae Park , Wei Xu , Xuezheng Chu , "Yiannis Nikolakopoulos" , Zi Yan , Subject: Re: [Linux Memory Hotness and Promotion] Notes from February 26, 2026 Message-ID: <20260302121535.000001ed@huawei.com> In-Reply-To: <855370d6-811e-5864-b93f-c5bf4b6e27b3@google.com> References: <855370d6-811e-5864-b93f-c5bf4b6e27b3@google.com> X-Mailer: Claws Mail 4.3.0 (GTK 3.24.42; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.203.177.15] X-ClientProxiedBy: lhrpeml100009.china.huawei.com (7.191.174.83) To dubpeml500005.china.huawei.com (7.214.145.207) X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: EB9C380010 X-Stat-Signature: yzj7kehukfkafy5j4sp99g9ob8z6ehcn X-Rspam-User: X-HE-Tag: 1772453741-87108 X-HE-Meta: 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 NeLE7ENl 94JAeCzeR5EIcrdfwIzgSp0jO6xs7a6vs5CthmTRQK14fMr/Ksjg6YYSGOF5Ajus/3YMCapSTtrUIHpqdjkqAHMU+7O5I5ihhEdLQdi0Pm/Xf6fdVmP5lQcBsMNSh4FTGNty333HB5b4E85t6fn7A02F8NUGDnC6DBdedn5bwOw1k/EwRhLtgLjPbmWjhHtLg/BIHczPCWV287+gOyBK9YOje2C0zMutKJhDILvDjpTYmpti4fN0H9blTuxI1aLDyd3Fr7T3CnQxm6yAxMmhTAWs+npV6CRaIEFEhvt/pC48rj+g= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > ----->o----- > We touched on the CXL Hotness Monitoring Unit (CHMU) and whether any work > was on-going to abstract this in upstream Linux. Both Google and Meta > were not actively looking at this. Yiannis suggested Jonathan Cameron may > be looking at this for qemu and testing. We concluded that not having > CHMU support upstream is not currently holding anything back and it might > be addressed in a year or so; it might also be solving a problem that > nobody has yet. On this, sorry I didn't make the call. Whilst we have some minimal support in QEMU for emulating the CHMU to allow data capture, and a tracing style kernel driver my priorities currently lie elsewhere. I might get back to this a little later in the year. I'm aware that some others have been experimenting further though but heard how they are getting on yet. > ----->o----- > Yiannis brought up non-temporal stores for tiering and the possibility of > finding time to work on it in the next few weeks. He saw great value in > this from the compression side and was trying to determine if this brings > value to CXL or tiered systems in general. The idea is to extend > migrate_pages() for the demotion path so it uses non-temporal stores -- we > don't want to warm up our cache for cold memory. Gregory noted that we > want to ensure that when allocating the folio as the migration target that > we would also need to make sure that's not in the cache for this cold > memory. I noted that Shivank from AMD had previously presented to this > group about enlightening migrate_pages() for hardware assists and using > the "reason" field of migrate_pages() to differentiate different use > cases. I'm also keen to see progress in this area. There are lots of options for bulk movement of data and tiering brings a specific set of constraints / opportunities that perhaps don't apply so much elsewhere. Jonathan