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t=1792482959; bh=mG3kNywBpCjlsN90sZBCwLqBblspQOk2h7zQBNKp7wI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=DvxGAV+OaraT9ljQafttLtkjrCxCFCziGjRjdD6HwDSpmr4+0+MkXiqlz3dN3LkvR MfM/McOKEjS6LdRZ6VGYT8CWPrJhfnxWW1JkPviBcxyJrcCOm6OYTyoDRKnLxDzXlJ gygE0Udc9/JKsQXMuoyTGMOiyu0lM2/HJ4EK04aOfsQ60EhPsIji7jnMWfon937KHA Ry9q64jMwMhte7oWL6nK2TbfURYsSEwUAOTeWoV8lik4nsuFWIv4b7hJNTI2x4/F8O 7YwJlW32gApnjMaxcZR64YRoxdu+mtO7KqcMSGUdLoFSnKOIkdJY0ZbdF6xyEHG1gX XXeczGddFlPoQ== Message-ID: <70771a19-9392-4fbb-8aaf-dcd40f60e977@kernel.org> Date: Tue, 20 Oct 2026 09:55:54 +0200 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/memory-tiers: reset demotion targets of nodes without memory To: Gregory Price , Zi Yan Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, weixugc@google.com, aneesh.kumar@linux.ibm.com References: <20261019184712.3422641-1-gourry@gourry.net> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: jaeej13oq1h5ipwcyi965akj6xo9ig5c X-Spam-Status: No, score=-17.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 039C620005 X-Rspam-User: X-HE-Tag: 1792482959-567075 X-HE-Meta: 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 UlHHeTfn JH3qUKOR7D7uGXzMWxSzQULaGdAgpIDjvMY3KYNN0Y28/3aSwSTDN/M9xedrX2owGveBb3tfI65kGw46/0YlVodD9PCErcFlKxPowDxEJ1pO6sdSSwNzgwL2XEF5OtIHHe0NgNGuV73stv0PGYQox8vQEouP+vSpM6M2IETFRZEt9uc2akP/44+b9YAQ2gsw6D7op2/gZw+uyDKRlQOY3FzNoXksSVJ85/eghmJWMia79MpcVoRF/TZQHJDbYhrX22UE4dEfcJ4FEeFSFzp6oC/vYSS9smqaVz9ICm8sPkUR4h5uEP4Z6s73Xgt+yEfEnjPst/k+xcrIK38iIrIjfsC9Bla6vgy9riNK7l40LvQpOOyEgg0iJFyJRJEt1y4Sm6jIZ/GvbJLXw82o= 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 On 10/19/26 22:22, Gregory Price wrote: > On Mon, Oct 19, 2026 at 03:04:45PM -0400, Zi Yan wrote: >> On Mon Oct 19, 2026 at 2:47 PM EDT, Gregory Price (Meta) wrote: >>> When a node loses its last memory, offline_pages() clears N_MEMORY >>> before the memory-tier callback rebuilds the demotion targets. >>> disable_all_demotion_targets() resets only N_MEMORY nodes, so the node >>> keeps its old node_demotion[] entry while it has no memory. Before >>> 6c542ab75714, the reset covered every online node. >> >> establish_demotion_targets() uses for_each_node_state(node, N_MEMORY), >> because the to-be-online node is already added into N_MEMORY? >> > > NODE_ADDED_FIRST_MEMORY happens after the memory is already added > (though not necessarily online). > > NODE_REMOVED_LAST_MEMORY happens after the last memory block is removed > (and therefore N_MEMORY is gone). > > slightly different timing for each event. There isn't a reasonable > change we can make otherwise. > >>> >>> A reclaimer reads the stale entry only between the node regaining memory >>> and its targets being rebuilt, and it filters the entry against the >>> current allowed targets, so there is no user-visible effect. To see it, >>> online and then offline a node's only DIMM: a debugger still finds the >>> lower-tier node in node_demotion[nid].preferred. >>> >>> Reset the targets of every node. >>> >>> Fixes: 6c542ab75714 ("mm/demotion: build demotion targets based on explicit memory tiers") >>> Signed-off-by: Gregory Price (Meta) >>> --- >>> mm/memory-tiers.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c >>> index 25e121851b586..7197f1a67a340 100644 >>> --- a/mm/memory-tiers.c >>> +++ b/mm/memory-tiers.c >>> @@ -378,7 +378,7 @@ static void disable_all_demotion_targets(void) >>> struct memory_tier *memtier; >>> int node; >>> >>> - for_each_node_state(node, N_MEMORY) { >>> + for_each_node(node) { >> >> I think the above code deserves a comment explaining why for_each_node() >> is needed instead of for_each_node_state(N_MEMORY), because when a node >> is added or removed during memory hotadd or hotremove matters here. >> > > Sure. Will respin tomorrow and give others a chance to look at it. A comment makes sense to me as well, it's not completely obvious. Apart from that LGTM. -- Cheers, David