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b=Yb3i7jEn4N15nyx7Kxt0QjPtrqbkEwaoV8ivyObe1Gmy7WOcD5YND9weJBaOfNiOj Kcev7VDm2ubmChGfN1Y4IagPj1iUXxKU9OnC27cs+zZmy/HcSKj9w/ELMvDNQIDiv6 N+BZzUMa1RfhieTctY0KISwmTtzkYkuEVmTQrv2G6kyPsZhQVZSqiESa9p6bqtXpXF fQ0wYtOGGxRpEoSoyeM+klEvp6C3/dkobi826qkB3pBeCHE9vVYeZxoUJdD1di3xfs FfNJFfLp81uOtKkfDt/FzAYY6J6xM+mCAPJ01hSFoSUQwvx1fmiVNLZaU+quPu+imV YUkkEoCPpf4Ew== Message-ID: <13a3b600-8a87-478e-adcc-2425c75f98c6@kernel.org> Date: Tue, 27 Oct 2026 14:04:49 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/mempolicy: recompute automatic interleave weights on memory hotplug To: Gregory Price Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, ziy@nvidia.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, honggyu.kim@sk.com, stable@vger.kernel.org References: <20261024170415.4121901-1-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-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: D47CA18000C X-Spam-Status: No, score=-7.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Stat-Signature: qybo1m6qy5bpad138aeq9ztis8zb148f X-HE-Tag: 1793106295-308859 X-HE-Meta: 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 NxLR7vig 8fSTxq9G4/etx1LWb3RjYS4M7I6oEXUJE4u9SGoXbWOnQHM/d5fAza4Zj+xL9Uspxa1jW5ziFeN3z2hDOxOiWf3YjALlqGiXeMcqkBjuwBmoaFl7YV4WZBXVXAK8XkEyBBO01mEt80k04Uvx9JtzBuZMkeeMMNCj3Xdm/g8PhgAMQIafm9Zms4J8/bWuzxACundz+zV9yg6+yoaGcentEi9PrFSJBAm7U6gN6yYAlI0vs135P3jguJrUyqKJUeDxO6xnryEZeZK/hvmAfSf4e+1wOYZr1mqRAPhxK5n0MyX9w8FH2UMh1I5jcqQ8ZYxw1cdDulVRhhkDiTRw= 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 10/26/26 16:47, Gregory Price wrote: > On Mon, Oct 26, 2026 at 12:19:21PM +0100, David Hildenbrand (Arm) wrote: >>> +/* Recompute the weights from node_bw_table, unless they were set manually */ >>> +static int wi_state_refresh(void) >>> +{ >>> + struct weighted_interleave_state *new_wi_state, *old_wi_state; >>> + int i; >>> + >>> + new_wi_state = kmalloc_flex(*new_wi_state, iw_table, nr_node_ids); >>> + if (!new_wi_state) >>> + return -ENOMEM; >>> + new_wi_state->mode_auto = true; >>> + for (i = 0; i < nr_node_ids; i++) >>> + new_wi_state->iw_table[i] = 1; >>> + >>> + mutex_lock(&wi_state_lock); >>> + old_wi_state = rcu_dereference_protected(wi_state, >>> + lockdep_is_held(&wi_state_lock)); >>> + /* NULL wi_state assumes auto=true */ >>> + if (!node_bw_table || (old_wi_state && !old_wi_state->mode_auto)) { >> >> >> I was confused about the node_bw_table check at first. Maybe >> >> /* >> * We can get hotplug events before any BW data was recorded. >> * ... >> */ >> > > I went back and forth on whether to do the mutex in or outside this > function, but ultimately decided inside is just better structurally. > > But yes, this comment seems warranted in this case. > >>> + /* >>> + * HMAT and CXL report a node's bandwidth only when it first gains >>> + * memory, so recompute the weights whenever N_MEMORY changes. >>> + */ >>> + wi_state_refresh(); >> >> If the function fails, should we at least pr_warn_once() ? >> > > The only failure state is -ENOMEM, wasn't sure that was worth warning > on. I actually debated whether to just make this a void function. > > I don't have a strong feeling here, but happy to add a warn if you > prefer it. I'd assume we'd at least want to tell the world somehow that something is now imprecise? Or is not updating that harmless? -- Cheers, David