From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793106295; b=GQzN6q2kbNZ2Wxxxds+JKfFnyJdmrhhwdtHgT/gETxd0AjUuAMae0iSBFfVnqCfu8g8m UPV+Eo0iQwub586u2HPXukxYFR5Ps1MA0Ty9BuqDoG4HOw4Cfsy4zeK4nsyswSIOKDV5h 1Q4VY4EPBX7j6U+6b2ckLyftcCoWp72Nr424PmnwcY34QXF6pnlfLtTOGIBPlSw1KDiLP aDIAlxwxw4Qu9pBHmlSjFVIEOy3dhvQErEUE1E2mudYFlP4cODld1aNgSHKU5cobSF1XU 4bxTS87pmSte81mAo1gjXpexwhiy3Lb9CX/3F8FB3qDBbX2srwkPLSZFnMLzKSI9ANg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793106295; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=Of4H9m4bb+oakg+uaiUFhL/+GkDlyL+JKLZHKgUUKW0=; b=TPZBjpqnUgT/TGpB4ZLETZHuupfi6seioD5XIDuYh92i6UHZUv28uRhZEX9dYWXbiMuS 1vWtEE9UqZI0iOuZQxsXuKKX/JDv4ASBTfTmboiRRF8zNQE79PgRQSxvbMkM3c75TX3IJ kzCvV64W6XgLgYH9ZzxhYRBLD9/O2rCqTsY20Zng0LIgqS8qviOjC26ANqCvNY7dMTTIv Wgo+U6Zu3K7By4oZbG21XTntA0F8UVB1Q7sP41WzrFlxk0LAu7JNPC59ysmJoD7od0CLr TZ9VFYgrr/8UWfz5iicAXKmmUk9e7cYvIbaVRaa8trxBy+pNBaKTGgBsTUMZRTYnaiQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Yb3i7jEn; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 344D7606A31B; Tue, 27 Oct 2026 13:04:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Yb3i7jEn Received: by smtp.kernel.org (Postfix) with ESMTPSA id 55CBC1F031E6; Tue, 27 Oct 2026 13:04:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793106295; bh=Of4H9m4bb+oakg+uaiUFhL/+GkDlyL+JKLZHKgUUKW0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; 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-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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