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bh=kIt0MX12ycDk124SAeYfFyNpLYyys/OHkSbkyqFSd78=; b=r14Ntvlw7N4hXXouU2tMgWyzzThXfr9+u4snLhJx1SQEAk/yES+nQQDuAqeXbh1y3238eQ eEubB2qxNT+0ZrqFKphtpgzAx9AKlIFQ3gyT8LWXdwRa8mttDADHfUcnUxhBM112awF1Wm djDqZFs3FdWwLs0eQfsrp11aRpreImI= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=mfsMOuqV; spf=pass (imf22.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 11D694189C; Mon, 29 Jun 2026 18:33:37 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE0D61F000E9; Mon, 29 Jun 2026 18:33:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782758017; bh=kIt0MX12ycDk124SAeYfFyNpLYyys/OHkSbkyqFSd78=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=mfsMOuqVYVS9UEV1G+8hUcr0Tigrrwz1wkeQMOTs6i6G5h2N5jU+93Zs7uQJ1KRU1 0fL9nbfq3qm0fpsIYs1Fv949GutXWWyFhS5GZbu4n1/2OYfcYGv62dkSd52Y7wfQ4t CIvt/YvXmWyaNWCeuZBiYDAB4zDWbTS6q2sgX/Abi6n9teX+qMPUNvkmNCfQIKlSJw ITM9tJbMI5xUhV0XW/PTfW534cF04h5795BPrnzjsSK6EqagfYMikk+OtObnpQcDYL cEPhKemQ2PH9y1vo9u/pwW7VQFyapb4ZoEarPk8I3hf05cC2sGJEVUGPd2wRB0zw7k gYw4j9d8JykPA== Message-ID: Date: Mon, 29 Jun 2026 20:33:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: mempolicy: fix automatic numa balancing for shmem To: Johannes Weiner , Andrew Morton Cc: Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Neha Gholkar References: <20260629163337.1264881-1-hannes@cmpxchg.org> 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: <20260629163337.1264881-1-hannes@cmpxchg.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 3phc8txm6jigtmrysztw7wkdx7e8xy39 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: F3F5DC0002 X-HE-Tag: 1782758017-932741 X-HE-Meta: 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 HAmAgTPU wtyLiESEcp555IAQ6MvLSyQ1ThI7PejLSj1hwf4j4YVbf43+Rm++3cc4cLdYSTyun8C22Gtwhd/wcB0HGDRJv0JblX4IrSu6DNwlQ7ynNOYld1J0/7ZUsdUwTdhKuodOMJ3yA1yuBms3V7qUSehxAXxMruNg8ddMTkOYzjVMNtp0S1qgCVC1u5nslA01XhPZBpsUa08VWP0uGfPyAK0HTJve0dec/71lPgfQ7jOBKMJFgEI4vttL+K/EviB4wjERovCinLi6qoY9LJQqRYEIL6NmH1MiJXUKgDUDonXIY/jDwz9VdqhFSmEmbtJP7bT2r6HGN8dZCWjhC6G/RwDVIhlMi46Mkjw0N3PcHPNvbEpjF/KnP3STmvVMbmNFzzKOkdFotaabdSIUC4sBDij+I++tLYzsqD2PCQY9ii3mn2tgtHKSxDA922f9YY9byU8aV7Aj0 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/29/26 18:33, Johannes Weiner wrote: > Neha reports that mapped shmem aren't considered for NUMA balancing, > noting convergence problems and bandwidth bottlenecking for cachelib > based workloads on tiered memory systems. > > Looking at the code and going through the git history, this doesn't > actually seem intentional: > > Commit fc3147245d19 ("mm: numa: Limit NUMA scanning to migrate-on-fault > VMAs") added a vma_policy_mof() gate to task_numa_work() so VMAs whose > policy lacks MPOL_F_MOF are skipped from NUMA balancing scans. The > motivation was a real usecase: Oracle was pinning shared segments with > mbind(MPOL_BIND) so trapping faults was both expensive and pointless. > > The handling of NULL from vm_ops->get_policy, however, treated "user > explicitly opted out" the same as "user never specified anything." For > VMAs whose shared policy is absent - the common case for shmem - the > scan was disabled too. > > This issue is old. It probably hurts less in conventional NUMA. But it's > very noticable on tiered systems, where entire tmpfs workingsets can get > stuck on lower-bandwidth memory. Sounds bad enough to warrant CC: stable? > > Fix this by having vma_policy_mof() use __get_vma_policy() directly, and > thereby handle the fallback to task policy (-> preferred_node_policy() > has MPOL_F_MOF per default). Every other consumer of vm_ops->get_policy > already handles it this way, the scan-eligibility check was the outlier. > > This preserves Mel's intended fix: don't scan stuff the user explicitly > pinned. But allow default policy vmas to participate in balancing. > > Reported-by: Neha Gholkar > Tested-by: Neha Gholkar > Fixes: fc3147245d19 ("mm: numa: Limit NUMA scanning to migrate-on-fault VMAs") > Signed-off-by: Johannes Weiner > --- > mm/mempolicy.c | 21 ++++++--------------- > 1 file changed, 6 insertions(+), 15 deletions(-) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 36699fabd3c2..bba65898aee1 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -2057,24 +2057,15 @@ struct mempolicy *get_vma_policy(struct vm_area_struct *vma, > bool vma_policy_mof(struct vm_area_struct *vma) > { > struct mempolicy *pol; > + pgoff_t ilx; > + bool mof; > > - if (vma->vm_ops && vma->vm_ops->get_policy) { > - bool ret = false; > - pgoff_t ilx; /* ignored here */ > - > - pol = vma->vm_ops->get_policy(vma, vma->vm_start, &ilx); > - if (pol && (pol->flags & MPOL_F_MOF)) > - ret = true; > - mpol_cond_put(pol); > - > - return ret; > - } Okay, we used the fallback of vma->vm_policy before (if vma->vm_ops->get_policy was not available), which is what __get_vma_policy() does at well. But if vma->vm_ops->get_policy now returns NULL, we fallback to get_task_policy(). Makes sense to me although this is a source of confusion for me. Acked-by: David Hildenbrand (Arm) -- Cheers, David