From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BBDC41E8320; Tue, 16 Jun 2026 12:19:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781612348; cv=none; b=l+ik6jo45d2U1nOVKtrWmCE1ci1UOCq+iK4MsMS6NOcZ7KygXCoZANIK+8tfEl9w+kGmu46gOnP9nRARQ1e43mP1ifc+/M7/NwKuEPRdr0qarIPRSfactKnkMlR5N1VGEEdAuVcQFaDMFNZT2j5yAFux2GaA638FXzmXCLFnSHA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781612348; c=relaxed/simple; bh=n7J534/YF+z0xcV0zPOykFP58b0UqYCnbq5cW0NDDcc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=FqWx6Bi7kra0VL4Mh5TSrtQyH2WLFj7IpOzQhZmYNiOwuriuWYGRThtHtji8X+U4/8EItcJtUCKxjPGy9EGaq8fZ7WYGhfVcWNYya6PdglkmSh6I1qCQp9WCtatTuJyaMBy/BJu9oHPiXvhwtZPK6hbG6dNr0gVYp+P855e6ztE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=G7PAozou; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="G7PAozou" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4B7D81F000E9; Tue, 16 Jun 2026 12:18:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781612347; bh=c/G2myNx4fiCaxX6PsWVQpl+0Cqyxt28MVOGrtWV4gE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=G7PAozouuUOOEBEgkwucE0pBmvJOplyCv6dNF7ZqldkXevK+Bg+s5Gl9IJcW0LUs6 dm6CZcVDEuzKzIYQ2zG+9CVvBqLY9+SkgoKCUvUWf++U6pujWfn7eDN6AdJFDo1LOp bUm7CeOR/v30xvmVfY5QMhoLBjM7+hCZcJVvgtuXeLxQDM45SMA6xF9vc5P0HXg8E5 nXm7dkXvTURT+aoxVC5jNW5XLDj9A17dJOKS93f9AVBWeNq2wRDxm9LUquOz+5YftM gtpULl+i0virYMwv2sXdj62adUPgZlfu+MWhlyxkxDSawqVyFaYyufY1RCDbDrqh93 vl2uWgFOCHYfw== Message-ID: Date: Tue, 16 Jun 2026 14:18:57 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH splitout] mm: memory-failure: serialize TestSetPageHWPoison with zone->lock To: Miaohe Lin , "Michael S. Tsirkin" Cc: Zi Yan , Andrew Morton , linux-kernel@vger.kernel.org, Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Muchun Song , Oscar Salvador , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Hugh Dickins , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , virtualization@lists.linux.dev, linux-mm@kvack.org, Andrea Arcangeli , Naoya Horiguchi References: <20260609111020.e88f51a7b6ebc37360d66fdc@linux-foundation.org> <8c1f468e-b50a-487a-a267-8d1ea5a61c87@kernel.org> <38C84F23-E881-4DB2-86BA-93F39D44AE1B@nvidia.com> <20260609162437-mutt-send-email-mst@kernel.org> <4BA276D9-9EB9-4E2A-8A05-657ACACFF227@nvidia.com> <20260609165829-mutt-send-email-mst@kernel.org> <20260610171646-mutt-send-email-mst@kernel.org> <14537566-94d9-eac5-2636-35f925a9d159@huawei.com> <20260611013644-mutt-send-email-mst@kernel.org> <1b5676ab-0dc5-ef33-9d79-a2bd6090a62d@huawei.com> <984d9775-e17c-0231-b021-126b13a9aa42@huawei.com> <438389f2-332d-2f70-cad4-784d7f54af9f@huawei.com> 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: <438389f2-332d-2f70-cad4-784d7f54af9f@huawei.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/16/26 13:40, Miaohe Lin wrote: > On 2026/6/16 14:56, David Hildenbrand (Arm) wrote: >>> >>> These non-atomics are defined and used because they want to avoid atomic ops overhead? >>> So I'm afraid using rcu read lock in these places would lead to unexpected overhead. >> >> It should be cheaper than atomics IIUC. Further, I assume that some pages could >> batch over multiple such operations (esp. page freeing path when we process tail >> pages). >> >> With !CONFIG_PREEMPT_RCU it's simply preempt_disable()/preempt_enable(), which >> is either a NOP or just adjusting the preempt counter of the current thread. Cheap. >> >> With CONFIG_PREEMPT_RCU we mostly increment current->rcu_read_lock_nesting. But >> there might be a function call involved (did not look into the details). So that >> variant should be slightly more expensive. > > I scanned the code and found rcu_read_unlock_special might be called in some cases. > Some expensive ops, e.g. irq_work_queue_on, might be called in some corner cases. > So the overhead of rcu read lock might be fluctuating. Right. Usually rcu_read_lock+unlock is supposed to be very lightweight, but that might not be completely the case with that PREEMPT_RCU thingy ... > >> >> We'd have to measure what an addition rcu read lock would cost in there. that >> should be fairly easy to benchmark. > > Sure. We can do that if needed. > >> >>> >>> I think this is a good idea, although there are some remaining issues. >>> But such race should be really rare, is it worth all this effort? Could we >>> simply aim to resolve, not to be flawless? I.e. could we simply check >>> and re-set the hwpoison flag at the end of memory_failure handling to >>> simply avoid losing hwpoison flag as a best-effort attempt? Would it be >>> acceptable? >> >> Hacky. Sufficient for the hypervisor to suspend the nonatomic-setting CPU at the >> wrong time to still trigger the same behavior. > > Right. hypervisor could make the issue easier to trigger... > >> >> I think, either we fix it properly, or we redesign hwpoison handling to deal >> with setting/clearing becoming stale at some random point in the future. > > I think your proposal, although there are still some issues to be resolved, is > nevertheless a good solution. We could also wait and see if anyone comes up with > a better one. I wouldn't call it "good" ... it's the only thing I was easily able to come up with :) The only alternative would be moving the hwpoison bit out of page->flags, storing it in a sparse bitmap or sth. like that. It would be a bigger rework and I am sure there are issues with that as well. -- Cheers, David