From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 99D92C43458 for ; Tue, 30 Jun 2026 06:30:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6F6696B00A4; Tue, 30 Jun 2026 02:30:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6A6DF6B00A5; Tue, 30 Jun 2026 02:30:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 570AC6B00A6; Tue, 30 Jun 2026 02:30:23 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 2B81B6B00A4 for ; Tue, 30 Jun 2026 02:30:23 -0400 (EDT) Received: from smtpin03.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 871241203C3 for ; Tue, 30 Jun 2026 06:30:22 +0000 (UTC) X-FDA: 84935604684.03.7EEEE4B Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf16.hostedemail.com (Postfix) with ESMTP id 8D55018000A for ; Tue, 30 Jun 2026 06:30:20 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ftiz5Kz6; spf=pass (imf16.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 ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782801020; b=wsGoXxkhhQ4SP7Pmlw+i0GyzlRLiZIrQlSC2YhhbfMpeO8RXrU82ty5F/k67+9Ae6IKGO0 a2fw+qCiokWdou1yMKMWzZOTbEPFPD3Nx73RSFJWI5zrbXexNJO4knHDCXi6NoOXvr9vp0 B5LkRskQ/2+PKsZwMW7Q1yDPgKD9JpY= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782801020; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=KOV37TH76GArpnwbguSBuDZgeS0U+NTFaarv2sWby3M=; b=Ulg5rUCuQKQOGRozpAGmKcuw9YC06dkHoJEHyToKmRYIuByjnUP7okpnbAt6BJFBW30Plo SHrMe7lrqQN+SvIxN+A4GgqYWzeEWnc3e7I6Gib76T7BiMkOgCV0iqX+iTl+4Wnf3deNPU bvrC1QY7w8wKYFULlSnWaJYNbv2FJjc= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ftiz5Kz6; spf=pass (imf16.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 BA0D4435B0; Tue, 30 Jun 2026 06:30:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 00E041F000E9; Tue, 30 Jun 2026 06:30:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782801019; bh=KOV37TH76GArpnwbguSBuDZgeS0U+NTFaarv2sWby3M=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ftiz5Kz61TgJ9Z1X5mAqhTLE3tOs3XuQ1Rr4KSSWFuOuVlK7xUruIm7ycl2jg5JRE SDacCiXIvEURjJE+Z0rC6xCDqxC8uFR2rHCDSJTrUv2diaedaU7gJedwjzl+rMPZq0 1703isnm/mhq8236+fb+8QwQKLfiLdJJHAwN3G5+GfSnhDJIoAbJ4zupTAKrtmvhLt Pe30hMlArDdkJGVJB2A5JlZ5trPl8lDZXW4V/3N/hqg7zygXEeGOQCbLbRKeQxbH6/ F20w52pdxXvcHCK6QvOwOFD+LTjbggQZnnOJ+JpYEx1Ts4dsNHnEixC0RgCiYuCufI D6xPtHSoDGzQw== Message-ID: Date: Tue, 30 Jun 2026 08:30:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] mm: memory-failure: fix HWPoison flag race with non-atomic page flag ops To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, Miaohe Lin , Naoya Horiguchi , Andrew Morton , Oscar Salvador , Andi Kleen , Hidehiro Kawai , Rik van Riel , Vlastimil Babka , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Hao Li , Kiryl Shutsemau , Byungchul Park , linux-mm@kvack.org, linux-cxl@vger.kernel.org References: <0b5f8b4b-d7dc-4b79-9555-a5b36265f3a9@kernel.org> <20260629030657-mutt-send-email-mst@kernel.org> <4f5ba5d6-246c-4430-9737-e8dd8e4c5142@kernel.org> <20260629092856-mutt-send-email-mst@kernel.org> <54c8cbee-9b26-458c-93ba-5aa594f5d1e8@kernel.org> <20260629174225-mutt-send-email-mst@kernel.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: <20260629174225-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: rnmtpubkg3ct13f7ppbpreah6rd5fkq4 X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 8D55018000A X-HE-Tag: 1782801020-743389 X-HE-Meta: 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 xb4whYoU GxSkH9Gz5fRMTLv71SlBTDEFPouLUurf99t5RE1t+Da++9NSBuNOkeKLfddytbB34LEn8P3sAkqv3XSnYTzCM/g/FomH1zsuv0F2o3qqE0O5hIYP1NwYxHKt8L6mq2mJrjLfVnp0KBdLIUwLaqgYpuZgpHb1biodsRptJUwoUXkpEIHRY9IzBpaqsE80GBz5HshCj6WpuG3hHMIyG9qM1+kMpStJwiDf0GBUgvN7Xi0+iE4Z4zfjoUeXOITAw2GrDTy8dOdH8KsZaFawPn0oVqBpnIawb5bxMRAErsSk6DmK41bHoG5H8sz4rPADBrVY4jrLnlMSlO26wwDwOVz0fYWVgLg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/29/26 23:50, Michael S. Tsirkin wrote: > On Mon, Jun 29, 2026 at 11:22:11PM +0200, David Hildenbrand (Arm) wrote: >> [...] >> >>> >>> And again, I'm really not sure fixing a theoretical race when memory >>> is failing is worth slowing the world by 0.1-1% for. >>> >> >> Fully agreed. I was hoping RCU was cheaper (I mean, we were once told that RCU >> read side locking is essentially for free ... well in some configs :) ) >> >> The question if we could optimize it reasonably enough ... >> >>> >>> From what I saw in my testing, if we allocate 4k pages >>> it's hidden by the overhead. With hp and thp it's measureably >>> worse than rcu on !preempt config. >> >> ... for example, by doing the rcu read lock + unlock around the >> >> for (i = 1; i < (1 << order); i++) { >> >> loop on the alloc path. > > Is this different from what this patch is doing? Ah, I missed that we batch this already. We could make it include the page_cpupid_reset_last(page); page->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP; As well, to reduce from 3 to 1 locks. So I guess there is potential for optimization. [...] > >> I concluded, similar to Andi, that stop_machine() is too big of a hammer. >> >> I wonder if something could be built out of preempt_disable() and sync SMP >> calls. hmm :( > > rcu_lock is basically same as preempt_disable if rcu is non preemptible, > no? Yes. See my other mail, I learned that preempt_disable() should likely just do for our use case. So the preemptible RCU case would not matter. I assume that's as good as it gets. 1) Use preempt_disable/preempt_enable to protect 2) Batch as good as possible in the page allocator If the overhead is then still noticeable, there is not a lot we can do to handle this cleanly I'm afraid. -- Cheers, David