From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 6619237DAC2 for ; Mon, 29 Jun 2026 20:44:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782765866; cv=none; b=WccZy8Rj+UMX1aCdjd1iBUVa8PElky1SKwgFGltSSoMUuHy3GFA1eWt97w8xOoXVdscnyjzs1jVUKWLBQnLJOJfqFi3IvEzb2SHRT+J86gEKcdo5oi0K9GN9GMhLZL0ea0WoCSpHEjuanVSeK+At5opk/ibgL4Klz2ezMTRjt2U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782765866; c=relaxed/simple; bh=8vU9Enikwm2aJC0sPAErMK2X1JZkxrkRDio+9c/Jiwo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gcXaFIvYAMPrggbf1tShho9/N5SUmPLVY2zYXDsMYpkdjGD5hpKZYPSaBvPG2rPHiMiTn3GULpL8kNRZMv1njDR2SYunwPNm64NYCDv0lZeotP1wLv5hD4GwQg+G5YK8aaXmyL9WPSTECSrTPBgJnPUcbdN+WrjUdKktQ1OldU8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=XmAyMmMw; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=SlfP23yy; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="XmAyMmMw"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="SlfP23yy" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1782765864; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=TOQpLe5g2es+HuSRD8vnoaoM9ObrVUNQWd1XrTtB+E4=; b=XmAyMmMwmftSK49Agi47OtWX5GZNhuw9l6LW1rjMEa2OwC2biKy2S2MgT337avMjg2md1Q /cF/zPPWGsZhPcO1fbhfw+J02HOtkB9TEuVHA9smdE6+YAlValOUS63tmp6Tq62+sJGvE0 DD30B9PZ3OAdl/qUK3b0tvJPYMEHxmc= Received: from mail-dy1-f197.google.com (mail-dy1-f197.google.com [74.125.82.197]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-118-lmTC9kgOPbGjlAVLKPgjbg-1; Mon, 29 Jun 2026 16:44:23 -0400 X-MC-Unique: lmTC9kgOPbGjlAVLKPgjbg-1 X-Mimecast-MFC-AGG-ID: lmTC9kgOPbGjlAVLKPgjbg_1782765862 Received: by mail-dy1-f197.google.com with SMTP id 5a478bee46e88-30b877ee493so5718474eec.1 for ; Mon, 29 Jun 2026 13:44:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1782765862; x=1783370662; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=TOQpLe5g2es+HuSRD8vnoaoM9ObrVUNQWd1XrTtB+E4=; b=SlfP23yy8OU6waK+/zNpOkDwFFHYQ7vO8b0Lc0BMMKoqzqvayVZpGe84A/1qQIcE61 hAC6mnNcBrmeppo7vuUtFDmq270+u5jfz/cK74d4csh59Xsh/pcxEeSu/PpgkD6LeW5k 9KCxlBm0k/ce9BmnrG7D0uEMK1geqrLh9PZlZpNbdJ6RO8vtwzjZAjGpUlBIkqoyMF9S IBX0urJ2p4yQppFpKjBB58XqkPj8ykGE9lvwhjEPRiPjx4Jeo+ggLblsJkjujCEZ09O2 CcnFDCU/xiAn3KGg8BUe2IcDTUcTuE9CPGpTwALO5uIKrNTbQad8WuG/iGr5iAcuzynh un6A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782765862; x=1783370662; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=TOQpLe5g2es+HuSRD8vnoaoM9ObrVUNQWd1XrTtB+E4=; b=EDTu9PdFZwGScndf0k9Y5W7EqVx2y0BuDBPtQuHibHj46jx8/Z4xDtVOOSMqTeIH4K HVbJ3z39DbeM48fkbM5dPQMkSYtOtScXw9xSkx8GPUvN6E+i4QkAl2AmblJtuic8ZYtz 0N2KkfkC7uM3GTM0h64zNuKxvhOp+4laDeWovxgKyacVq6KR6zR4SztqN2xLBQ5tNp0l mQOM7y6yoNEaI0cBhvSFJGVLNxdH3UwX8LszQkOk6yjJSwpm7zdGDPGdnGdwgne3Haqi Q0knX5hd7nqcR9F4HSRpezlMNn3HK6EpcqQjunB4yTrD76ylGsmG5yjsmbP39AchrW5P 927g== X-Forwarded-Encrypted: i=1; AHgh+RrGycD+j41CKCwIYh8PDtlk99D5Dqp5G4dE4Rh5AiTffbtPXkFcyUFYCl88Xb6wXX3u/wRrKv/Kn0eGxVo=@vger.kernel.org X-Gm-Message-State: AOJu0YzJNMwmtFBzR25BaGFGdPl3ABe17lmU9EjyIbsynf7Kzpwa+gxS Xl0sU2+6dIprBHMmtmpAf58/FFnCLezMcH3vLfZgD6ay944xzcbE+l5y2NoGJOPR+9wMAWeSKuj l50jJpMa01v7VfH0RfUXEml2iFemVat77kSDyXyfMCq5bD75vNoRxt2Bgkr4QMn3kEQ== X-Gm-Gg: AfdE7cleQ+PY156W6It9JG3UjNMoa/3f02HqX/24bdNbZ1jbo9xQ8ulNAtXmBIvGD+3 TE5cm86RES3mDYc355xxWPJ7qFbVhjPrC3W3AgBbKalukLbPBvk4ac7SET3BLsDw7IWlakuAzxJ 9QblH7G3l2bOJGFR6vnEdX55SS59GhfPlMoJg93I8Eo8jqUPRTRDs0fSji8yCtPs+zC6/dPdMjZ Ds91KjJvG5DuIT7JueKb4sYP+7hx+8BiTg9YQeFdkj9BEeC2oyrNaCir6FjmwFQUJu0KZMSOAML NtFSRAAr8ogyMGcKBrvahY7ZPwM99QvnK4SXMToUQzhgYPAFhAGXwcmc8tkQq5t/MMjUOBFpVWz WJkam7Owy0rA/Cq/8dVk3tNy772byTOMa X-Received: by 2002:a05:693c:8948:20b0:30c:ab96:7307 with SMTP id 5a478bee46e88-30ee18ba288mr436354eec.22.1782765861523; Mon, 29 Jun 2026 13:44:21 -0700 (PDT) X-Received: by 2002:a05:693c:8948:20b0:30c:ab96:7307 with SMTP id 5a478bee46e88-30ee18ba288mr436310eec.22.1782765860825; Mon, 29 Jun 2026 13:44:20 -0700 (PDT) Received: from redhat.com (IGLD-80-230-85-71.inter.net.il. [80.230.85.71]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-30ee2f5e4dcsm857053eec.5.2026.06.29.13.44.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 29 Jun 2026 13:44:20 -0700 (PDT) Date: Mon, 29 Jun 2026 16:43:56 -0400 From: "Michael S. Tsirkin" To: "David Hildenbrand (Arm)" Cc: Andi Kleen , linux-kernel@vger.kernel.org, Miaohe Lin , Naoya Horiguchi , Andrew Morton , Oscar Salvador , 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 Subject: Re: [PATCH 0/2] mm: memory-failure: fix HWPoison flag race with non-atomic page flag ops Message-ID: <20260629164258-mutt-send-email-mst@kernel.org> References: <20260629033608-mutt-send-email-mst@kernel.org> <20260629043417-mutt-send-email-mst@kernel.org> <20a5dfd4-b3c7-450a-8a70-08d0345aade4@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20a5dfd4-b3c7-450a-8a70-08d0345aade4@kernel.org> On Mon, Jun 29, 2026 at 07:04:25PM +0200, David Hildenbrand (Arm) wrote: > On 6/29/26 18:54, Andi Kleen wrote: > >> However, this was a basic test, when allocating 4k pages. With 2M hugepages: > >> > >> insns/iter cycles/iter > >> ------------------------------------------------------- > >> base 20758 +/- 12.5 191208 +/-1946.6 > >> rcu 20785 +/- 3.7 197108 +/- 132.1 > >> atomic 20727 +/- 6.4 204591 +/- 160.2 > >> > >> rcu vs base +27 (+0.13%) +5900 (+3.09%) > >> atomic vs base -31 (-0.15%) +13383 (+7.00%) > >> > >> and even with THP: > >> > >> insns/iter cycles/iter > >> ------------------------------------------------------- > >> base 27220 +/- 2.8 192151 +/- 483.3 > >> rcu 27248 +/- 30.1 194159 +/-2746.6 > >> atomic 27186 +/- 3.2 200526 +/- 746.2 > >> > >> rcu vs base +28 (+0.10%) +2008 (+1.04%) > >> atomic vs base -34 (-0.12%) +8374 (+4.36%) > >> > >> > >> needs more thought. > > > > Well the alternative is to not bother with RCU, but just wait a bit and > > check if the bit stuck and repeat if needed. While that could in theory > > livelock it is extremely unlikely (especially if you add a bit of randomization > > to the sleep) > > We discussed that a bit already. Hypervisors make it fairly unpredictable how > long you would actually have to spin. Way I see it, this is not the issue. The issue is it does not fix the race: CPU1: read flags CPU2: test and set test and set #2 - sees it is set CPU1: write flags clearing the bit > -- > Cheers, > > David