From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 A6049378D9A; Mon, 27 Apr 2026 12:32:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777293172; cv=none; b=XH3pLdqip/xK02P5wUH7W3p2/ai4nUPnY7rB75Jd2R+G8FbRXTtnBQHqe8KC0WMRbodigN0CWl7YFYtr8KMptYV4Bz0g+KkdkAytW1gFLxYsEuGh65pOLx/pIgRuz3JbnboKnQoNuYYc5HxIbvsw+W/ffZeu3NkQCRATysmi+UI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777293172; c=relaxed/simple; bh=xvYQlzxQ1hq53wWdlNPDCV/eKlBZfhodpK+RYNlKyPY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JNGmi5RSHczQg56ptZKMP+ozV5VU/gBcGcPZOXpXVJjdPckI93WYE/+S/p6NxI4W1LmsJG2wRWBeZWzluXVSkO3ZPY+aOPe6cEh/pCVAX5xOOKbFg9zDbKn1aa+kgQrbcejI3cv1EAFD8MNGA3MUQkRyt6N8UlzagI91oP41MKo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ip7GywcA; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ip7GywcA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8B3FBC19425; Mon, 27 Apr 2026 12:32:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777293172; bh=xvYQlzxQ1hq53wWdlNPDCV/eKlBZfhodpK+RYNlKyPY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ip7GywcA1FH/14ypAf5q1GhBaMpCJMHNJ0oNwZyx91OdfE7ATWTVoPYbEIH7xG399 KCazSQ5YkVf5Fw0qo9Y2P5/or6YxBg947RjhEPACI2CfczVh4hUxJESc4w0C9S1xoT oi9aqHS/7BEzQsQLf5oNBRAGWMRMLABkI2mLa91GPBaTCXdfmwUaqUu2u5JvvPOTI/ Zw50WOSUPMqUC7sOO00eBGgcD0aKmrJSVtzAqNShit8EgXCYqLfWhun4YWoZ12gdZI pITTuW5YaGT3GDvAl8NrF4gkCzYlwkt38O3AH7YXPj/zN+rdrAmTdtkTX6jCPTIJlB GRpeFz94yPTsw== Message-ID: Date: Mon, 27 Apr 2026 14:32:43 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 4/7] mm: add page consistency checker implementation To: Sasha Levin Cc: Pasha Tatashin , akpm@linux-foundation.org, corbet@lwn.net, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, skhan@linuxfoundation.org, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Sasha Levin , Sanif Veeras , "Claude:claude-opus-4-7" References: <20260424140056.2094777-1-sashal@kernel.org> <20260424140056.2094777-5-sashal@kernel.org> <4b961a07-b72d-4c8a-ab49-23f61ed12b53@kernel.org> <12985b32-88b3-47ab-8292-2e0ec6f5fbae@kernel.org> <3146ebcf-5649-44a7-aa21-163bf404c42b@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit >> But the real question is: how far away do these bits have to be in memory to be >> considered "independent" and not prone to the same corruption? >> >> 1 bit? >> 1 byte? >> 64 byte? >> 4096 byte? >> ??? > > The notes I have from the research side of things (which should be taken with a > grain of salt) are something along the lines of: > >  - ~79% are a single bit corruption >  - ~9% are row faults, so multiple bit corruption within ~8kb >  - ~4% are bank faults, so multiple bit corruption within ~512mb Interesting numbers, thanks! What are the other missing %? > > Obviously the numbers would be very different depending on usecase, hardware, > physical location (did you know bits are more likely to flip in higher > altitudes?)... Yeah, heavy cosmic ray apparently makes the problem worse. The 512mb case is obviously tricky to handle (and is very hw dependent). Placing bits at least two pages apart could be done more easily. > >> "Embedding both in page_ext means a single fault could >> corrupt both the tracking data and its redundant copy in the same >> allocation region." >> >> I might be wrong, but isn't that the case for any such fault, as you don't 100% >> know how the DIMM is organized internally? >> >> Do we really expect that a MCE event would, for example, very likely corrupt two >> neighboring bits, or two bits in the same byte etc? What are the odds that we >> care? > > For something like a datacenter deployment I'd agree with you - the odds are > too low to care. For an unsupervised self driving vehicle, where there's no > human (locally or remotely) available to take over, I'd like the odds to be as > low as possible :) I thought that people usually use special RT OSes (with proven logic etc) for any safety-related systems. Using Linux on the core safety system sounds ... scary. But, I'd expect corruption of other data (user pages? page tables?) a much bigger problem than page al locator metdata? What am I missing that this here is -- in context of the bigger problems there -- a thing we particularly care about? -- Cheers, David