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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Arjlk7Qt; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8E54E606A31D; Tue, 27 Oct 2026 13:35:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Arjlk7Qt Received: by smtp.kernel.org (Postfix) with ESMTPSA id 32BBD1F01825; Tue, 27 Oct 2026 13:35:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793108123; bh=DXXfHQerXMejJc/h/G8QmxS8zRqgGjGP7S6FBaiQJf8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Arjlk7Qt+D1zP0rhgU2TwlPbSPFeu6d5zAdGJpJ/2t/12E+ySLcT7HupgwQfHwTAR CKigig4dKa9KrHuLiIIcZnpXkxuj+2s0w/PHf6jcH05B8QTQjwpYAWFdaECJtjh3FY yHCoG1lLYscIjICHqfjZOpOBtu5IPgdZCTQS08TfhBNied3uoJHdEBCQw6sQEnQIHU W7k1Op/YP3pkt+lNUUPbs+5oMoWSQ6DmsbAqQzi0/kjOQsKXohLK5IxIzR8UjKgdRV oXJXb79cWZVJqnEf/ALW0tnCrC4p78g9GZJHxS+jZNchp2c2ip3sb69ZGxq1YGrBDS DyMPPLUExJ0yg== Message-ID: Date: Tue, 27 Oct 2026 14:35:13 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv7 13/18] mm: Drop fake head checks To: Muchun Song , Kiryl Shutsemau Cc: Peter Zijlstra , Andrew Morton , Matthew Wilcox , Usama Arif , Frank van der Linden , Oscar Salvador , Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Zi Yan , Baoquan He , Michal Hocko , Johannes Weiner , Jonathan Corbet , Huacai Chen , WANG Xuerui , Palmer Dabbelt , Paul Walmsley , Albert Ou , Alexandre Ghiti , kernel-team@meta.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, Dave Hansen , Andy Lutomirski References: <20260227194302.274384-1-kas@kernel.org> <20260227194302.274384-14-kas@kernel.org> <20261027110028.GH2668564@noisy.programming.kicks-ass.net> <070DDE5C-2183-4A8B-AC2D-891CAE15E581@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/27/26 14:13, Muchun Song wrote: > > >> On Oct 27, 2026, at 20:31, Kiryl Shutsemau wrote: >> >> On Tue, Oct 27, 2026 at 01:05:58PM +0100, David Hildenbrand (Arm) wrote: >>> >>> Right. Without HVO we would just corrupt pages in the single folio (which is >>> also not nice). >>> >>> I'm also questioning whether we need this RO protection all the time active. >> >> What do you have in mind? RO only under a debug option, or switching the >> tail page to RO some time after the remap? > > I don't think enabling RO only on debug kernels is a good choice. > > Within ByteDance, we once successfully caught memory failures using RO (because > we backported HVO, but some missing commits in memory failure caused write > operations on tail pages to persist). These operations triggered invalid writes > to shared tail pages. But would you have caught it with debug setting on in initial rollout / experiments? > > Under the old HVO schema, this invalid write only corrupted one folio, but under > the new schema, it corrupts all HVOed folios. Therefore, I personally believe > that for the new schema, the value of RO is even greater. But doesn't that mean that you would find serious bugs faster one way or the other? Silent corruption of any folio state is not good. -- Cheers, David