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b=VwOEf1yMXe96Q8PKjzX/91j8sVh665aI2y+5Y0LVVlTqa59ZzxnsqpuiV+lPJh7xy hp/j6q6dCpnWBF4zkNWvuAWUVRGK77NUas9YyofzOEjg99k82gtnT3w5fzYDTpHE13 whYrmxu1KdPAG2BxjYzcp/UnAHHSxLFZ6/4iHV5+b7QlNB5vGNyLuanxXGX9WI4+N9 GViRqRz1c5jBvZZD656cAKEfaTcLGC4LABq+Bo2drpmytDMH0pSzgqTMfXVs0EcXor b5oySlCYcDOxKEuwP+ndAMV+oJJpalzCLVBUoUUlTTrMtYOXb8MMzn3V1lve66+718 JFDYkl7W5qwWg== Date: Mon, 17 Aug 2026 17:29:42 +0100 From: "Lorenzo Stoakes (ARM)" To: "David Hildenbrand (Arm)" Cc: Vernon Yang , akpm@linux-foundation.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, zokeefe@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Vernon Yang , stable@vger.kernel.org Subject: Re: [PATCH v2 2/3] mm: khugepaged: fix folio is used after pte_unmap_unlock() Message-ID: References: <20260815051924.194810-1-vernon2gm@gmail.com> <20260815051924.194810-3-vernon2gm@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 6xfr1heyeceb5xcnow14a6sq7srrpe6d X-Rspamd-Queue-Id: 9CBD3100003 X-Rspamd-Server: rspam03 X-Rspam-User: X-HE-Tag: 1786984202-310916 X-HE-Meta: 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 QVWQt1sB OlxcVMIYaCb/je03SA9E8rACiCNZBr53L13KZsP1173qKpKm0FO7PWe46NQrIZMZDFbrRUV1/sR0bJ1VKS1/ArogqSQtbK1LKkfCi75yudSmXjchaD5qpwi1784QY2Oi2n/Vz1YtLM+LmITvYGyIm4BVBKV3PKM8glkFaBuw1Hs8um1G6x0sh0jLAHdaJXDyzWRNZe8w+tdSzVjMsUvEoizp2GdAxs/yOoS2CC/UrIUZGJCHVb6hvPFPM4A2/MgiudAEQtzmfyu+zklcmg7C1jY2FcgL8Pd6VNlf6mV8YElFZji4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Aug 17, 2026 at 06:20:02PM +0200, David Hildenbrand (Arm) wrote: > On 8/17/26 18:11, Lorenzo Stoakes (ARM) wrote: > > Same comment as 1/3 I don't see why we should be storing a pfn value used > > nowhere else just for tracing. > > I prefer it that way. Even if just for tracing. :) This is moot because you have to store the PFN for lifetime for museum-piece architectures. But anyway FWIW: Yes I agree accessing a now-invalid folio isn't great, but the reason I dislike this pattern is that you're tracking this state in a different way that now has maintenance overhead (if anybody reassigns folio or does weird control flow etc. they must now update 2 things and etc.) For the sake of CONFIG_SPARSEMEM and tracing for a value that is not at all intuitive as to what it means, that's not great. Let me go back and review this again accounting for the lifetime issue that I missed first time. > > -- > Cheers, > > David -- Cheers, Lorenzo