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b=U7pLQunQoo58oGyCV174iJVpVlk4302aUvaZaF2d2peuHtth5HUV8I9ev9SuUCYQy hLakXm5wQ8sX9oBmEnEiM3Joh/N2VKytNBgq+LRmUqXgCTZvU5j9GqrNZfc+ceMBf4 oFd/ZchT19RJxat0qdSbE6SbIQGSUpPzGMPJABjMjiv/MiIdbUEwGTpq3pIH2JD/Mq QHxl6YERvgknA8G+t+/yVPUbmr8sD0YElsyzqqNKvnSryqia+9SxWMYBYTmG7HvZxa x5bnfFnbivosqEBXm68ZYPJ8F2kaFe8fAqhG9XjJkE4HpL1A4JuP7R/MXJtJS7pE7u Qj1QvT5yxu3Ig== Message-ID: Date: Mon, 10 Aug 2026 16:04:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 1/2] mm/memory_hotplug: optimize zone contiguous check when changing pfn range To: "Liu, Yuan1" , Oscar Salvador , Mike Rapoport , Wei Yang Cc: "linux-mm@kvack.org" , "Zou, Nanhai" , "Deng, Pan" , "Li, Tianyou" , Chen Zhang , "Zeng, Jason" , "linux-kernel@vger.kernel.org" References: <20260723084946.189392-1-yuan1.liu@intel.com> <20260723084946.189392-2-yuan1.liu@intel.com> <2cbd42e1-b5bb-474c-b0e7-ce3f46541891@kernel.org> <0b02ef3e-363f-4b49-a208-54cdfea56c75@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: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 9055A40019 X-Stat-Signature: ednemhhadrmadadonft4w916h8hrz7dr X-HE-Tag: 1786370660-730113 X-HE-Meta: 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 Hd5AMX6S qQalhfnvLoKw/40Qz4lhrv0l2RTwI9CnYAq0Yzcbz11wEIVxVPLWXDf7wQ9bq86art6TEtqXsNyrhfsWruntld1T+MsLpC4/zYghGdzL94cF7XrqNLkQaK9HGA6ASV2Q1N65p9UNoPhTUpAYFi01OcqfRMJ7VIn5jOG2t8nnv/FBC7L6zT5BbT3Q+4IzsYfjm01WIgZSxQ5wLqOqJjXfL2ghI/j3GXtkwgvUhzegNi22M5x+k0YTuj688tWTLMefdtyiueai+aRcDHAvqS9Iz7wwjGY+ckmJ7Qtw58/Odc58FU7hsI3Qi4iUW62BXByvw7oMKP3kqix5z5wBSJdXT6QghUjyvt3Ato5LIjlaW1nhNwHTYFhiDcdhO0rfeNC7+bQIn6HYHuHADohVBV6XMeZooKenEDrZmbt0anpzCXNKjH3A= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > > Hi David > > My understanding is that init_unavailable_range() initializes all > PFNs that satisfy pfn_valid(), but not all of them satisfy > pfn_to_online_page(), since some PFNs belong to subsections that are > not online. Thanks for reminding me. I think the right direction is to finally clean up the pfn_valid() handling. > > You previously mentioned: > > pfn_valid() says early sections always have a full memmap, so even invalid > subsections have a memmap. pfn_to_online_page() says an invalid subsection > cannot be online and its content must be stale. for_each_valid_pfn() follows > pfn_valid() semantics, and we use it to initialize memmap that is not going > to be online and account it as pages_with_online_memmap, which is wrong. > > The cleanest approach is to avoid allocating memmap for subsections, which > also removes the special early-section handling from pfn_valid() and > for_each_valid_pfn(). > > I also share the concerns raised by Sashiko in the analysis below [1]: > > Scanners like isolate_migratepages_block() will then blindly iterate through > the pageblock and access the completely uninitialized struct pages of the hole, > leading to functional errors or kernel panics when reading these zero-filled > structures via macros like PageHuge() or page_zone(). > > That's why we went with the current approach in v6 instead of your > earlier suggestion. I'd really appreciate your guidance on which > direction you think would be more appropriate. Let me take a stab at just having pfn_valid() / for_each_valid_pfn() respecting the subsection map. -- Cheers, David