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 3D5FA34FF53 for ; Tue, 6 Jan 2026 20:04:02 +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=1767729843; cv=none; b=OChxcUr+6Alc5FusQdOa+0qiTUczPksq8EYe3/xjuwi/WMukSKktwWVU2OJpfkJIQgm0IQ7Sm9ZuBdpPxs/o/YqJ6wg0JL72OG9F0ltpo3qStpQYz3tjkR6oFtygtsR9ka3nKs8erqN5uIHvNV9M1nKhJGnFw1ZLkEnG9++NJvY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767729843; c=relaxed/simple; bh=Q6xGZJmPaIERTQ/PbYnzfWP+ZBaqkIj/1xfOlvYbOCg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hfk6qksbaiK9/IVGVFnl1LkOkvVPHiRQfOkofWabi7kwa4KlaCG8po6m+NAbmvmSIWV0iWG+Pu5rUJ1p71M0vAcoDddtR1Ni5pBGodCzdHNL9ywntR+7VXtvu3gcwDFKhKresTOylRXF4ImVtKdnDi5wOabr6Hjna+EWXtvNRrg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VJJjaibs; 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="VJJjaibs" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3813BC116C6; Tue, 6 Jan 2026 20:03:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767729842; bh=Q6xGZJmPaIERTQ/PbYnzfWP+ZBaqkIj/1xfOlvYbOCg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=VJJjaibsIHpdBm9Dc8E7uYrAZfg7FXmoqZrc0K/k2QtFykZticTsazwBOnHIMOhN1 JNCvpGF5V/91NM2XYkj7sAgNZOQwpYcROcU62wtvWRwwYud1tKC3dPpgZyWhC6xDDe aBy2rN//OuG017ao4sgjFjv91qhvkK/umSd8ktWl0mrGZ3fPqA376MyJ7PS6zIIA5U cjq13EaB6MG7z/08sa16NmgtqWzQv4TufYJMviM6VgRkYPNG0f/tEMQ/1aFqCzqvmq BBsb4kDo/0AFFiKGg6VTqQv99ZPgPo+BalmB9qbIUvIWc8TWurjbJaUW+39s6CF4C3 PxPNyi/cORVDg== Message-ID: <857be078-1464-4e29-979d-0459cad8508b@kernel.org> Date: Tue, 6 Jan 2026 21:03:56 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 1/2] mm/memory hotplug: fix zone->contiguous always false when hotplug To: Tianyou Li , Oscar Salvador , Mike Rapoport , Wei Yang Cc: linux-mm@kvack.org, Yong Hu , Nanhai Zou , Yuan Liu , Tim Chen , Qiuxu Zhuo , Yu C Chen , Pan Deng , Chen Zhang , linux-kernel@vger.kernel.org References: <20251222145807.11351-1-tianyou.li@intel.com> <20251222145807.11351-2-tianyou.li@intel.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/22/25 15:58, Tianyou Li wrote: > Function set_zone_contiguous used __pageblock_pfn_to_page to > check the whole pageblock is in the same zone. One assumption is > the memory section must online, otherwise the __pageblock_pfn_to_page > will return NULL, then the set_zone_contiguous will be false. > When move_pfn_range_to_zone invoked set_zone_contiguous, since the > memory section did not online, the return value will always be false. > > To fix this issue, we removed the set_zone_contiguous from the > move_pfn_range_to_zone, and place it after memory section onlined. > > Function remove_pfn_range_from_zone did not have this issue because > memory section remains online at the time set_zone_contiguous invoked. The description is a bit hard to follow. Let me try: "set_zone_contiguous() uses __pageblock_pfn_to_page() to detect pageblocks that either do not exist (hole) or that do not belong to the same zone. __pageblock_pfn_to_page(), however, relies on pfn_to_online_page(), effectively always returning NULL for memory ranges that were not onlined yet. So when called on a range-to-be-onlined, it indicates a memory hole to set_zone_contiguous(). Consequently, the set_zone_contiguous() call in move_pfn_range_to_zone(), which happens early during memory onlining, will never detect a zone as being contiguous. Bad. To fix the issue, move the set_zone_contiguous() call to a later stage in memory onlining, where pfn_to_online_page() will succeed: after we mark the memory sections to be online" Now, there is no need to add the handling to mhp_init_memmap_on_memory(). Note how mhp_init_memmap_on_memory() in memory_block_online() is always followed by online_pages(). So, it's sufficient to move it after the online_pages_range(). I would also add a comment there saying something like: /* * Now that the ranges are indicated as online, check whether the whole * zone is contiguous. */ Can we find some Fixes: tag (which commit introduced the regression)? Likely we want to CC stable. -- Cheers David