From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta0.migadu.com (out-171.mta0.migadu.com [91.218.175.171]) (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 2C0F036D9E9 for ; Wed, 1 Apr 2026 07:29:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775028555; cv=none; b=jOq+4XGVeZp1yMKejSAYZSfwV0KJ4nDdOQ/MiKgmv0OfcCP5XP/mp/qzNQnWa6XNvmc02PyDFiV/xtbVxg7kzHPbVxMkQJHq5cNqkie+UlIzB5Gv1q/ZNCiU+XwqgmsskU9TP5Wcp4WMNsJDnYL7n/f4q1rNrPlmyngRd56gJ2A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775028555; c=relaxed/simple; bh=Ms55ZFkes3Y+kx1lD6phlNGkvL5LMzF0B7MCfjTlpfw=; h=Content-Type:Mime-Version:Subject:From:In-Reply-To:Date:Cc: Message-Id:References:To; b=ZKH0QDQWwu6lXoGzhyOrinh8x3UOR3g1mqu+r5YaRgFjGrKkjIQbVYuLxlSTeQxzkAL7wXE8UdsYx8v5mRhGBd5R3q2JBEKX6yluIa4r/A3YZS2rfxVOTrvOm4INHnHdv5MjmQp7v3rzn/Ja0Gx2ACteO/arOSR8QnwuQOrLKv8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=LLod/Tfq; arc=none smtp.client-ip=91.218.175.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="LLod/Tfq" Content-Type: text/plain; charset=utf-8 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1775028551; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ms55ZFkes3Y+kx1lD6phlNGkvL5LMzF0B7MCfjTlpfw=; b=LLod/Tfq6gF9cdENfrE1ZqGU4Da6Xhz7DV9NTvyeErzj3L6ugLvZejm00vhy5wKdLy1QNA TaKTET2EEoLVvi6mXIrrBUzDIeJ+MjKjiXcZazOj5ESL/smM9CyafXrlSFHkMVGdfzk5Nw O+RjpKOcXE0rJbaaJ0nDvZ6a75L0Mj4= Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3864.400.21\)) Subject: Re: [PATCH] mm/sparse: fix BUILD_BUG_ON check for section map alignment X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Muchun Song In-Reply-To: <1f8d0cd2-c990-4597-bf47-5a8217acc464@kernel.org> Date: Wed, 1 Apr 2026 15:28:36 +0800 Cc: Muchun Song , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Petr Tesarik , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <6B06FA9A-F332-4BE8-B80A-BB869802600F@linux.dev> References: <20260331113023.2068075-1-songmuchun@bytedance.com> <32789381-f860-4b60-a1e1-4c97f6ed08b1@kernel.org> <7C90E910-D229-4F60-A62D-E893A89D58F2@linux.dev> <1742503A-F912-4AB6-AAF6-6CDB06829024@linux.dev> <9fddd112-e304-4ce1-b3f0-a4b133fcb281@kernel.org> <1f8d0cd2-c990-4597-bf47-5a8217acc464@kernel.org> To: "David Hildenbrand (Arm)" X-Migadu-Flow: FLOW_OUT > On Apr 1, 2026, at 15:26, David Hildenbrand (Arm) = wrote: >=20 > On 4/1/26 09:23, Muchun Song wrote: >>=20 >>=20 >>> On Apr 1, 2026, at 15:08, David Hildenbrand (Arm) = wrote: >>>=20 >>> On 4/1/26 06:01, Muchun Song wrote: >>>>=20 >>>>=20 >>>>=20 >>>> Sorry, I misread it earlier =E2=80=94 I thought it was about the = memory >>>> section size, but it's actually about the memmap size. Let me = respond >>>> again to your question. On the powerpc architecture, when = PFN_SECTION_SHIFT >>>> is 6 and PAGE_SHIFT is 18, it does seem that the memmap of a memory >>>> section would be smaller than a single page. >>>=20 >>> Right, and I am saying we don't care about that and do not support = it. >>>=20 >>> For example, most vmemmap code I am aware of relies on a single = section >>> covering full pages. >>>=20 >>> So I don't think this patch here adds any value, except faking that = we >>> might be supporting something we don't? >>=20 >> Got it. >>=20 >> My original motivation was simply that when I read this part of the = code, >> the comment felt a bit off to me, so I just fixed it casually. But if = it >> ends up creating the impression that "we might be supporting = something >> we don't," as you said, then I'm fine with dropping this patch. >=20 > Can you rework your patch to only simplify the comment, and to clarify > that we always expect a single section to cover full pages? No problem. >=20 > --=20 > Cheers, >=20 > David