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 9223736997F; Mon, 23 Feb 2026 19:32:43 +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=1771875163; cv=none; b=fx34RUQKWAnbJcyfCPKNTcMFPxEmSgCEwP79K4VoMiOpMMHiyQjW5ycU4DhM9A44CP+r/g+9YN1sSDfp77pRpG3fzUrFV57aBNYpbqG9ploaaX/zp5mvNQ9Y7DMuzVlgARQxcZlR8zATh3PoMS9ZBBwAialBlu3w2BTx0/RK/3c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771875163; c=relaxed/simple; bh=AKjC73ZzhO2Cw8rIy39+iAnm5xnoxvOK6IN1Fx4kp+M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qhfSMLlTpeejBh27zI08Fdci86t+9lWqU/rfIXrYa6yrbIlw6D0p3gfMc4EqkUu4PZKHAPAB1te1KHLoh3yrB/1S48TdyT62tHTPWIER0uPCO5T4L+Sv4BiSYf3HOcddFXCSRFXsH1XHOOQg1H+1I1YnMxQuQjSq2Wq9R2O4gpo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pX58LaGJ; 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="pX58LaGJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1771AC116C6; Mon, 23 Feb 2026 19:32:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771875163; bh=AKjC73ZzhO2Cw8rIy39+iAnm5xnoxvOK6IN1Fx4kp+M=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=pX58LaGJiNo4oPkgO7P266+UDOIbdFCLvtF1Ak+cdkZcV98xkMMHwq3S3G16ESuPH dxixWT/2udHEy4HB/eCKI6Tcga6YzzEc99lE0y3C0SXq05By0Sp02EsNp5gsvRcTrP WBFVtPlHWbJwRPeKS1LVvlNf7SpghFS2C7+JC8fQLQj5rFkiymcCEeQMHoOX5eH4cr 69pFQd4V3NtTJvt8AX3Xbp7Utumi+O7Nke3XJd2Mt8V+jIIrd2Y0vlr+qrKbmXV/n4 mbTmUOf3VRy/b2v1pZHeLTLewp6ImQ2AB/dLu1tN7JG0DYjuN2jCKFk8FN4y5eTtUa 3KZMT+lCZs/4A== Message-ID: <9a972701-00b4-440d-8bc2-24b8dc469843@kernel.org> Date: Mon, 23 Feb 2026 20:32:34 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv6 08/17] mm: Make page_zonenum() use head page To: Matthew Wilcox Cc: Kiryl Shutsemau , Andrew Morton , Muchun Song , 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 References: <20260202155634.650837-1-kas@kernel.org> <20260202155634.650837-9-kas@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 On 2/23/26 19:18, Matthew Wilcox wrote: > On Mon, Feb 16, 2026 at 10:06:57AM +0100, David Hildenbrand (Arm) wrote: >> On 2/16/26 00:13, Matthew Wilcox wrote: >>> >>> You're right that different pages in the same folio can have different >>> zone number. But does it matter ... or to put it another way, why is >>> returning the zone number of the head page the correct way to resolve >>> this? >> >> How can a folio cross zones? > > I thought 1GB pages in hugetlb could cross zones? Maybe that used to be > true and isn't any more, or maybe it was never true and I was just > confused. I recall that 1G folios could end up in ZONE_MOVABLE (comment in page_is_unmovable()), but my memory is fuzzy when it comes to crossing zones (ZONE_NORMAL -> ZONE_MOVABLE). Freeing+reinitializing the vmemmap for HVO with such folios would already be problematic I suppose: we would silently switch the zone for some of these pages. When freeing such (boottime) hugetlb folios to the buddy, we use free_frozen_pages(). In there we lookup the zone once. Likely also problematic :) -- Cheers, David