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 D43D01E1C02; Thu, 5 Feb 2026 13:52:36 +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=1770299556; cv=none; b=pI8cYO7vKDH3lX5s1kN84Z8eo3Fazt2HCIaqMWsFiIerxWLbCTX49b7KG7yI/oGWvbeVJwPezua/9oP3uW4oac0LZhb/Ad2Cj2EJbbcQ0iY9k4GipmB46MSDZKaBZGqGnI8kllXed1LAmHcdxDbSUCag68Tva+wSZJM0dLY3boM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770299556; c=relaxed/simple; bh=ZKRLdfY8j+3tSCOhu7lXU/4i+dGzR6BqlTNQ2fMayes=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=iQKpBU/X2nkMjH5a/bnNSyRjGjXYbrgjkHv+ALLylUaQlYCOFOG6gUKfVg5Z6gYLuUDaF1ZhT1osID2lLP/MdsDHQX5DHn+nFsCjFznoLHx0ETRkEsfBDgVmdQNjhPmOq39M47xgRkU3W9+rkLOskhNp263XBkGwGxOapB7HxlY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PABi8CWR; 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="PABi8CWR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65A40C4CEF7; Thu, 5 Feb 2026 13:52:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770299556; bh=ZKRLdfY8j+3tSCOhu7lXU/4i+dGzR6BqlTNQ2fMayes=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=PABi8CWRapGvnWwD6wZA0gWf2kzC85OADNDNQ+5ZsMgQULKe7P+pTF23HBeTY30cO KncdahQa08a9SOtjZiIXcDaq0NA2sMxkMtq3Vx8YJS6VwVo5vg1hX5RPIsKZbe7TER gHSDA6A11s1XLgW1RnDZgeE6tIS0vcfjGeqvQY7P1Apfb+CW9XPlcRH/QVyqUWwWrS p/zLhgjBcOqqzYiOQ7v+xph6zhf1Kd9yvckyXNT4+DjrG0tCeCWk/n1KFI0jzBgM8r YpeBP8DHGBG3KF0r/0gQlrl5i9l0jcR/amYMxz8bYX5bGsWBk7+qINuqHd4b9uJv6K O8YXH7FHEUCEQ== Message-ID: <460457b0-64c5-48a2-a5e4-d88ecc222884@kernel.org> Date: Thu, 5 Feb 2026 14:52:27 +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 06/17] LoongArch/mm: Align vmemmap to maximal folio size To: Kiryl Shutsemau Cc: Andrew Morton , Muchun Song , Matthew Wilcox , 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> <20260202155634.650837-7-kas@kernel.org> <2ce0e684-de54-43ec-be7d-c58bbffb3f4e@kernel.org> <062900fa-6419-4748-81d1-9128ce6c46d0@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2/5/26 14:43, Kiryl Shutsemau wrote: > On Thu, Feb 05, 2026 at 01:56:36PM +0100, David Hildenbrand (Arm) wrote: >> On 2/4/26 17:56, David Hildenbrand (arm) wrote: >>> >>> >>> Same comment, the "MAX_FOLIO_NR_PAGES * sizeof(struct page)" is just >>> black magic here >>> and the description of the situation is wrong. >>> >>> Maybe you want to pull the magic "MAX_FOLIO_NR_PAGES * sizeof(struct >>> page)" into the core and call it >>> >>> #define MAX_FOLIO_VMEMMAP_ALIGN    (MAX_FOLIO_NR_PAGES * sizeof(struct >>> page)) >>> >>> But then special case it base on (a) HVO being configured in an (b) HVO >>> being possible >>> >>> #ifdef HUGETLB_PAGE_OPTIMIZE_VMEMMAP && is_power_of_2(sizeof(struct page) >>> /* A very helpful comment explaining the situation. */ >>> #define MAX_FOLIO_VMEMMAP_ALIGN    (MAX_FOLIO_NR_PAGES * sizeof(struct >>> page)) >>> #else >>> #define MAX_FOLIO_VMEMMAP_ALIGN    0 >>> #endif >>> >>> Something like that. >>> >> >> Thinking about this ... >> >> the vmemmap start is always struct-page-aligned. Otherwise we'd be in >> trouble already. >> >> Isn't it then sufficient to just align the start to MAX_FOLIO_NR_PAGES? >> >> Let's assume sizeof(struct page) == 64 and MAX_FOLIO_NR_PAGES = 512 for >> simplicity. >> >> vmemmap start would be multiples of 512 (0x0010000000). >> >> 512, 1024, 1536, 2048 ... >> >> Assume we have an 256-pages folio at 1536+256 = 0x111000000 > > s/0x/0b/, but okay. :) > >> Assume we have the last page of that folio (0x011111111111), we would just >> get to the start of that folio by AND-ing with ~(256-1). >> >> Which case am I ignoring? > > IIUC, you are ignoring the actual size of struct page. It is not 1 byte :P I thought it wouldn't matter but, yeah, that's it. "Align the vmemmap to the maximum folio metadata size" it is. Then you can explain the situation also alongside MAX_FOLIO_VMEMMAP_ALIGN, and that we expect this to be a power of 2. -- Cheers, David