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 44C20360749; Fri, 6 Feb 2026 10:42:18 +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=1770374538; cv=none; b=EZM0lGhe7NLfimW7Pv4nccG/j1o+4tY4XDq3WXeCwCGF2L6rHOMuBR3WM7tNpmKPb5LY2cT9YxF0kSRf43UsDoTHfExLHUjHfPE9CXSf80ToI8dCJvf9M68z0Su6J0e5ETF87qtHOuBzPr/2S7pZXX6DJTSxFcFV+2qP+Ef9Wak= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770374538; c=relaxed/simple; bh=X4ulH2AmDkCSg3stSWU0qmNiUtFh+CTtBIZg9eTnXM0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=QGGzfZRprMu08inFQcm7dJwG1oJBi7lD98YfxCZu4IKb2Dolge3G5il5VThGcF/uR2X0W0eZx4c2jG3MExUk6JZNTjTspD6a5gCQx+n/3KsFBLcCgjABts4d1XJU0sKkuK+xPs3ZUVQ8MYmTOGcuPGGXOty8l19qOXpr/xYbSow= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VTysHtsF; 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="VTysHtsF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CAA05C116C6; Fri, 6 Feb 2026 10:42:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770374537; bh=X4ulH2AmDkCSg3stSWU0qmNiUtFh+CTtBIZg9eTnXM0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=VTysHtsFbDZOc9nla0Q2lgBis/brgO6Tu+kf3ZjW0lCZpL1uJplM9eZTkXQhCcum2 UIQVwE1+A3z9/osnfEUHa5wrcr52RX4ivjXktLIzY5oVFuwODBON2ufk5tTgU6mn+R kRQjtEeQq2irifXeO/1G3CFjPn3stmMk/VvAx3qvWB8gbBiWAQl6yd0+kYztL1a+QJ eagSYMaSu7JIt54TiZMwJU+j3SfNPW7mc3mRGstPV06L/k2NOUTqClojWUxdl8PEiw /vumUJqdqpNOYsec/0f6JZTDY41m2mszc4Rs+BB36RPHPk/B4ZAjutUf6q1FNZNSrq eP+Xw8P8QMVAg== Message-ID: <0ecdd75e-ccd8-4217-a409-51da756ff1fe@kernel.org> Date: Fri, 6 Feb 2026 11:42:10 +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 17/17] mm/slab: Use compound_head() in page_slab() To: Kiryl Shutsemau , Andrew Morton , Muchun Song , Matthew Wilcox , Usama Arif , Frank van der Linden Cc: 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> <20260202155634.650837-18-kas@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: 7bit On 2/2/26 16:56, Kiryl Shutsemau wrote: > page_slab() contained an open-coded implementation of compound_head(). > > Replace the duplicated code with a direct call to compound_head(). > > Signed-off-by: Kiryl Shutsemau > > --- > > I am not sure if this open-coded version is intentional and required for > memdesc transition. Drop the patch if it is. commit 2bcd3800f2da1be13b972858f63c66d035b1ec6d Author: Matthew Wilcox (Oracle) Date: Thu Nov 13 00:09:15 2025 +0000 slab: Reimplement page_slab() In order to separate slabs from folios, we need to convert from any page in a slab to the slab directly without going through a page to folio conversion first. Up to this point, page_slab() has followed the example of other memdesc converters (page_folio(), page_ptdesc() etc) and just cast the pointer to the requested type, regardless of whether the pointer is actually a pointer to the correct type or not. That changes with this commit; we check that the page actually belongs to a slab and return NULL if it does not. Other memdesc converters will adopt this convention in future. I think using compound_head() is fine. For memdescs the function has to be changed to lookup the memdesc either way, and not go through the head page. Acked-by: David Hildenbrand (Arm) -- Cheers, David