From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (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 6A4F022AE4E; Mon, 7 Apr 2025 08:59:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.95.11.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744016395; cv=none; b=XhLvnoFrg6ben7uPWEGIpXekNWk587LnqXMo5LMxUcNv3WejS1b8UeUJGGP2ne6DBzgCX10b0uXBqwU6kPVHvK+CrHVH/sdebKTud2YFK3gEOnRozDlHgzWjBElfSCSU389m8Ibmiy9y7l0Vd33IocgzEuEQmKJIbu/FB7mzoRw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744016395; c=relaxed/simple; bh=/KZr0izSTAZMM0jVYPGx+EQyA76KAy1RBD0L3EszOIk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mdTcI6fiNiE+nXwqGpp9oFgLzZa+afKKeHwoXx7oBoX/OYfiTl55s9B4Cw9vqM4HyC/c06l2/8/DYSafsCWaKekgTdw65CgNHYLvCl2hvnRkRrmAfiXJ1Om3DKlQXqhfCHnH2mdoqdoh17xMd/HNFQSQH3dQGpV+FFNoomRO6pY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.client-ip=213.95.11.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de Received: by verein.lst.de (Postfix, from userid 2407) id 2DB0768BFE; Mon, 7 Apr 2025 10:59:44 +0200 (CEST) Date: Mon, 7 Apr 2025 10:59:44 +0200 From: Christoph Hellwig To: Muchun Song Cc: Huan Yang , bingbu.cao@linux.intel.com, Christoph Hellwig , Matthew Wilcox , Gerd Hoffmann , Vivek Kasireddy , Sumit Semwal , Christian =?iso-8859-1?Q?K=F6nig?= , Andrew Morton , Uladzislau Rezki , Shuah Khan , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, opensource.kernel@vivo.com Subject: Re: CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is broken, was Re: [RFC PATCH 0/6] Deep talk about folio vmap Message-ID: <20250407085943.GA27481@lst.de> References: <20250327092922.536-1-link@vivo.com> <20250404090111.GB11105@lst.de> <9A899641-BDED-4773-B349-56AF1DD58B21@linux.dev> <43DD699A-5C5D-429B-A2B5-61FBEAE2E252@linux.dev> <6f76a497-248b-4f92-9448-755006c732c8@vivo.com> <35D26C00-952F-481C-8345-E339F0ED770B@linux.dev> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <35D26C00-952F-481C-8345-E339F0ED770B@linux.dev> User-Agent: Mutt/1.5.17 (2007-11-01) On Mon, Apr 07, 2025 at 02:43:20PM +0800, Muchun Song wrote: > By the way, in case you truly struggle to comprehend the fundamental > aspects of HVO, I would like to summarize for you the user-visible > behaviors in comparison to the situation where HVO is disabled. > > HVO Status Tail Page Structures Head Page Structures > Enabled Read-Only (RO) Read-Write (RW) > Disabled Read-Write (RW) Read-Write (RW) > > The sole distinction between the two scenarios lies in whether the > tail page structures are allowed to be written or not. Please refrain > from getting bogged down in the details of the implementation of HVO. This feels extremely fragile to me. I doubt many people know what operations needs read vs write access to tail pages. Or for higher level operations if needs access to tail pages at all.