From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4ED21C54F4C for ; Tue, 28 Jul 2026 12:58:52 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 09C4D10E591; Tue, 28 Jul 2026 12:58:52 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="A74PjBdP"; dkim-atps=neutral Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id AAF4610E591; Tue, 28 Jul 2026 12:58:50 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 3CB57415C3; Tue, 28 Jul 2026 12:58:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 91F4E1F00A3D; Tue, 28 Jul 2026 12:58:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785243530; bh=Q62HDP0Erg3czKft4bDyd8KVyyjoOUqBzq5NLqx4itk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=A74PjBdPW4zj0Mph7aGGoQTiCKy7aBTkYKaPkXhU9DiPxbDItjnucxCc4wTPBAw31 6WKOggkK4srMsM1op220wzimf2PiKU+bjI/+nw/wscb8ODi6EWqGhSlrSC2YJUu/gS TZVI8hIZHhJtktozqoPxcqVbsbZQ0jMwNrjTSE5TvsEDu43qhYFfNSb3zJ3HNnLQ8s GEq5dELXkQS+tWYVbpfD+YinxIfqEnQ1KTZ9aaGNCDnVk0wCZMtLU3RX7akTc2DlAS gSXpMFwgJcb2NzMDoki6Kwknqac/0q1hmigYSq63YHNhQ8RK7SivqG7+vSS4kX+0Eg ZXb7DQ2En0crA== Message-ID: <603ef1ec-bccc-4fe4-9523-e8b8a731be63@kernel.org> Date: Tue, 28 Jul 2026 14:58:39 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] mm/huge_memory: add folio_split_driver_managed() To: Zi Yan Cc: Matthew Brost , intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Christian Koenig , Huang Rui , Matthew Auld , Andrew Morton , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Tvrtko Ursulin , Dave Airlie , Matthew Wilcox References: <20260722044220.1110278-1-matthew.brost@intel.com> <2FD2B991-09B3-40EE-8230-49BE3A239EEC@nvidia.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <2FD2B991-09B3-40EE-8230-49BE3A239EEC@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: intel-xe@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel Xe graphics driver List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-xe-bounces@lists.freedesktop.org Sender: "Intel-xe" On 7/27/26 20:23, Zi Yan wrote: > On 27 Jul 2026, at 13:33, David Hildenbrand (Arm) wrote: > >> On 7/22/26 17:28, Zi Yan wrote: >>> >>> Strickly speaking, these vm_insert*() compound pages are not folios, >>> since folios are supposed to be rmappable and they are either anonymous >>> memory or file-backed memory. I am working on separating them from >>> rmappable folios by replacing PG_private with PG_folio and marking all >>> pages in a folio with PG_folio in page_rmappable_folio(). >>> >>> Hopefully, we can find a better name, like refcounted_folio, later for >>> these non-rmappable compound pages. >> >> They wouldn't really be folios, I guess. They would likely be a simple >> "refcounted" memtype that allows for compound pages. > > Yes, they are not folios. But “folio” was started to replace “compound page” > and slowly becomes rmappable anon and file-backed. People outside MM still > thinks “folio” == “compound page”. Yes, it's a bit of a mess now. > But once I manage to remove PG_private > and get us PG_folio, page_folio() will return NULL for non-folio compound > pages and we will need a new type for them, “refcounted_XXX”. We can decide > XXX when I get there. :) So far willy did not document a type that just has a refcount. https://kernelnewbies.org/MatthewWilcox/Memdescs Maybe "Managed memory" (struct mgdesc) could be the right thing for some memory with a refcount. The question is, if the use case at hand would even require a refcount, of if frozen pages would be good enough. > >> >> But what is the conclusion here? It sounds like "folio_split_" is the entirely >> wrong interface for these compound pages. > > We probably would allow folio_split() to be used on compound pages now > until we can make a clean distinction, e.g., using PG_folio, between them. > > Yes, folio_split() and its helper functions are meant for rmappable anon and > file-backed folios. But currently “folio” is de facto “compound page”, since > for example prep_compound_head() initializes folio fields even if it is meant > only for compound pages. If we can stop more abuse right from the start, that would be nice. We do have split_page() that splits a non-compound higher-order page. Maybe we want a split_compound_page(), or allow for split_page() to accept compound pages. Because splitting a folio is really something different than splitting just some compound page (no mapping/pagecache/whatever involved). -- Cheers, David