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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9DF12C54F54 for ; Tue, 28 Jul 2026 12:58:54 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 75A1E6B008C; Tue, 28 Jul 2026 08:58:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 731386B0093; Tue, 28 Jul 2026 08:58:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 623176B0095; Tue, 28 Jul 2026 08:58:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 2DBD96B008C for ; Tue, 28 Jul 2026 08:58:53 -0400 (EDT) Received: from smtpin30.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id C26EBA034C for ; Tue, 28 Jul 2026 12:58:52 +0000 (UTC) X-FDA: 85038190104.30.738CBDE Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf29.hostedemail.com (Postfix) with ESMTP id ECCA4120009 for ; Tue, 28 Jul 2026 12:58:50 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=A74PjBdP; spf=pass (imf29.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1785243531; b=CzNeJbsEXkcS4aDyBHQwvuK5g88hqWR96Dh4Gn3vMcnlhPTJ3plXLdWL2yvhJkWaiobSOg TchKTIFytoXBRfRYg3ocF5IDr+L/QRhh6S7LVcBjKxr2dipm9TlFtp8l1AkTEvrfiJq6FP VktAsNCFyCPhqslpRfXShlCDSdCV5hI= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=A74PjBdP; spf=pass (imf29.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1785243531; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Q62HDP0Erg3czKft4bDyd8KVyyjoOUqBzq5NLqx4itk=; b=E8s+JilqTN3sUdhBGfNYyAtrUsd+SpxE3ChUs0Y2yXJgDA8jxVgh7GV+N06Urqg180/blS HfrYI/2i7Hb2pd7QUdVBGHDxUWaCxwzTk8CfpK75x89E8HBueayIWUR1UxusNQv/R6serE Ab8HCusHsl9KbErbGCpxKdWI/bajglk= 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-Stat-Signature: ie5h94pegkfbcbbgk1heaypo1xkokk1r X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: ECCA4120009 X-Rspam-User: X-HE-Tag: 1785243530-37923 X-HE-Meta: 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 hYM5ls0d CJNRx0YvCfGzHrO6jkboL5OX/hZvX/FyjDgpEiImZlPoieTcytWywbpIr3N0HQyS79oLVlBtEeyCgKqBkLYu1KbOc9EgUb+0zSYpEmvpA8dLbTltsbMqqrlAkMMb/6SUzsjIGKrJd2uHt57RoCU/8gzuwAPQvDzkIySp9G6O86ZCRRiU6XcX6d8RPZiz+cBXclEH6Y0/58atsT+Srt/DHVm4Bhd49SfP9DJBeomFeflqBl3um4IKe5FrGLV/L8SADbgb0ei4mRK4jvlQLv7309fF+4yjmklkxM5iMBmrLNRJZiOHzwJmPp4otbVVRXA12yJ4Eb75bi+kse1YGPgpRtMx/VtfX4r1HVOjRAXxv2Std4vTo46FukhCdVTFM+Dqu2WvYzp0vF8qWJ1E= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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