From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.223.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B66992E719B for ; Fri, 16 Jan 2026 17:27:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.135.223.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768584461; cv=none; b=JoSRLDOhGn2BS2QSdifDiM2tueY53FWLiLLX7PwVTfxyAlJEgdKGcBrZOgcGytHR4tTIBvPDY0GpUXoejTNrScdksQ+ZoHIuwImt2YafJdfsh5cwUi+7XpY8qNEiV16KRcJhkvhCEO2+fqJ4llx4S8roxX5Yu7YfwT5Em8d4YwQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768584461; c=relaxed/simple; bh=7XIX9nvu3afzXizq2XOPrRIVleTTBXYT+Fptez4iCgI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=U5hQyfWtXS6Ya3LyxRO1vEDFaDNenRWG62pyFjduEZaNm8byXiLQud5q267va0YnwvvM9QkEmYVxI5iqSjnnYdAdREdt8Xc+OGQJrcZSL1lb5jfOKl/wHzjU2+Ljb1SoTTY7pDkOGuO3Ol+NaGl6tugy8v3bZ2qSPNFQt4G+T5w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz; spf=pass smtp.mailfrom=suse.cz; arc=none smtp.client-ip=195.135.223.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.cz Received: from imap1.dmz-prg2.suse.org (imap1.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 26A185BCEE; Fri, 16 Jan 2026 17:27:38 +0000 (UTC) Authentication-Results: smtp-out2.suse.de; none Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id D33633EA63; Fri, 16 Jan 2026 17:27:37 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id /QGJMAl1ammlHgAAD6G6ig (envelope-from ); Fri, 16 Jan 2026 17:27:37 +0000 Message-ID: <4e100125-ed70-4ec9-a0fa-5214bccd7cf3@suse.cz> Date: Fri, 16 Jan 2026 18:27:37 +0100 Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 1/5] mm/zone_device: Reinitialize large zone device private folios Content-Language: en-US To: Jason Gunthorpe Cc: Francois Dugast , intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Matthew Brost , Zi Yan , Alistair Popple , adhavan Srinivasan , Nicholas Piggin , Michael Ellerman , "Christophe Leroy (CS GROUP)" , Felix Kuehling , Alex Deucher , =?UTF-8?Q?Christian_K=C3=B6nig?= , David Airlie , Simona Vetter , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Lyude Paul , Danilo Krummrich , David Hildenbrand , Oscar Salvador , Andrew Morton , Leon Romanovsky , Lorenzo Stoakes , "Liam R . Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Balbir Singh , linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, nouveau@lists.freedesktop.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org References: <20260116111325.1736137-1-francois.dugast@intel.com> <20260116111325.1736137-2-francois.dugast@intel.com> <20260116172052.GC961572@ziepe.ca> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <20260116172052.GC961572@ziepe.ca> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spamd-Result: default: False [-4.00 / 50.00]; REPLY(-4.00)[] X-Spam-Flag: NO X-Spam-Score: -4.00 X-Rspamd-Queue-Id: 26A185BCEE X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Rspamd-Action: no action X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spam-Level: On 1/16/26 18:20, Jason Gunthorpe wrote: > On Fri, Jan 16, 2026 at 05:07:09PM +0100, Vlastimil Babka wrote: >> On 1/16/26 12:10, Francois Dugast wrote: >> > From: Matthew Brost >> > diff --git a/mm/memremap.c b/mm/memremap.c >> > index 63c6ab4fdf08..ac7be07e3361 100644 >> > --- a/mm/memremap.c >> > +++ b/mm/memremap.c >> > @@ -477,10 +477,43 @@ void free_zone_device_folio(struct folio *folio) >> > } >> > } >> > >> > -void zone_device_page_init(struct page *page, unsigned int order) >> > +void zone_device_page_init(struct page *page, struct dev_pagemap *pgmap, >> > + unsigned int order) >> > { >> > + struct page *new_page = page; >> > + unsigned int i; >> > + >> > VM_WARN_ON_ONCE(order > MAX_ORDER_NR_PAGES); >> > >> > + for (i = 0; i < (1UL << order); ++i, ++new_page) { >> > + struct folio *new_folio = (struct folio *)new_page; >> > + >> > + /* >> > + * new_page could have been part of previous higher order folio >> > + * which encodes the order, in page + 1, in the flags bits. We >> > + * blindly clear bits which could have set my order field here, >> > + * including page head. >> > + */ >> > + new_page->flags.f &= ~0xffUL; /* Clear possible order, page head */ >> > + >> > +#ifdef NR_PAGES_IN_LARGE_FOLIO >> > + /* >> > + * This pointer math looks odd, but new_page could have been >> > + * part of a previous higher order folio, which sets _nr_pages >> > + * in page + 1 (new_page). Therefore, we use pointer casting to >> > + * correctly locate the _nr_pages bits within new_page which >> > + * could have modified by previous higher order folio. >> > + */ >> > + ((struct folio *)(new_page - 1))->_nr_pages = 0; >> > +#endif >> > + >> > + new_folio->mapping = NULL; >> > + new_folio->pgmap = pgmap; /* Also clear compound head */ >> > + new_folio->share = 0; /* fsdax only, unused for device private */ >> > + VM_WARN_ON_FOLIO(folio_ref_count(new_folio), new_folio); >> > + VM_WARN_ON_FOLIO(!folio_is_zone_device(new_folio), new_folio); >> > + } >> > + >> > /* >> > * Drivers shouldn't be allocating pages after calling >> > * memunmap_pages(). >> >> Can't say I'm a fan of this. It probably works now (so I'm not nacking) but >> seems rather fragile. It seems likely to me somebody will try to change some >> implementation detail in the page allocator and not notice it breaks this, >> for example. I hope we can eventually get to something more robust. > > These pages shouldn't be in the buddy allocator at all? The driver > using the ZONE_DEVICE pages is responsible to provide its own > allocator. > > Did you mean something else? Yeah sorry that was imprecise. I meant the struct page/folio layout implementation details (which may or may not be related to the page allocator). > Jason >