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Fri, 16 Jan 2026 19:17:23 +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 cWpiCsOOamnQBgAAD6G6ig (envelope-from ); Fri, 16 Jan 2026 19:17:23 +0000 Message-ID: <8006ea5f-8845-436a-a2d7-125399428762@suse.cz> Date: Fri, 16 Jan 2026 20:17:22 +0100 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 , Francois Dugast Cc: 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> <20260116174947.GA1134434@nvidia.com> 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: <20260116174947.GA1134434@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: EEBAA140007 X-Rspam-User: X-Stat-Signature: k84xftytosbi3jruddeqtcdogefgp5zn X-HE-Tag: 1768591046-166116 X-HE-Meta: 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 yE9vFt6v iVAZmytmty2d6/AnQfY3hnAvqwHS3J0HFkoAsxMiUYv7XBn+guil7e9gQzKd8jqDhpYRnf7P9pZjHH09KqX6tYELpdYi0sd84HCvqswKrG3dwpoGfiPJRaXZxt0sLiSbdbmtAP4fqpxuDgvKvxj3DdwEUI5CpwURObVfpAbJdZyr3vAXTHIHNzPFeQCN9s4dTHMWXEZpiMmNSONCE4H3fz0vHH53+Xy0h23F61qlY8ZeosmFVxHPuz9Hs3zrS3/8THB/xsq+xVZRLKy66UzT1Efx1Vkykt7dzZuOXBEAzgMzOxAXwRmzmNm2ZGXpytDDMogV8guVR9rCraiw= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/16/26 18:49, Jason Gunthorpe wrote: > On Fri, Jan 16, 2026 at 12:10:16PM +0100, Francois Dugast wrote: >> -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 > > This seems too weird, why is it in the loop? There is only one > _nr_pages per folio. I suppose we could be getting say an order-9 folio that was previously used as two order-8 folios? And each of them had their _nr_pages in their head and we can't know that at this point so we have to reset everything? AFAIU this would not be a problem if the clearing of the previous state was done upon freeing, as e.g. v4 did, but I think you also argued it meant processing the pages when freeing and then again at reallocation, so it's now like this instead? Or maybe you mean that stray _nr_pages in some tail page from previous lifetimes can't affect the current lifetime in a wrong way for something looking at said page? I don't know immediately. > This is mostly zeroing some memory in the tail pages? Why? > > Why can't this use the normal helpers, like memmap_init_compound()? > > struct folio *new_folio = page > > /* First 4 tail pages are part of struct folio */ > for (i = 4; i < (1UL << order); i++) { > prep_compound_tail(..) > } > > prep_comound_head(page, order) > new_folio->_nr_pages = 0 > > ?? > > Jason