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Fri, 8 Aug 2025 13:38:07 +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 e9BZFL/9lWgMJgAAD6G6ig (envelope-from ); Fri, 08 Aug 2025 13:38:07 +0000 Message-ID: Date: Fri, 8 Aug 2025 15:38:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6.17 1/3] mm/mremap: allow multi-VMA move when filesystem uses thp_get_unmapped_area To: Lorenzo Stoakes , Andrew Morton Cc: "Liam R . Howlett" , Jann Horn , Pedro Falcato , David Hildenbrand , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <4f2542340c29c84d3d470b0c605e916b192f6c81.1754218667.git.lorenzo.stoakes@oracle.com> Content-Language: en-US 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: <4f2542340c29c84d3d470b0c605e916b192f6c81.1754218667.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 4EBFD100008 X-Stat-Signature: wr7ftu1s6sjpssa84zmfm5qan5fiqd66 X-HE-Tag: 1754660289-464570 X-HE-Meta: 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 Gcx7LzVq zD99Ho+krPm6OQH5kdEc4efzwLJ7QYmvX6SSBD0unkAvkCPipBlknyEQdK7eu+EkXLa5fuKBPYLLjnVDbla6eN7+U5b8lfYHeUnPVA93hrQo4j7EH3V0fcm7vun6MWrJ5s+/tqQB2yYNrpeA4pbpw3JcYULspy2aSDYFJlvnYieW0gjoiSxY3LjlLUIi9NS5u3iQQiiYKkJAirXFgBfZEpL6gcHYoSAr388OYAz3PDjpHOnhGUMCyblxLUfdt7Ol+WseijfvQaiCc+0F4FI1kvc4AWcuY5YDPNXlocWXOT8b98O7mtl8qxYot+MthsUCHWAFVDdi8PA8N79H8e1q1tm+JxqZ9twsQCZBK 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 8/3/25 13:11, Lorenzo Stoakes wrote: > We currently restrict multi-VMA move to avoid filesystems or drivers which > provide a custom f_op->get_unmapped_area handler unless it is known to > correctly handle MREMAP_FIXED. > > We do this so we do not get unexpected result when moving from one area to > another (for instance, if the handler would align things resulting in the > moved VMAs having different gaps than the original mapping). > > More and more filesystems are moving to using large folios, and typically > do so (in part) by setting f_op->get_unmapped_area to > thp_get_unmapped_area. > > When mremap() invokes the file system's get_unmapped MREMAP_FIXED, it does > so via get_unmapped_area(), called in vrm_set_new_addr(). In order to do > so, it converts the MREMAP_FIXED flag to a MAP_FIXED flag and passes this > to the unmapped area handler. > > The __get_unmapped_area() function (called by get_unmapped_area()) in turn > invokes the filesystem or driver's f_op->get_unmapped_area() handler. > > Therefore this is a point at which thp_get_unmapped_area() may be called > (also, this is the case for anonymous mappings where the size is huge page > aligned). > > thp_get_unmapped_area() calls thp_get_unmapped_area_vmflags() and > __thp_get_unmapped_area() in turn (falling back to > mm_get_unmapped_area_vm_flags() which is known to handle MAP_FIXED > correctly). > > The __thp_get_unmapped_area() function in turn does nothing to change the > address hint, nor the MAP_FIXED flag, only adjusting alignment > parameters. It hten calls mm_get_unmapped_area_vmflags(), and in turn > arch-specific unmapped area functions, all of which honour MAP_FIXED > correctly. > > Therefore, we can safely add thp_get_unmapped_area to the known-good > handlers. > > Signed-off-by: Lorenzo Stoakes Reviewed-by: Vlastimil Babka