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Fri, 23 Oct 2026 13:00:12 +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 GRe3C1xa22oBKwAAD6G6ig (envelope-from ); Fri, 23 Oct 2026 13:00:12 +0000 Date: Fri, 23 Oct 2026 14:00:10 +0100 From: Pedro Falcato To: Luiz Capitulino Cc: "Vlastimil Babka (SUSE)" , Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Jann Horn , David Hildenbrand , Jakub Matena , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [REGRESSION] mremap() fails VMA expansion when VM_MIXEDMAP is set Message-ID: References: <20261023023106.515365-1-luizcap@redhat.com> <8c53e58c-f7d2-4e98-8d03-7ff1163c1159@kernel.org> <9544f4ce-f5d1-498b-91ed-906b37122e31@redhat.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9544f4ce-f5d1-498b-91ed-906b37122e31@redhat.com> X-Spamd-Result: default: False [-13.30 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[10]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[kernel.org,linux-foundation.org,infradead.org,google.com,gmail.com,kvack.org,vger.kernel.org]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -13.30 X-Spam-Level: X-Spam-Flag: NO On Fri, Oct 23, 2026 at 08:13:56AM -0400, Luiz Capitulino wrote: > > > On 10/23/26 3:16 AM, Vlastimil Babka (SUSE) wrote: > > On 10/23/26 04:31, Luiz Capitulino wrote: > > > Growing a VM_MIXEDMAP VMA with mremap(), with or without MREMAP_MAYMOVE, fails > > > with -ENOMEM when the address range after the VMA is free. > > > > > > This regression was introduced in v6.1 by commit ca3d76b0aa80 ("mm: add merging > > > after mremap resize"). This commit changed mremap() to use vma_merge() instead > > > of vma_adjust() for the expansion case. However, vma_merge() returns NULL for > > > a VMA that has any of the VM_SPECIAL flags set. > > > > Hi, > > > > 6.1 was a rather long time ago. How was it discovered just now? I.e. what > > use case broke by the change and prompted creating the reproducer? > > The use-case that broke was an application running on an older kernel > and accessing a GPFS volume/FS. I was told that GPFS sets VM_MIXEDMAP on So the application is growing a file VMA with mremap? > a VMA because it inserts pages in the process address space with > vm_insert_page(). I then asked an LLM to check if there was anything in FWIW this is really odd for a filesystem to do. I see we have two filesystems upstream (at least in 7.3) that do this; that is, cramfs and FUSE DAX. This is arguably weird and should be fixed. Perhaps the VM side isn't giving filesystems the right flag here. -- Pedro