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Fri, 13 Feb 2026 16:24:34 +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 SKlzMUJQj2m1FwAAD6G6ig (envelope-from ); Fri, 13 Feb 2026 16:24:34 +0000 Date: Fri, 13 Feb 2026 16:24:32 +0000 From: Pedro Falcato To: "David Hildenbrand (Arm)" Cc: Luke Yang , dev.jain@arm.com, jhladky@redhat.com, akpm@linux-foundation.org, Liam.Howlett@oracle.com, willy@infradead.org, surenb@google.com, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [REGRESSION] mm/mprotect: 2x+ slowdown for >=400KiB regions since PTE batching (cac1db8c3aad) Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Action: no action X-Rspamd-Queue-Id: D14EE20003 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: b75jogu8fb1b9u4s5y14jrqbkg6e4j8n X-HE-Tag: 1770999877-829289 X-HE-Meta: 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 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 Fri, Feb 13, 2026 at 04:47:29PM +0100, David Hildenbrand (Arm) wrote: > On 2/13/26 16:08, Luke Yang wrote: > > Hello, > > Hi! > > > > > we have bisected a significant mprotect() performance regression in > > 6.17-rc1 to: > > > > cac1db8c3aad ("mm: optimize mprotect() by PTE batching") > > > > The regression becomes clearly visible starting around 400 KiB region > > sizes and above. It is also still present in the latest 6.19 kernel. > > > > Micro-benchmark results are nice. But what is the real word impact? IOW, why > should we care? Well, mprotect is widely used in thread spawning, code JITting, and even process startup. And we don't want to pay for a feature we can't even use (on x86). In any case, I think I see the problem. Namely, that we now need to call vm_normal_folio() for every single PTE (this seems similar to the mremap problem caught in 0b5be138ce00f421bd7cc5a226061bd62c4ab850). I'll try to draft up a patch over the weekend if I can. -- Pedro