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Fri, 13 Feb 2026 09:16:25 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Suren Baghdasaryan Date: Fri, 13 Feb 2026 17:16:14 +0000 X-Gm-Features: AZwV_QhbHh33PpamBb4RLF5fCzFN3MBz1GIFZu4QV5yrw682piRgoSYsRH-hgfg Message-ID: Subject: Re: [REGRESSION] mm/mprotect: 2x+ slowdown for >=400KiB regions since PTE batching (cac1db8c3aad) To: Pedro Falcato Cc: "David Hildenbrand (Arm)" , Luke Yang , dev.jain@arm.com, jhladky@redhat.com, akpm@linux-foundation.org, Liam.Howlett@oracle.com, willy@infradead.org, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 5BE4720003 X-Stat-Signature: hg8p1k97w9hbokte8ys36tpqgwqy8pjq X-Rspam-User: X-HE-Tag: 1771002987-951308 X-HE-Meta: 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 ncBwjIPE VUEg3/14rPguno+pVYeO5/XzkUCz5FpkbLbDu+fMbH26lg1K7OI5J4Qqztdy/AOjX7MQO/YG7hGMkGg5Vca71Du+L2L+5hSjDwolqEa2dg2DQxuNYnCTkqGW+1+mFdKhRp39InNaapU6Gx/OVPO2TmHEQ1eua9N6TbqvLYUj5Ju+XKaGongR1ToamJ8kCwWSwzFCeJoLztRA09vvFLMdXdFA3lvEj+BNaKhxP6DA6kjrAs28= 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 4:24=E2=80=AFPM Pedro Falcato wr= ote: > > 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). I agree. When I straced Android's zygote a while ago, mprotect() came up #30 in the list of most frequently used syscalls and one of the most used mm-related syscalls due to its use during process creation. However, I don't know how often it's used on VMAs of size >=3D400KiB. > > 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