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[209.85.208.42]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b935aead96bsm402125366b.51.2026.03.01.13.16.17 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 01 Mar 2026 13:16:18 -0800 (PST) Received: by mail-ed1-f42.google.com with SMTP id 4fb4d7f45d1cf-65f9763e8d1so7384022a12.1 for ; Sun, 01 Mar 2026 13:16:17 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCWLjNK6P52Npe6hVDWh8OzRidAUQp+ztZu6xkuVj8Ho7tQLJIwtufF6vHR/AZqP4JG+9f8yEuEofA==@kvack.org X-Received: by 2002:a17:907:3ea4:b0:b8d:c595:828 with SMTP id a640c23a62f3a-b937638a1b7mr696704166b.14.1772399777518; Sun, 01 Mar 2026 13:16:17 -0800 (PST) MIME-Version: 1.0 References: <20260228141941.f6fec687aae9d80a161387f4@linux-foundation.org> In-Reply-To: From: Linus Torvalds Date: Sun, 1 Mar 2026 13:16:01 -0800 X-Gmail-Original-Message-ID: X-Gm-Features: AaiRm5130nQ4dJ2yvhpRtMsKd9eASFSLE84mzBSKaMmz7N0KtcGUPfWjVgBJQYA Message-ID: Subject: Re: [PATCH 0/1] mm: improve folio refcount scalability To: Pedro Falcato Cc: Andrew Morton , Gladyshev Ilya , David Hildenbrand , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Zi Yan , Harry Yoo , Matthew Wilcox , Yu Zhao , Baolin Wang , Alistair Popple , Gorbunov Ivan , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Kiryl Shutsemau , Dave Chinner Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Stat-Signature: 131gzjqbttbrroopq9chqastpaqsye6i X-Rspamd-Queue-Id: 91C671C0008 X-Rspamd-Server: rspam03 X-HE-Tag: 1772399780-237120 X-HE-Meta: U2FsdGVkX1/XhlVVm7iO7syESy9b8PcwHJD4zjfvYLax9nhSqU0sfqFs0HrhGguA/Oeh3U21OYoLmLzWw4SWrdB+r+ujno+Kq9CzLx6+nn1PNxLmYJQGRm37H1aQP7C8CgI7uI08EYNX7zijpgJh8cy+Z/v5XPYIqjIyoL73WRMGzJJS277Tj/ahtIPQfVL6/9tSRPYVu2oJily8UL2MnMopxPuRGyChpEMFcIk5Xt+qbdrxkoLUDFwAMiXUF4VgHzYWHUD7vjY6h/4W2ysINveDitkY50wj6BS9dcKfO6uBQv1K5/0Db0t57obrkZBjRxnCLFwFbqh8dID56wQFU3ttn/CyUEgN7eQsaXnWGLuvkLDqfDh1EO+lFAAsPytffcEwNk2ltvopB2UsbKKDhGNgYaCLEB6sM+ezVZIp0JE47UKZeVMUgzjnuQ7RTglA/HkoPYNmiNlpyEmUH4aUKT9mj/QMT0gprAHb9tdCwYOsIYTFgCdPhVNUCuuI4P06grUZmk6YmfVWn1fZZ2FAM2++Ibm3fFf0g1fDsTYFjLf7m4WhFUoaLNugTLQ/yxUcC71Na74tU0OfuSZmJxMEtX0F1e65/ByDRfAhBz9RcF1gWNXVMJXxjSKsLd28X+1VndzHVpW8sQZ0+lsrwjhUUSqnYkNMD6udQcbcLMPMpS5Nh7CRf979Wn56JUZvFzzRLJdMBZGE3EZK3TuSwaCPgMmf4zOoQb/1kX4p0xKYGkdd57DVaWg3JrUc/+idzDQmsWqu+iWdsIsEJ9oqFQpNs0tWBzSJGU500ou0ER1byqZItPI7pt/zd30hBZC8QZcNJ8Sak7oYK11BV1VusQfdEz6ra9YlOvMBQPb18EyvppoJaNGLgs1/1lVMG/mKwjJFx1h8cAPG1YzC39Be6wCgDck5mF91ucwdIbyXbLcXrEzdVIDHJMmLI5fQ3vF4zME6t6BZ2MCxv1DM7pg4MWP Zh8sgGYw 3wwLBLlAVxjfjobZCZQ+kfH05rNVLLJloe4N/r/hFWgbRyNJMZZ57aFnekaUOC91MdRpFuwg6/qwYIM4nTuwGE/MBr45pwjvstjYLY81rwnoggcGNDqUWxr3hK8HF47FxK3oTVTOyIXhN8W5/MMsae2xWj1nQ2ctU1RXB29cTTk+xP4rCHrVDhrHm+4mYYQcUbLg/WE675+kF8XazwhlGhgZbbOZqVlNTyd0NfwaI1VPDKzXa2GFlTsiywV1jj9I2l5aDA5It0C/m4WAMphRRKYheS1/f4uf0XbW0kldnYuYGW0Jn5IZ5Te2BYQZorQX2y2COe2xBg0QaDHHOvroT8ebu4d/XpvPicP+D27V2HijZREo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 1 Mar 2026 at 12:26, Pedro Falcato wrote: > > Here we can see that the optimistic cmpxchg still can't match the xadd/lock addl > performance in single-thread, and degrades quickly and worse than straight up > cmpxchg under load (perhaps presumably because of the cmpxchg miss). Ok, thanks for doing the numbers. I'm (obviously) a bit surprised at how badly cmpxchg does - it used to be noticeably worse than "lock add" even for the non-contention case, but I thought that had long since been fixed. Clearly that's just not the case - and I had just been overly optimistic that the "first cmpxchg failed, but second one gets the value without losing the cacheline in between" would work reliably. Ho humm. Maybe that "locked" flag is the best we can do. Linus