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[209.85.218.45]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b8fc766579asm78628666b.54.2026.02.14.08.33.12 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 14 Feb 2026 08:33:12 -0800 (PST) Received: by mail-ej1-f45.google.com with SMTP id a640c23a62f3a-b884ad1026cso250213166b.2 for ; Sat, 14 Feb 2026 08:33:12 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCXQ7XEfT9kcQISmlyZXHioHVk7ZPY5UtGHxnVXIPR2FoXS1qk5E7b+nll3yJeBzQ5KmAjyiXeflmw==@kvack.org X-Received: by 2002:a17:907:1ca2:b0:b8a:fcc5:62a6 with SMTP id a640c23a62f3a-b8fb477131bmr288214366b.61.1771086791765; Sat, 14 Feb 2026 08:33:11 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Sat, 14 Feb 2026 08:32:55 -0800 X-Gmail-Original-Message-ID: X-Gm-Features: AaiRm52CYyrFYJUGAg2XKhRJfejVrJvd1HdsP6DMfwUot2K5zPVK4w-ddgH79Uw Message-ID: Subject: Re: [RFC] making nested spin_trylock() work on UP? To: Matthew Wilcox Cc: Vlastimil Babka , Peter Zijlstra , Ingo Molnar , Will Deacon , Sebastian Andrzej Siewior , LKML , "linux-mm@kvack.org" , Waiman Long , Mel Gorman , Steven Rostedt Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: C961540002 X-Stat-Signature: 79secbb81e7k61bpdxgzapi4k4pqwg8j X-Rspam-User: X-HE-Tag: 1771086794-956068 X-HE-Meta: U2FsdGVkX1/5Gv/Dc/EOiTKJFD87DmY1F48iIYb0BQvqwm5DDpdcdThKkVvVGtSXfvnUHvk8q3UEnazHkxRemQRlvaNtkGpSIcNvJdcJfL28/2onAUy0UJKltzPWpFecEIlgAPRxGebZxNyZdCOo3AWW7hg3Cjt4HLvIANfTsbtoHS6RrlPt1czhiMpgxZu2S2Sp45/2263Sj9foDeMi4RVtfIzS5vFOV3QKiG5XsIJzYQ348pmzJExZc2EsrxPos8VVmK3n71lpZxad9CeRZfiOBxp57u07Ix9MUoB8voVmtawlyDo920OILA+4kkwXWiA+QkMqx6mzybsIMS6q6Vbyw42YzUL0AfsviM0pikJjAXRgryyofvzQayMMTd1yWae8Uaa8Zz4RHWGYScjDHeHrRsrkKbUcT0rXh/EDKfZzmnE0/zZFeUJqr3ibj2ePfxxlSoNzZGg4DV6xWjNkTF4SDi85fQVOdXHK6gS5c63OCXIi5QtO1ibfzV6kKqW5OIGtVah1dg3Has18yDbT7VVSQPUllPp9lbkfMavDDkgP7yj0J/xdtAXz5a3Zs58K5VHp6CNu8Vui0wjwS+WAu0TDeobrqKU9OrBKq5CERFc38V8QjKGjGkP/FCS4Qn9h0LygaDgHcOI+JcSR2TqgKvCx8fKvv4OigsfTqGEn+OPI6XW29Uc9SHJAKqyjHIom0WYQHRalPmNnNOukvIhU/OC3FxdJnoLstcUcOx4clCld56cyDhuBlQRNHEr+HrDkg3JGZ+OWSoJIkky1HoMxqIT9lfYop2Nsx+/X92dN3hBcPq5oCZMxsx/1h+mQu94xLFcK2GRlu7aL5cN6yOvNcgnFek5defbgup1OMK4yk/oSCsd5S3eWOf9VfMRWKTDMgYx2mrtWL2x0ksUekaqxuEMUerKU0nBKbln3oVoZjaLpFozSbnqP0gLCESKG2nO+BHQGJiUNbXb1JavKo3S OvVAwiG3 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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, 13 Feb 2026 at 22:29, Matthew Wilcox wrote: > > What if we use an atomic_t on UP to simulate there being a spinlock, > but only for pcp? Yes. Please just wrap this - very unusual - use case with a special wrapper that can then be entirely different for UP and SMP, and use something like the suggested "pcp_lock" that becomes a spinlock on smp, and just a tracking variable on UP. And I don't think it needs to even be marked as 'atomic_t' on UP - the value is going to be idempotent even when modified from interrupts (because it will just be modified back), so no need for any special logic, I think. The generic 'atomic_t' ops on UP disable interrupts, which is horrendous. Changing spinlocks globally on UP to be something they haven't been before does not sound like a good idea, particularly since no actual developer uses UP any more (and honestly, UP is dead outside of very low-end platforms or legacy like 68k). Linus