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[209.85.219.48]) by smtp.gmail.com with ESMTPSA id c9-20020ac81109000000b003a54a19c550sm1061673qtj.57.2023.01.06.14.07.07 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Jan 2023 14:07:07 -0800 (PST) Received: by mail-qv1-f48.google.com with SMTP id qb7so1910216qvb.5 for ; Fri, 06 Jan 2023 14:07:07 -0800 (PST) X-Received: by 2002:a05:6214:1185:b0:4c6:608c:6b2c with SMTP id t5-20020a056214118500b004c6608c6b2cmr2661817qvv.130.1673042827328; Fri, 06 Jan 2023 14:07:07 -0800 (PST) MIME-Version: 1.0 References: <10302240-51ec-0854-2c86-16752d67a9be@opteya.com> In-Reply-To: From: Linus Torvalds Date: Fri, 6 Jan 2023 14:06:51 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v14 2/7] mm: add VM_DROPPABLE for designating always lazily freeable mappings To: Matthew Wilcox Cc: "Jason A. Donenfeld" , Yann Droneaud , Andy Lutomirski , Ingo Molnar , linux-kernel@vger.kernel.org, patches@lists.linux.dev, tglx@linutronix.de, linux-crypto@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, Greg Kroah-Hartman , Adhemerval Zanella Netto , "Carlos O'Donell" , Florian Weimer , Arnd Bergmann , Jann Horn , Christian Brauner , linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 73DCFA0013 X-Stat-Signature: f1scksbzu7w6s1grut3rupt6b85z3b7t X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1673042830-812341 X-HE-Meta: U2FsdGVkX18NNMNfYyoneyYukcSWNSU6b5pDD4tEWyAm5PXjv9qGh+kOuri8nH8j9HY8fl8hHAYDRsGqAPn6NXaE6IP6RzfmcjPSbFAaFhdWieeUn6FNzWg0JfJehdEqcapMrGQzy+yuRjgu068HndLGCyL+azKt7pdaAiboWeR7D8NIVy4KEDGowqOBfOjMvWSwNHpoIgFkrZpNjV/rQ5p6o2EMaqYQyDRmeppLgDINHqnQdpm6LUEPxxGW09OG84bnnfPhXUOTPpjaqJHeJN0jOtjLfeu77HH3Q5AHc6YM2RLYQuACrxQL/kIoMmBzPSosedpeXeobCpcuJsMe4S3rfwf6Vllw6UTwwrWe44edBZ8ivhH1JTpKpA0Usycq8o1tK3QjKfrY0NT2OCzmPcmZ2nGFlI5UQVcbUqj83T9vw5ZUHfkjdzleonjD5DAB1qewHX4X7xGPrkHBLaGZWYCXKOqFO8AwDNbM8zWcnlgV8pwKXDBSZcE0tpXn1i6vRIJ2x5WPVfNUveoCCrBM5hqJhYASJ2z8ip0eycY/+z4omty/XD1OZERX0KWuNIXj/zkxCE89UquEtVTHm83GWhvYGIpPhr8BCQCi2Ju2u/+6Ok/VDUhFvTRRsqTRPXDBP+VHLn47iQuHR2bKUWjr6br2x+3EE9845c0I1tsXDL/i8uhFFBhsrP6qHFYEEr+QA2p0HEkylFo/4GZ0YveSw+Pp4Kel3t6au4W9bpjG2U0CtZ+xesBQ0niBqKew+0O7Pz4SMefqIaINCKICFEWc453dbqmvUrz9lsIc6SJV5HftOCqG3MQXZCWCB66sq1Ncxlrernx1yE4x1sOdJrLdWvg+aoJNurpxw/Yod1VVK5SuVdE74GAlkT5QyH2Cv61iAU8Y8LF+TEIesPCnkopPCk9xH7a6sXcJpiTpb6tc/88YBM/59nQ+z1w/uL63joQPrmcBSCV19GHtCFfKcxr olpsF6Mn J2VGFWCgIZ5juO6lcerkqUFwfCCww+93eDLoTYOEnUCRC4qKqW8KA0C2AyERxlGUA0aCiE49AomjKn79ZUxP39BYResr1BRDvgGj5QaaoG3BgefC3T6RrqVvSf8b9ZKAcHPrWZKzlWk/9MStfq9jcKX9S4So6y6J31c8n1g5af6AUvs5A0BWiOhIGlTaoFXTvrqKDEVOyQLLTL0zqgE+r5xfs7BW9f6bF9JFHmdJjnkSgJddDt4BGWCvqx8QnZQFyQVnGOdg5Nvdz1nBS2BNZihizJDxF0Lz83Q8lUvpKe9HAG1SzqRG98ZJxQwP5NVG4h4j72h7aN7jRnmECmJho6BDchA== 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: On Fri, Jan 6, 2023 at 1:42 PM Matthew Wilcox wrote: > > > I'd be more inclined to do: > > typedef unsigned int vm_flags_t[2]; No, that's entirely invalid. Never *ever* use arrays in C for type safety. Arrays are not type safe. They can't be assigned sanely, and they silently become pointers (which also aren't type-safe, since they end up converting silently to 'void *'). If you want to use the type system to enforce things, and you don't want to rely on sparse, you absolutely have to use a struct (or union) type. So something like typedef struct { u64 val; } vm_flags_t; would be an option. Linus