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b=J3meIb1RK2YZnMMG7UCvwivy9aKF/I3vkmftYzJ7hn5Mwbk7tjwH9r5FMlizxAufA Yrqdl6ZAgo5WRmHdJFE572ZlA9c/pBBJw6J9yTm5WmyGaczBcvfOefOAEhQRZ+6MNt 95+lqa4PTha8j3+MIyAUuzozy+ap4IzfoNt0ViLk= Date: Wed, 27 Aug 2025 14:48:32 -0700 From: Andrew Morton To: Max Kellermann Cc: david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: add `const` to lots of pointer parameters Message-Id: <20250827144832.87d2f1692fe61325628710f4@linux-foundation.org> In-Reply-To: <20250827192233.447920-1-max.kellermann@ionos.com> References: <20250827192233.447920-1-max.kellermann@ionos.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 52335A0004 X-Rspam-User: X-Stat-Signature: bqp5jpc7gzgwkgqz15ak73wtq635fzax X-Rspamd-Server: rspam09 X-HE-Tag: 1756331314-866104 X-HE-Meta: U2FsdGVkX1/yRBV6rAlxJ974qg2xdA/evkO6JlyEArKFJBBa+AVAW9bNAzPrZedSuVr4XLSeHzPu6a5HdjK+b4KQHsxWDXA7XBYnvez5DAV3UzJWe2SuGJeZ790YFwGToTuc6hijgq98HZOet4fo41oIBbPzd/2H5oWz9l8OsLiRDClGakdE15hXPEoiRDkpUGHSqa1O/q8GebqzaTCIkd2joH0eqknfIyjGOqC0dkAAWESdzNrYbuTRdrHvPKihN8SV/6iW2FW/WX8+257SdzGdeTtD4+E+UvzQL3fkRg+9euP+m5KbdSGCvCdVa/Bxzdvm26en/1oSPUYNEX9Nfh/n/TviDYBbB6bDPjqggy9XYSt3/koTRl3nqSICHvqwsQdBrmEqRUbD0fYbqdsLU10AZNvNY4orkLBgO+TI9CNkrwh8s8NPmvwg1Fioy79K5/eawcCPlwczxIbLv+Xn9SB3MhHe5BVKUxmDyiIv78bIgyeoJ2L0asbQcYrzogClbj+uF5tkPNhgIijawC1CkmU0+t78PNC4tKMY4ZM0c3zmWL2A3CmA05QtW2KIilqKLnhrym4yZbmfP4QRnMyqsYN+0SkB9RntNi1TSf5wP05XXJ/KVJjLDKwKIkGZYLLj8YTNrrAwJxyMQoWyN5Fj1qL9RaMhaI5ehU5f++vyXFNpw7HI6AiP2E6N4ueK+49TnC0tXbUvQr85tU5kEnS9t30jP4XkqQUq3VEMUDkGiRX01KRD70H9xOxH/XxyxxPF4tlegNCPC5GF5N5soE2Y/As5doHNHw59Dn/Y6pQVkiDUNGCcZyh4ihx2Esj0d4TAEUnT2ZtqLiLiZ9KGHoNDopRJ73/t/eJ1cyZ4EFY6/02qSU5C9xnkUkCV1notkqYysKqcoC+FrzjmIOm/hz0ubof617z1+6auGFLirBxmGZ0LHd6AGkuOJe8SGPzuUSm3ScCoTt42TDHAuOOG2de /9ZWFB/B 5znSmTyrYU8YdHT9TLzZfLcslwmfdwiMe103vQQGGVP1PvOtFMMP1e9mwbmVAtIIy0SX+NWGjHOuheDeBdqNc1CBzJ+sp5rlSize28ZnRoDGgc0bIYgHhfoafYayxWOukgajERwnGajmRxTxQ5oISssg4+ehvbw7IuzDwUV9B7fz06K2EfEtG11Smn4z4H82JKdUJK0yvXlFc8bo63LPjOHWpwavKgzrEVO/R2Iuken4K8gll9BLXS3paqnqy/7RCqUVwt3ZI41q0eR346/3a3nVvKhIHljMPyDlbnU+wRNzj6BMFDk1w3Wor2Q== 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 Wed, 27 Aug 2025 21:22:33 +0200 Max Kellermann wrote: > For improved const-correctness. OK... > > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -537,7 +537,7 @@ struct address_space { > /* > * Returns true if any of the pages in the mapping are marked with the tag. > */ > -static inline bool mapping_tagged(struct address_space *mapping, xa_mark_t tag) > +static inline bool mapping_tagged(const struct address_space *mapping, xa_mark_t tag) > { > return xa_marked(&mapping->i_pages, tag); > } I'd actually be in favor of making all incoming args const (C should have made this the default). Because modifying an incoming arg is just obnoxious. That value should be viewed as part of the calling environment and should not be altered. Try modifying a lengthy function and wanting to get at an incoming arg only to find that something in the preceding 100 lines has gone and messed with it. Or forget to check fr this and get a nasty surprise when testing. Not that I'm suggesting that someone go in and make this change. On the other hand, it would be neat if gcc had an option to warn when someone does this. I bet it would be simple to add.