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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uqytt-000000080i7-1BLX; Tue, 26 Aug 2025 19:00:09 +0000 Date: Tue, 26 Aug 2025 20:00:09 +0100 From: Matthew Wilcox To: Aristeu Rozanski Cc: linux-mm@kvack.org, David Hildenbrand , Andrew Morton , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter Subject: Re: [PATCH] mm: make folio page count functions return unsigned Message-ID: References: <20250826153721.GA23292@cathedrallabs.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250826153721.GA23292@cathedrallabs.org> X-Stat-Signature: eeud3yfjk7bwus6ffkc1hwr6sr53ideh X-Rspam-User: X-Rspamd-Queue-Id: 826FC120021 X-Rspamd-Server: rspam01 X-HE-Tag: 1756234815-823378 X-HE-Meta: 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 ZXBmPjua ZJ4gIejo5rCh34NWc6sqNwc3hF4E+hZcG7v7tCcP8qOBYiZvajscZYzlUIyRgcJYu/k9jPdfIsrIYY7OPVor0BIa70yKHEDU3kDSOvR05WZESz7kUPQJprMhylSHRaKjLmSTlO6zAVvxFSbZOHdSuel2efsvjGJ47hWK0ibxzSL34L/Q= 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 Tue, Aug 26, 2025 at 11:37:21AM -0400, Aristeu Rozanski wrote: > As raised by Andrew [1], a folio/compound page never spans a negative number > of pages. Consequently, let's use "unsigned long" instead of "long" > consistently for folio_nr_pages(), folio_large_nr_pages() and compound_nr(). > > Using "unsigned long" as return value is fine, because even > "(long)-folio_nr_pages()" will keep on working as expected. Using "unsigned > int" instead would actually break these use cases. I wish I'd written down what this broke, but it did. Sometimes we pass -folio_nr_pages() to functions. If it has an unsigned long type, things can go wrong. Please don't do this.