From: Matthew Wilcox <willy@infradead.org>
To: Aristeu Rozanski <aris@ruivo.org>
Cc: linux-mm@kvack.org, David Hildenbrand <david@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
Maxime Ripard <mripard@kernel.org>,
Thomas Zimmermann <tzimmermann@suse.de>,
David Airlie <airlied@gmail.com>, Simona Vetter <simona@ffwll.ch>
Subject: Re: [PATCH] mm: make folio page count functions return unsigned
Date: Tue, 26 Aug 2025 20:00:09 +0100 [thread overview]
Message-ID: <aK4EOf-EE43pi-xq@casper.infradead.org> (raw)
In-Reply-To: <20250826153721.GA23292@cathedrallabs.org>
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.
next prev parent reply other threads:[~2025-08-26 19:00 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-26 15:37 Aristeu Rozanski
2025-08-26 19:00 ` Matthew Wilcox [this message]
2025-08-26 21:45 ` David Hildenbrand
2025-08-26 22:00 ` Aristeu Rozanski
2025-08-27 1:20 ` Matthew Wilcox
2025-08-27 9:14 ` David Hildenbrand
2025-08-27 9:13 ` David Hildenbrand
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