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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-441d43d6ee7sm29247575e9.20.2025.05.07.05.06.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 May 2025 05:06:36 -0700 (PDT) Date: Wed, 7 May 2025 13:06:29 +0100 From: David Laight To: Matthew Wilcox Cc: WangYuli , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, yuzhao@google.com, stevensd@chromium.org, kaleshsingh@google.com, zhanjun@uniontech.com, niecheng1@uniontech.com, guanwentao@uniontech.com Subject: Re: [PATCH] mm: vmscan: Avoid signedness error for GCC 5.4 Message-ID: <20250507130629.303b01f8@pumpkin> In-Reply-To: References: <85050791B887DC13+20250506160238.799984-1-wangyuli@uniontech.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 1773D8000B X-Stat-Signature: hf1msb68ghx5xsrwx5pa81p57n5qurt7 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1746619598-961699 X-HE-Meta: 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 T4tWeQoi yHQXr/mYHOEGruPZ7c5ye0/PcKz6+VnN4OWHeAhGW4qfiyRDoUXc2Eojcyxs2kh0v8FG7iuTwxAU9aodztsiILNyz8ZPC3U70qmFW3i9WS0BhiVoK/lbn4A4/a/0aU9v+qqgq9Ne2Hvbu6uoIcyI9Xu0LW9bELvxscRj6iqDbqX3Lip7+NHsBvDxaKqIHM01OwRGAY5iopNAIG+ZCYuw9CAXE13hCXXTfxETL+OuCajKKFPInKSZi3x+szYJJQJDOBYyNg6DTV3Cfto5pdZAeBOzkREhlROzaKby5Es+kCeoWBw4INMX5Gj7QVNfRTzx1oZpZumgsge2qLt9+kkWI4BK5xrRl4fjE3Dk/yDU9gBuY0cW1hGryk8BjdLvvUdW1P0sjWcBkEtZqlZVbILUGBnMdYdngqoCuCX0M3+RND1Tq3ZBqCDgKaIoBouajZ4cDWOdMoEHjk7YBRsIZg7LGjVqKuD2uYC0XouBS 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, 6 May 2025 17:22:51 +0100 Matthew Wilcox wrote: > On Wed, May 07, 2025 at 12:02:38AM +0800, WangYuli wrote: > > To the compiler, (MAX_NR_TIERS - 1) (i.e., (4U - 1)) is unsigned, > > whereas tier is a signed integer. > > > > GCC 5.4 does not permit the minimum operation on such > > type-inconsistent operands. > > 1. This has nothing to do with the compiler version; the type-checking > is built into min(). > 2. We have min_t for a reason Mostly historical - to match the original inline function min(). min_t() is definitely overused, it should be the 'last resort' for a type mismatch, not the first. > 3. Why is a signed min the right answer instead of an unsigned min? > I don't seem to have the patch itself, but I' guessing it is for: for (i = tier % MAX_NR_TIERS; i <= min(tier, MAX_NR_TIERS - 1); i++) { which seems to have been added for 6.14-rc1 - so why is it only an issue now. Looks closer, I bet the function is usually inlined. David