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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) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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