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Sat, 07 Mar 2026 06:42:18 -0800 (PST) From: Xie Yuanbin To: rppt@kernel.org, akpm@linux-foundation.org Cc: Liam.Howlett@oracle.com, david@kernel.org, justinstitt@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, llvm@lists.linux.dev, mhocko@suse.com, morbo@google.com, nathan@kernel.org, nick.desaulniers+lkml@gmail.com, qq570070308@gmail.com, surenb@google.com, vbabka@kernel.org Subject: Re: [PATCH] mm: optimize once judgment with clang Date: Sat, 7 Mar 2026 22:41:35 +0800 Message-ID: <20260307144135.380683-1-qq570070308@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Sat, 7 Mar 2026 10:12:18 +0200, Mike Rapoport wrote: > On Sat, Mar 07, 2026 at 02:54:04PM +0800, Xie Yuanbin wrote: >> commit 242b872239f6a7deacbc ("include/linux/once_lite.h: fix judgment in >> WARN_ONCE with clang") helps optimize performance and size under the >> clang compiler, but the modification is not complete. > > How much does it actually optimize for size? Basing on commit a0ae2a256046c0c5d377 ("Add linux-next specific files for 20260306"), compiler "Debian clang version 21.1.8 (5)", arm64 default defconfig, and setting CONFIG_CC_OPTIMIZE_FOR_SIZE=y, the size result is: | | size | | -| -| | Image.gz | 14256146 | | size of ".text" section in vmlinex | 17035264 | Basing on above, revert the commit 242b872239f6a7deacbc ("include/linux/once_lite.h: fix judgment in WARN_ONCE with clang"), and build again: | | size | | -| -| | Image.gz | 14258152(+2006) | | size of ".text" section in vmlinex | 17039360(+4096) | > Note that performance is really not critical here because we are already > dealing with slow path of debug code. It seems that WARN_ON_ONCE_GFP() is not affected by in CONFIG_DEBUG_VM, and it is used in __alloc_frozen_pages_noprof(), which seems to be a hot path.