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b=aH4mGr9UYO5eiH6AIYXjfCmgDRp3A7ggtu+GzfHkqbKy+0vL0gxX2TlSiTUU68lSO mZwlZNtMkKgE7gZt2SaP+89cW14wfxz5VTb7zjO3U4Qc/MZDUTTQBF4rKQUNfW8Pzz vLgqbwOYuL5pL7ApHNUav/WPPEIhafkLtcKq52vRCG6/UUXjJs4DEVZPEDwZkiLhHO QnLEE3cbrLBK76mO0kYVn73zwcIvs4ZkXYBBvuljg5cqfZHlHXs4VGEcqlLzNnMQCG 9QDmJGzlL2xsps7prrX2KVszEA31X9jT224ZwKGHyHVQMy/T94Bf9iriN3gqEz4pBA 1qPa6++O6An9w== Date: Sun, 8 Mar 2026 20:03:07 +0200 From: Mike Rapoport To: Xie Yuanbin Cc: akpm@linux-foundation.org, 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, surenb@google.com, vbabka@kernel.org Subject: Re: [PATCH] mm: optimize once judgment with clang Message-ID: References: <20260307144135.380683-1-qq570070308@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260307144135.380683-1-qq570070308@gmail.com> X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: D697D4000C X-Stat-Signature: aep9xhueptecu6go6noa1qry6ieoef5w X-HE-Tag: 1772992997-340158 X-HE-Meta: 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 Ioa237+i 0pae2QUjG1qVGa0e7QVRShAOjrtCMBzLQfAJY5kyiEiLZUXaHWhjyc7jlzBr5DD4VLwZBnSrqHXrkhR88ZUJRtRZdkqFsaUHPrbIQF91PuHznZD9EVVuBuzty+/E9Xwxg7Tet4c/EQbbZZkXGUSStTIUTmtK4V4tojCR5c7hr6TnqzFmYHCyMP/Kp2px6f9bpWZaSZWUkycAwnsp6IAuD1PKD/29lFX390gW4Ek4I9cc4mLo/L/iHck2SG7lR5UkH0CE5BJZ80PEjzda4F8lCTpm7/AtBawsQwWieHOEFhxwacZKIVxOU0I+4cMw8A8/QyUr9/4vBMc5NqiM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Mar 07, 2026 at 10:41:35PM +0800, Xie Yuanbin wrote: > 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) | It would be nice to see where the difference is with scripts/bloat-o-meter. And while commit 242b872239f6a7deacbc is a oneliner that essentially updates most of the _ONCE constructs, I'm not convinced that the churn in the patch that updates include/linux/mmdebug.h worth it. Do you have the numbers for this patch as well? > > 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. What might be useful there is to change the order of conditions so that __ret_warn_once will be evaluated first. -- Sincerely yours, Mike.