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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-485237ec557sm62390935e9.2.2026.03.07.02.48.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 07 Mar 2026 02:48:57 -0800 (PST) Date: Sat, 7 Mar 2026 10:48:55 +0000 From: David Laight To: Mike Rapoport Cc: Xie Yuanbin , akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, surenb@google.com, mhocko@suse.com, nathan@kernel.org, nick.desaulniers+lkml@gmail.com, morbo@google.com, justinstitt@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH] mm: optimize once judgment with clang Message-ID: <20260307104855.1de4fc28@pumpkin> In-Reply-To: References: <20260307065405.37473-1-qq570070308@gmail.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 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? > Note that performance is really not critical here because we are already > dealing with slow path of debug code. I suspect that unlikely(a && b) is really horrid - the compiler could easily generate x = a && b; unlikely(x). Probably enough to change to unlikely(a) && b, but if it is a slow path perhaps just remove the unlikely(). David > > > Port the modification to WARN_ON_ONCE_GFP(), VM_WARN_ON_ONCE_PAGE(), > > VM_WARN_ON_ONCE_FOLIO(), VM_WARN_ON_ONCE_MM() and VM_WARN_ON_ONCE_VMA(). > > > > Cc: Andrew Morton > > Signed-off-by: Xie Yuanbin > > --- > > include/linux/mmdebug.h | 8 ++++---- > > mm/internal.h | 3 ++- > > 2 files changed, 6 insertions(+), 5 deletions(-) > > > > diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h > > index ab60ffba08f5..a167c5aa525e 100644 > > --- a/include/linux/mmdebug.h > > +++ b/include/linux/mmdebug.h > > @@ -60,7 +60,7 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi); > > static bool __section(".data..once") __warned; \ > > int __ret_warn_once = !!(cond); \ > > \ > > - if (unlikely(__ret_warn_once && !__warned)) { \ > > + if (unlikely(__ret_warn_once) && unlikely(!__warned)) { \ > > dump_page(page, "VM_WARN_ON_ONCE_PAGE(" __stringify(cond)")");\ > > __warned = true; \ > > WARN_ON(1); \ > > @@ -80,7 +80,7 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi); > > static bool __section(".data..once") __warned; \ > > int __ret_warn_once = !!(cond); \ > > \ > > - if (unlikely(__ret_warn_once && !__warned)) { \ > > + if (unlikely(__ret_warn_once) && unlikely(!__warned)) { \ > > dump_page(&folio->page, "VM_WARN_ON_ONCE_FOLIO(" __stringify(cond)")");\ > > __warned = true; \ > > WARN_ON(1); \ > > @@ -91,7 +91,7 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi); > > static bool __section(".data..once") __warned; \ > > int __ret_warn_once = !!(cond); \ > > \ > > - if (unlikely(__ret_warn_once && !__warned)) { \ > > + if (unlikely(__ret_warn_once) && unlikely(!__warned)) { \ > > dump_mm(mm); \ > > __warned = true; \ > > WARN_ON(1); \ > > @@ -102,7 +102,7 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi); > > static bool __section(".data..once") __warned; \ > > int __ret_warn_once = !!(cond); \ > > \ > > - if (unlikely(__ret_warn_once && !__warned)) { \ > > + if (unlikely(__ret_warn_once) && unlikely(!__warned)) { \ > > dump_vma(vma); \ > > __warned = true; \ > > WARN_ON(1); \ > > diff --git a/mm/internal.h b/mm/internal.h > > index 6e1162e13289..52367f52d623 100644 > > --- a/mm/internal.h > > +++ b/mm/internal.h > > @@ -93,7 +93,8 @@ struct pagetable_move_control { > > static bool __section(".data..once") __warned; \ > > int __ret_warn_once = !!(cond); \ > > \ > > - if (unlikely(!(gfp & __GFP_NOWARN) && __ret_warn_once && !__warned)) { \ > > + if (unlikely(__ret_warn_once) && !(gfp & __GFP_NOWARN) && \ > > + unlikely(!__warned)) { \ > > __warned = true; \ > > WARN_ON(1); \ > > } \ > > -- > > 2.51.0 > > >