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[47.55.120.4]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4eba3803e96sm98354441cf.19.2025.10.29.12.22.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Oct 2025 12:22:15 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1vEBkM-000000051hV-46Wr; Wed, 29 Oct 2025 16:22:14 -0300 Date: Wed, 29 Oct 2025 16:22:14 -0300 From: Jason Gunthorpe To: Lorenzo Stoakes Cc: Andrew Morton , Muchun Song , Oscar Salvador , David Hildenbrand , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Axel Rasmussen , Yuanchu Xie , Wei Xu , Peter Xu , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Kees Cook , Matthew Wilcox , John Hubbard , Leon Romanovsky , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Xu Xin , Chengming Zhou , Jann Horn , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Pedro Falcato , Shakeel Butt , David Rientjes , Rik van Riel , Harry Yoo , Kemeng Shi , Kairui Song , Nhat Pham , Baoquan He , Chris Li , Johannes Weiner , Qi Zheng , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 4/4] mm: introduce and use VMA flag test helpers Message-ID: <20251029192214.GT760669@ziepe.ca> References: Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Oct 29, 2025 at 05:49:38PM +0000, Lorenzo Stoakes wrote: > We introduce vma_flags_test() and vma_test() (the latter operating on a > VMA, the former on a pointer to a vma_flags_t value). > > It's useful to have both, as many functions modify a local VMA flags > variable before setting the VMA flags to this value. Hmm, sure would be nice to not have this inconsistency though. It is a bit wordy but with the C preprocessor we can make this work: struct vm_flags_t {DECLARE_BITMAP(..)}; void func(..) { struct vm_flags_t flags = OR_VMA_FLAGS(VMA_READ_BIT, VMA_WRITE_BIT); flags = vm_flags_or(flags, OR_VMA_FLAGS(VMA_MAYREAD_BIT, VMA_MAYWRITE_BIT); } Where OR_VMA_FLAGS's OR's together its __VA_ARGS__ and returns a struct vm_flags_t. Would that be interesting? Eliminate the inconsistency? eg https://stackoverflow.com/questions/77244843/c-macro-to-bitwise-or-together-a-variable-number-of-arguments-lightweight-solut Or other similar solutions. The compiler is pretty smart so this would all fold away to very few instructions. Then everything only works with _BIT and we don't have the special first word situation. Jason