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([2601:600:947f:f020:85dc:d2b2:c5ee:e3c4]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8971cd8d1e8sm260088336d6.24.2026.02.18.14.47.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Feb 2026 14:47:54 -0800 (PST) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <1aab1afa-d23b-40c6-8e56-a6314fa728dc@redhat.com> Date: Wed, 18 Feb 2026 17:47:52 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 1/1] rwsem: Shrink rwsem by one pointer To: "Matthew Wilcox (Oracle)" Cc: Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , linux-kernel@vger.kernel.org, Linus Torvalds , Christoph Hellwig , linux-fsdevel@vger.kernel.org References: <20260217190835.1151964-1-willy@infradead.org> <20260217190835.1151964-2-willy@infradead.org> Content-Language: en-US In-Reply-To: <20260217190835.1151964-2-willy@infradead.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/17/26 2:08 PM, Matthew Wilcox (Oracle) wrote: > Instead of embedding a list_head in struct rw_semaphore, store a pointer > to the first waiter. The list of waiters remains a doubly linked list > so we can efficiently add to the tail of the list, remove from the front > (or middle) of the list. > > Some of the list manipulation becomes more complicated, but it's a > reasonable tradeoff on the slow paths to shrink some core data structures > like struct inode. If the goal is to use only one pointer for the rwsem structure, would it make sense to change list_head to hlist_head for instance? At least we have existing helpers that can be used instead of making our own coding convention here. Cheers, Longman