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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , Brendan Jackman , Johannes Weiner , Zi Yan , Harry Yoo , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , Qi Zheng , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu , "Borislav Petkov (AMD)" , Randy Dunlap , Feng Tang , Dapeng Mi , Kees Cook , Marco Elver , Jakub Kicinski , Li RongQing , Eric Biggers , "Paul E. McKenney" , Nathan Chancellor , Nicolas Schier , Miguel Ojeda , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Thomas Gleixner , Douglas Anderson , Gary Guo , Christian Brauner , Pasha Tatashin , Coiby Xu , Masahiro Yamada , Frederic Weisbecker , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-rt-devel@lists.linux.dev, Marcelo Tosatti Subject: Re: [PATCH v4 3/4] swap: apply new pw_queue_on() interface Date: Mon, 13 Jul 2026 18:28:52 -0300 Message-ID: X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260713073158.CHjwei-N@linutronix.de> References: <20260519012754.240804-1-leobras.c@gmail.com> <20260519012754.240804-4-leobras.c@gmail.com> <20260520150736.HZnlFkv7@linutronix.de> <20260713073158.CHjwei-N@linutronix.de> 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-Disposition: inline Content-Transfer-Encoding: 8bit On Mon, Jul 13, 2026 at 09:31:58AM +0200, Sebastian Andrzej Siewior wrote: > On 2026-07-12 18:43:48 [-0300], Leonardo Bras wrote: > > > I thought that this improved since commit > > > ff042f4a9b050 ("mm: lru_cache_disable: replace work queue synchronization with synchronize_rcu") > > > > > > Did it get worse or was it not entirely gone? > > > > > > > I worked in this patchset majorly after that commit date, and it was still > > an issue up to last time Marcelo tested. Not sure of the impact of above > > commit, but I suppose it may have brought some improvements without fully > > fixing it. > > It would be good to know what is still missing and maybe it can be > addressed without introducing this remote locking. > I get the point, but the main idea is to make this as proof of concept of the mechanism, that can use to solve the latency introduced by IPIs from per-cpu workqueues. I remember discussing all those examples with Marcelo in the past, and IIRC to solve this we would either have to use per-cpu spinlocks, which is undesired in terms of performance on !RT, or skip remote operations in isolated cpus, which may have weird behaviors, or disable caches in isolated cpus which is terrible for performance there. In any case, the main goal is to get something generic enough to deal with most cases, not an individual solution. Thanks! Leo