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[71.191.243.150]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8a593bf4b0fsm154393106d6.15.2026.04.07.09.56.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Apr 2026 09:56:34 -0700 (PDT) Date: Tue, 7 Apr 2026 12:56:31 -0400 From: Gregory Price To: Lorenzo Stoakes Cc: Johannes Weiner , Shakeel Butt , lsf-pc@lists.linux-foundation.org, Andrew Morton , David Hildenbrand , Michal Hocko , Qi Zheng , Chen Ridong , Emil Tsalapatis , Alexei Starovoitov , Axel Rasmussen , Yuanchu Xie , Wei Xu , Kairui Song , Matthew Wilcox , Nhat Pham , Barry Song <21cnbao@gmail.com>, David Stevens , Vernon Yang , David Rientjes , Kalesh Singh , wangzicheng , "T . J . Mercier" , Baolin Wang , Suren Baghdasaryan , Meta kernel team , bpf@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [LSF/MM/BPF TOPIC] Towards Unified and Extensible Memory Reclaim (reclaim_ext) Message-ID: References: <20260325210637.3704220-1-shakeel.butt@linux.dev> <42e26dbb-0180-4408-b8a8-be0cafb75ad9@lucifer.local> <248a126c-43e7-4320-b4bb-282e0b6da9c4@lucifer.local> Precedence: bulk X-Mailing-List: bpf@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 Tue, Apr 07, 2026 at 12:36:36PM +0100, Lorenzo Stoakes wrote: > > > > And the current code structure makes it difficult to whittle down the > > differences methodically. > > > > IMO modularization is the best path forward. Giving people the ability > > to experiment with a la carte combinations of features would make it > > much easier to actually production test and prove individual ideas. > ... > > In a possibly, fantasy ideal world scenario *puffs on dream pipe*, it'd be > amazing to somehow isolate the reclaim code in such a way that we could > instrument it for testing purposes. > > E.g. if it could be invoked from userland, or UML, or _something_ and then > faked out to have a certain configuration of X NUMA nodes and Y GB of RAM > with Z processes competing with total observability of what's happening in > the algorithm that could allow for really robust controllable testing and > regression tests, as well as possibly some form of fuzzing for broken > reclaim scenarios. > > *Puts dream pipe down* *picks up the pipe* At risk of being shot - this kind of stubbing / functional testing is somewhat trivial work these days via with reasonably well designed interfaces. ( read: probably not with the current api n_n;; ). So to get there, we'd need to agree on the refactor work and interfaces that make it possible to model the scenarios outside a running kernel. If we do actually want to move the core to look like: - vmscan.c : core library - lru.c : standard lru - mglru.c : mglru Might as well consider the functional testing question as well as we decide what those interfaces look like anyway. *throws the pipe into the bikeshed* ~Gregory