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b=LtEu4rI0c+XEIKBMRx0jCl5i0gmrucNi3fExE3MyFznY+EvjMautRUqrp0lPxavkS 9K+9gF+wD5qgkViIi2rLRLs8kWBnWcdqrVmph5m6HnnMW5lmsyPB5WN7PAVoQdYq57 2w3yvspvkW432MV8LCtBiTfKXO3kneXRxXOzQ1IHz5AP5dcjNz1Gn3FIZvqnHXXZ/r Po6gYOi0zoPPBk4XD/b96TXiACv/YBUmhiwPrm4z9HG2NRU1z1K9xoLKMetCMnq8qM JCRyGNI/sMiPan+bOPRIMBmIrDnFWpgNP+jyFUTTJVoJTy1dm96RZ4lTnMrRM66/n9 Q0cETzqLBBgpQ== Date: Fri, 2 Oct 2026 21:17:43 -1000 From: Tejun Heo To: Shakeel Butt Cc: Andrew Morton , Alexei Starovoitov , Johannes Weiner , Michal Hocko , Roman Gushchin , JP Kobryn , Muchun Song , Michal Koutny , Amery Hung , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Emil Tsalapatis , Jiri Olsa , Ihor Solodrai , John Fastabend , Jiayuan Chen , hui.zhu@linux.dev, Donet Tom , Greg Thelen , Meta kernel team , linux-mm@kvack.org, bpf@vger.kernel.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 0/4] memcg_ext: memcg policy through cgroup-attached struct_ops Message-ID: References: <20260921192559.2619635-1-shakeel.butt@linux.dev> <31a871a07fccc99e953a2d633fc51edc@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 16EF91C0003 X-Stat-Signature: e3e76xkf5zee6re7yprqe5kgegeb3jg7 X-HE-Tag: 1791011864-141088 X-HE-Meta: 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 uXb2dQKZ maVriSWlDs49e0DVaq4h2DIGnGS0TeQPT3tpri3V0PV9lBSnMX/KgO4r/P6OxtoXbcOF4Zsbqul6JnlEf3Lrx2sfVX0mOWaFHnR9Oqv9L3jVSw5jzBU2uZheTJfpYwI/5KHIAKhlO2CsjwKPRdqR+LoaJrMbThTDWSMwiHzbV7aKO3R4APQ5zsxzLIAHbrpRTER5OLCPa8vpFauOfJYxDX6R7YREw5uOF6i/XqheiT+9mmrTSx3ZuqiZTi9HX7QppZXqpW1oiqKYnbJ3GOcaCyur/ZCKeWXuK9QPhKK4meBqIprAOqfyCox1rnbRko+Gu7aS5Dg/Gw+azzaSSSS1eK+eZGA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello, On Fri, Oct 02, 2026 at 03:19:38PM -0700, Shakeel Butt wrote: > > On (3), if removing synchronous enforcement wouldn't regress anything, > > that's fine, but why was it added in the first place? > > > > I added the sync enforcement to replace a Google internal feature which, on > memcg OOM, allows node controller couple of seconds to either increase the max > limit or let the memcg die. With sync enforcement, memory.high helped in simple > benchmarks. However later testing on some realistic Google workloads, I found > out that several thousand threads are very normal of typical Google workload and > memory.high sync enforcement is not effective on applications with large amount > of threads. In addition, there were workloads which on noticing blocked threads, > keep forking more threads. At the end implementing that feature using > memory.high didn't pan out. Yeah, if there's no known active usecases, might as well start by dropping it and see whether anyone complains. > > As for flexibility, we already have a gradient of enforcement around > > memory.high. Is the need here to make the shape of that gradient > > configurable? Can you give specific examples where this is needed? > > The concrete example I have is the kswapd like async reclaimers (plural) per > memcg. Kswapd is woken up on free pages falling below low watermark and then > when free pages fall below min watermark, allocators get throttled (enter direct > reclaim). I want to apply similar concept to memcg (but with right cpu > accounting and more concurrency). I see. Yeah, ISTR talking about async reclaim for memory.high. I don't know much about mm but that makes sense to me and I'm not against allowing customization of memory.high behavior via BPF; however, most use cases can likely be served with a reasonably designed dumb interface and that likely is a better place to start. Thanks. -- tejun