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Tue, 24 Mar 2026 08:23:29 -0700 (PDT) Received: from gourry-fedora-PF4VCD3F ([2620:10d:c091:500::de62]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-89c85335745sm117576556d6.32.2026.03.24.08.23.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Mar 2026 08:23:29 -0700 (PDT) Date: Tue, 24 Mar 2026 10:23:27 -0500 From: Gregory Price To: Donet Tom Cc: Joshua Hahn , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Qi Zheng , Axel Rasmussen , Yuanchu Xie , Wei Xu , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [RFC PATCH 6/6] mm/memcontrol: Make memory.high tier-aware Message-ID: References: <20260223223830.586018-1-joshua.hahnjy@gmail.com> <20260223223830.586018-7-joshua.hahnjy@gmail.com> <90749965-ebc8-43b2-92e3-baec5f6e3de0@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <90749965-ebc8-43b2-92e3-baec5f6e3de0@linux.ibm.com> X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: ED3F41C0011 X-Stat-Signature: thm8395okxkuocwcoftcwf1g8gyctbmk X-HE-Tag: 1774365810-856940 X-HE-Meta: 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 uCvuhmUT X2boIXDNjxVpuWFo6AwDyzY7K9kCYxFFlBOAVjtkNPRitNAt6RWhSYEd0NjofXTKiRfrSFGWZX5MMyzhlIZZXjGP8+j6euaqg7FLH+rrHiMbShKTXOJHj3Fp2CXYsFt/uzdIX999JE7mKyzh15m/AeTJuW/AzYqMfccMCERxVFOiWhbOv3upi4Tmtcx5xnEVGeZT08NyhF1B8o7kwFq/W2hPVpSDZOKFPV4AAb6KcqIMv8reU5j0zoq5pHTRdfkqqITNJgEYWz7f9Zz43lBkdZaySWi+hw68R5HQujVEpGv45xuka5UORyjsmY/zv6MjsdwwruDXwbK2p3/7Oy5AXoHSKonLEGxaqAaoC6B2ZGJgoLf8Zgvg1c9rXYaEnadqLTFYqt7c9wcbkKuh1ojhtE6pDBKS+osVMA3WSnHIwe0BQJ1tUyq2Bo/DktTMfAyBlyMuf2ekUX5pFlDDIdm89npBwjQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 24, 2026 at 04:21:06PM +0530, Donet Tom wrote: > > IIUC The intent of this patch is to partition cgroup memory such that > 0 → toptier_high is backed by higher-tier memory, and > toptier_high → max is backed by lower-tier memory. > > Based on this: > > 1.If top-tier usage exceeds toptier_high, pages should be >   demoted to the lower tier. > > 2. If lower-tier usage exceeds (max - toptier_high), pages >   should be swapped out. > This is not accurate and an incorrect heuristic. Transiently, lower-tier usage may exceed (max - toptier_high) for any number of reasons which should not be used as signal for pushing swap. driving swap usage is a function of (usage > memory.high) without regard for toptier / lowtier. > 3. If total memory usage exceeds max, demotion should be >   avoided and reclaim should directly swap out pages. > This is also incorrect, as it would drive agingin inversions. Demotion is a natural extension of the LRU infrastructure: toptier active -> toptier inactive -> lowtier inactive -> swap if you do (toptier inactive -> swap) you have inverted the LRU. As far as I know, from testing, we retain all the existing behavior - we are just managing a limited resource (top tier memory) to manage the noisy-neighbor issue. So... > Should we also handle cases (2) and (3) in this patch? No, I don't think we should ~Gregory