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Mon, 02 Mar 2026 07:11:29 -0800 (PST) Received: from localhost ([2603:7000:c00:3a00:365a:60ff:fe62:ff29]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-507449add38sm109824871cf.13.2026.03.02.07.11.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Mar 2026 07:11:28 -0800 (PST) Date: Mon, 2 Mar 2026 10:11:24 -0500 From: Johannes Weiner To: Andre Ramos Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, david@kernel.org, rostedt@goodmis.org Subject: Re: [PATCH] mm: add Adaptive Memory Pressure Signaling (AMPRESS) Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: A2667C0003 X-Stat-Signature: 4sxgjtiycsko6hmj17zdwdjas333b479 X-Rspam-User: X-HE-Tag: 1772464290-712101 X-HE-Meta: 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 1k5BJwoG 5Uhlm1+EXox5RAGTv4TJ+mRIlFyhE5qCMElW02jMj1mqQcOIC9iAv8hnfpwZIWnrH1XQ8iG7s5fgd5CGNRefh3qf8hX4emqgxr2IVQcWwxVVxIethscdOukcShr20m++YLQ7pkvB1zYDXyjObLxmfNivw48zHqRenK258veDO2+2Q4nGgBv3QOrj2HmjUTStMnfP9NslhPP05mgRoC1akd+147oyc6ASkKZkIWthg4WID7PEsOqELtQ8ZkP2NBVEh+2Hnv193l8W6U+93/KxCW2Mp1eBWBBecp/kXqg48Bs5vpjSs0LRq/FpscW2r32VK6eahMOel/bb9pNtcmkBJW05mnhy2Q5laZLwaC89ATB1T1ksaWq/KErXZjbbWKVKAg11mBWrPuwRNN3Ru0Mz5EL2EFA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 02, 2026 at 12:45:33AM -0300, Andre Ramos wrote: > Introduce /dev/ampress, a bidirectional fd-based interface for > cooperative memory reclaim between the kernel and userspace. > > Userspace processes open /dev/ampress and block on read() to receive > struct ampress_event notifications carrying a graduated urgency level > (LOW/MEDIUM/HIGH/FATAL), the NUMA node of the pressure source, and a > suggested reclaim target in KiB. After freeing memory the process > issues AMPRESS_IOC_ACK to close the feedback loop. > > The feature hooks into balance_pgdat() in mm/vmscan.c, mapping the > kswapd scan priority to urgency bands: > priority 10-12 -> LOW > priority 7-9 -> MEDIUM > priority 4-6 -> HIGH > priority 1-3 -> FATAL The scan priority is not a good proxy for pressure. We actually export reclaim efficiency-based pressure levels like this in memory cgroups v1, but they're being deprecated[1] in favor of PSI [2]. What are you trying to accomplish? [1] 340afb8027fa ("memcg: initiate deprecation of pressure_level") [2] Documentation/accounting/psi.rst