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Howlett" , Andrew Morton , David Hildenbrand , Jonathan Corbet , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , damon@lists.linux.dev, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH 0/7] mm/damon/reclaim,lru_sort: monitor all system rams by default Date: Tue, 14 Apr 2026 18:20:28 -0700 Message-ID: <20260415012048.76508-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit DAMON_RECLAIM and DAMON_LRU_SORT set the biggest 'System RAM' resource of the system as the default monitoring target address range. The main intention behind the design is to minimize the overhead coming from monitoring of non-System RAM areas. This could result in an odd setup when there are multiple discrete System RAMs of considerable sizes. For example, there are System RAMs each having 500 GiB size. In this case, only the first 500 GiB will be set as the monitoring region by default. This is particularly common on NUMA systems. Hence the modules allow users to set the monitoring target address range using the module parameters if the default setup doesn't work for them. In other words, the current design trades ease of setup for lower overhead. However, because DAMON utilizes the sampling based access check and the adaptive regions adjustment mechanisms, the overhead from the monitoring of non-System RAM areas should be negligible in most setups. Meanwhile, the setup complexity is causing real headaches for users who need to run those modules on various types of systems. That is, the current tradeoff is not a good deal. Set the physical address range that can cover all System RAM areas of the system as the default monitoring regions for DAMON_RECLAIM and DAMON_LRU_SORT. Technically speaking, this is changing documented behavior. However, it makes no sense to believe there is a real use case that really depends on the old weird default behavior. If the old default behavior was working for them in the reasonable way, this change will only add a negligible amount of monitoring overhead. If it didn't work, the users may already be using manual monitoring regions setup, and they will not be affected by this change. Patches Sequence ================ Patch 1 introduces a new core function that will be used for the new default monitoring target region setup. Patch 2 and 3 update DAMON_RECLAIM and DAMON_LRU_SORT to use the new function instead of the old one, respectively. Patch 4 removes the old core function that was replaced by the new one, as there is no more user of it. Patch 5 updates DAMON_STAT to use the new one instead of its in-house nearly-duplicate self implementation of the functionality. Finally patches 6 and 7 update the DAMON_RECLAIM and DAMON_LRU_SORT user documentation for the new behaviors, respectively. SeongJae Park (7): mm/damon: introduce damon_set_region_system_rams_default() mm/damon/reclaim: cover all system rams mm/damon/lru_sort: cover all system rams mm/damon/core: remove damon_set_region_biggest_system_ram_default() mm/damon/stat: use damon_set_region_system_rams_default() Docs/admin-guide/mm/damon/reclaim: update for entire memory monitoring Docs/admin-guide/mm/damon/lru_sort: update for entire memory monitoring .../admin-guide/mm/damon/lru_sort.rst | 6 ++- .../admin-guide/mm/damon/reclaim.rst | 6 ++- include/linux/damon.h | 2 +- mm/damon/core.c | 49 +++++++++-------- mm/damon/lru_sort.c | 8 +-- mm/damon/reclaim.c | 14 ++--- mm/damon/stat.c | 53 ++----------------- 7 files changed, 50 insertions(+), 88 deletions(-) base-commit: 11bcd10460e9446785fc04deb5d175806a00400b -- 2.47.3