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b=jhxcEplR7ISywxsedbUTqGQu7PZiqFsRqLmJ3SUop1iqYrPGKpKqoT674IWzD2tpu vBKhSLCyTbHm0V6fYoTATWVQveKAq2w5X64m/0MQNtP+IiYN93BqNWV2ViAhcMtX1/ tqIZdRCnsYz43Xci1FCQr67kw4uCSYAx7jYvLx1WYB3dpyKaQ4+Un1lTsNMSWrmB6W dC8vgFFYVStw3iHBO6BUnogGZQuhtMB3gXe30XaprI60pLphYo6I3Ivlp4/LbIiE1+ ibEu3mqQ3WKSz2Cp3lcPTVpM5FnaQu8gT7ZIy2gGykqp8hwfyfGbLKjMaiUtZF0Czp G8fV0gNgBz3nA== From: SJ Park To: Andrew Morton Cc: SJ Park , stable@vger.kernel.org, damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 7/7] mm/damon/core: handle extreme memory state in get_in_active_mem_bp() Date: Tue, 1 Sep 2026 06:13:24 -0700 Message-ID: <20260901131326.97615-8-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260901131326.97615-1-sj@kernel.org> References: <20260901131326.97615-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: iknf5ioaqobjj43it97rtm3fp397wwy7 X-Rspamd-Queue-Id: 4578480012 X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1788268418-301222 X-HE-Meta: U2FsdGVkX1/lAJjdxoKFVnZMlNqQqTN3XQVGdgvqR6i44cga0qmHrNBmj8sXdUwQVX3uoAylyTsPMkQ3vfPhgTfV34WrPhE8R10dtuUMVfzYlb0pklp7QvaW9AQQhQR4NJGT3uUhmIdJSIb9/Fze45dI5lrMNAoIRme9P4qhOnMNbZXKtyRbomGJDJhOu0ADokcAnaQzgvHxABS0xZklLU2fBcpnY7rcv4OOTmE1+ikoWCxmfjh/z1nN2EBcpw5NBmV+MZDOSpx2q+hqY8zu0UAOEubK1H8i5L90AID0UbviscRjt3A6Cysj7e5eujAt4DoHKkHHvAbqe7/WKZQ38ecw/3dIpoiDsRLTYqPAu5QfDcuIg0nECn2jKg4jCY04Q6mzh1yeoz027tb3rZTgQB566Eyc0K7h1KtwgInvnZEEcGj2cP4GjFVheeVuswsWqi6eWhpUq9Z0deYEoQJJC/XaAwLe6wRApaolBcsb0qWXDcWYFeFjhSRG7iBKmSthhyFEkoTVhLacdCFRo+2epGfOqQGsWRQPHxpMxcANNQwg7qYMX3blPW4im09hQaPHZwyMGe3NRBNViFuOGCgaIOma1gbaZBd4bH+KcopXjlgZG4IexvLAFJiyAHZZWsv2fjhapZjYfMxfW8fUoM58GVvNYTB6WGynfWzA8IPSWL6C9q3wLclZyj9Yg7RY3qtOSfE+8tbyE9CB0NxZJfY24jYbSV48NU5ICU2Y5nkTAutaHkssSf2NPWukKSSvS32AmjOpDX53ZVCd61CH4sR2XbprqLOGUdlstl3Wc40KqFcT4+8vedT8JdEKIlUMrRgbQH+2VG643WGloQfSN8fl8aV9GXW3ct7BnxZANRLrCkjvKM2iUKiCTy3YG78kqNYcIEybfbcA3z2ecKQ4kBs+3J9yjqLnKOGC5vSaCIuumoZDbiZWs4LD/FVWzapaGQCjXlszRlERwCQNplg3lbE iJJ6X0wA kiLTK2kQfAlW7tjO8N9bOrt78RY6BvLboQ5UR2pHnKNEXCtwudLmprpu9rXk4Zm5gVnKn+7tTPB9HHA7A6MEVF7e5WYDUE+j3pmpYvoj4+MPCjOFbc7RscCV5E8iV2SMeicc6MWFytR+6760CSbNqSeMD9KchUy+YA5L0z0WFXuVO8byDxTu7JTau/44o4SdzNCbbLeCNMLHhLc5yhS6lHjPF1wj+pisasnk0Gt15YvITXENNKhIhBO0m7qyCSSDEoIMzW6H2AZRI2ZiKLiDtpr7UaQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: damos_get_in_active_mem_bp() uses the sum of the active and inactive memory amount as a denominator. In an extreme and unlikely environment, active and inactive memory might be zero. In this case, hence, it results in a divide by zero problem. Avoid it by changing the denominator to one if it is zero, before it is being used. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260721034756.147011-1-sj@kernel.org Fixes: 4835e2871321 ("mm/damon/core: introduce [in]active memory ratio damos quota goal metric") Cc: # 7.0.x Signed-off-by: SJ Park --- mm/damon/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 3060edf5e4fa6..0df785e72438f 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -3006,7 +3006,7 @@ static unsigned int damos_get_in_active_mem_bp(bool active_ratio) global_node_page_state(NR_LRU_BASE + LRU_ACTIVE_FILE); inactive = global_node_page_state(NR_LRU_BASE + LRU_INACTIVE_ANON) + global_node_page_state(NR_LRU_BASE + LRU_INACTIVE_FILE); - total = active + inactive; + total = max(active + inactive, 1); if (active_ratio) return mult_frac(active, 10000, total); return mult_frac(inactive, 10000, total); -- 2.47.3