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b=e7aBuYx/zoaNFKLfyEi3UwnDYq4cH2lGtZXVK8S2AnTXEpjIkTxPvQPvbnSKGBfCE n+3ROEh/GlRyDbtHcq8cp9T2dv9o+stRSkAbb9/rXv1D02xuuuaRI3FjNcDA63olqM +f9pWQPDebd/5u3QrrvNqgVNHMvS/aGO+8a6Bnt6f5wBvuFy3QoKbraB8D/HcNnQMd uE3raa2cOTxCpXZDsVTb90cy+Wqql3A8KH42Q1xeIFfoIGLwnubw/p37bcVoUiMKf0 hbcuRernukzJBG6qSveIbRz9sujbYxISeQMTsBRVr1JQPkhXSGrVH+DWGztzhJ/Ozn umezALzzlzjwA== 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 6/7] mm/damon/core: handle extreme memory state in get_node_memcg_used_bp() Date: Tue, 1 Sep 2026 06:13:23 -0700 Message-ID: <20260901131326.97615-7-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-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: E68091C0005 X-Stat-Signature: rkia8daxb3ig98xuswmp4q6tq8crzsub X-HE-Tag: 1788268417-654760 X-HE-Meta: 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 F2p/Hj1b BglXpBMxW8zcpjinm1slFAk/nT9YhfOJvXeNb1HNrj7Fn0pVM+QaWItdS24PRdslqu4Zbax0ExlPmUQ7n0BVdgGGTBrbRmZRcIMkYGFtyjawGKNmcraHp/P6DDEgLOAZ73q64MI1H0K277z+midLiLnd+P0H/sfFrq5iUlNOADoVhfezRgGtOjPzonOe7UvtZh1YzHvQS+ZkmyCLiDLgWDW6PKqSjIumq4H40ege0rbT1blaMwkU+PA4Bx1wZ0bFJpot3YSPxvPL30bKjv64eUzAkqw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: In extreme unlikely situations, total memory might be zero. In less extreme but still very unlikely situations, lruvec_page_state() calls might let the caller show used memory larger than total memory. In the two cases, damos_get_node_memcg_used_bp() could cause division by zero, or return underflowed value, respectively. Handle the cases by respectively returning 100% and 0% for used and free memory queries in the corner cases. This issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260329154813.47382-1-sj@kernel.org Fixes: b74a120bcf50 ("mm/damon/core: implement DAMOS_QUOTA_NODE_MEMCG_USED_BP") Cc: # 6.19.x Signed-off-by: SJ Park --- mm/damon/core.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index ad3657d356fbc..3060edf5e4fa6 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2854,6 +2854,12 @@ static unsigned long damos_get_node_memcg_used_bp( mem_cgroup_put(memcg); si_meminfo_node(&i, goal->nid); + if (!i.totalram || i.totalram < used_pages) { + if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) + return 10000; + else /* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */ + return 0; + } if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) numerator = used_pages; else /* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */ -- 2.47.3