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b=erWnS5qgR382J6JC8z3nVk1ADCqsV8VhofU2Ph+h8YZCbWmv4FeaOqyakgTD3sVT6 SCDWU3vMlqX54v/PG7m1wVOXEswl6nXm00wz0VJf1/lwCiwoCY6x84Nr8suHAxrml1 HYX2AqXO5O0XBw0XgDnmhCcAsrFQG6jZCOXpgTM7chqvOzAfbTmkPZRdUFtgHqupVn KFECZgtDxf1hYRvQLoN0g0494AS6/lMMnnPUqTbS1HlN3doLwddGJzAqXf8UQr5gMo Wo5XQy6dUpXn7VLZLO5JQ+v4igVQ51FDFI8oDOcG+r5CGMMu3QBHsVi/DP4Xbz3rs4 5HnIhItzFoL/Q== From: SJ Park To: Cc: SJ Park , stable@vger.kernel.org, Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH v1.2 8/8] mm/damon/core: handle extreme memory state in get_in_active_mem_bp() Date: Mon, 31 Aug 2026 07:02:47 -0700 Message-ID: <20260831140254.72004-9-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260831140254.72004-1-sj@kernel.org> References: <20260831140254.72004-1-sj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 4C04820004 X-Stat-Signature: 9opkcpywz37gtx7xsu1t96gn936ccy47 X-HE-Tag: 1788184986-761295 X-HE-Meta: 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 eKJqKJzh efBeRNycBVRMrCrsibEu6vgrHFeKCD6QQJXnhyLXsTbKXIwjDeLpakWBAcwR3YPURAbjEPlNIHPyd9tn0ceozKsF0yURTafKr4GvToc0j8mBgvYq9Z2GuJKUrtXQV51zU1VLM6MkIotm/Igs2QwzX7BIbKuXvIZDaJ4BBgI8vbNsl5gETu5N1LTQSe9alivyVgt8pb1xpaXkRcbbuAMDBSAoVCZUt7CADcKQwVc8MVxIB0WXOfTDC/9piAEIIBkVPgaX3Goe5qvZocXwJy25QEENuRg== 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 3779a04753061..f8dddbff74a77 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -3015,7 +3015,7 @@ 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