From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8E886485CC1; Mon, 31 Aug 2026 14:03:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788184986; cv=none; b=LtjXfLrnLmXvVUDfdAYQmI/zeO7TF/Y8vgoKyUd0fDXhK/j/urFzsQb/1oM4mC4wpe5xYh9zBwhot1Wh25l1Gw+5s/y0RhZ8642aw2RLSZePyXWlTJqKb+7lwmgUnwKAXhj8wGPrDTftKrIAg8AbtwtnG7Lg+5yK+X23AcxFj+E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788184986; c=relaxed/simple; bh=lj/M1S5oaN42+56NlgGpIrZFtQOGxHB9iPCOijXVAX4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ATBn8aEFC3h0JdPx4dQYOUBACOy2THJ6AE7WMIkQfuM7KFBGkIeAgeRYKCT49WhKM07GMQPyFE70mFjx8n/UavAcwttCvvCRiO1jjesBzd3i1eYj1ppqjwRYxcMu4YYqKMp4tNh6C/lyLRUuf0HTJypyJnNGOtt/vVA02TrSfjM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=erWnS5qg; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="erWnS5qg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4B32B1F00ACA; Mon, 31 Aug 2026 14:03:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788184985; bh=W4ZULCHKs962Ql2lXNfqffyY3ieZ1mpdjWXyoNcHe50=; h=From:To:Cc:Subject:Date:In-Reply-To:References; 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> Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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