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 6172D3C456F; Sun, 2 Aug 2026 16:26:43 +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=1785688004; cv=none; b=hWjIUl7SY2DQfQGmjq4zjjvHKCV2HN9SmwTXsopSlT4AfchtIgc39xtQX4GqP6fktoYSVgIBvKfW3xiWUdwWn+dwhPcLCsZOxEdXmXbqbz5SDO+svnC82rpY/6pwdJheyDj7H7hDgaWAxpVrAOPzL+EvO9rldwn0g9Xsc+btW7w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785688004; c=relaxed/simple; bh=vtkwcz9sAeGBi+04ZC3OJfIwe/7uVSh2+/Pk5/qfBCk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=YucFJe+nyv/twFCw1TLPo3QOqsNAm7fkLtUl3mlUY7L3ef5ir3I697oG+5TpF416edNkM8ioYl7mp7dUV/UeSZHzV0z9UhkM7SS+tmCxHR7V0uN2/hndCMvWgz0ykx9Yy3HD8bD+C4k1agI1YNJpPCXIChVtUoRwte7UxMqXlNY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PdOII6RH; 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="PdOII6RH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A99A21F000E9; Sun, 2 Aug 2026 16:26:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785688002; bh=WiXFs5/zG+q5AEfCdPBDZKoOPM3GsSFg0ysudbMhxYI=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=PdOII6RH9kC1nW2NlNxCkQzAaSrbwyfJm9hOsB7grL0tx9y+EU0jaKwlvWNa+mWAX dk9Kf/QASWSmsRah/mGqksuXYUah1O2NAwhqWihGdMzlqRwwXOrE4to+DYCVROjI+j YIo7I02SZJSR7pIGX152i4Zg7eF9tXwbyVR526HSZ5wmERG6lgz4hjB4vziS+2yo8i KRBRNNGdeiqYN+IMWfWzqFE/ltGTztAM6BdWa+yqWdmkCp/vIvrrsUrd/8Y3nTWaWj aMroU9gExuLwYBuneUKbcTAWg3s2L0EuIeSZhznFaGjctp8wrcTN6QeFwzBkykoDd4 HXu5Ytki+3VAg== 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 v1.1 7/9] mm/damon/core: handle extreme memory state in damon_get_node_mem_bp() Date: Sun, 2 Aug 2026 09:26:28 -0700 Message-ID: <20260802162631.90304-8-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260802162631.90304-1-sj@kernel.org> References: <20260802162631.90304-1-sj@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In an extreme and unlikely situation, si_meminfo_node() might let the caller show zero total ram. That could cause a divide by zero in damon_get_node_mem_bp(). Fix it by setting the totalram one byte in the case. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260328133216.9697-1-sj@kernel.org Fixes: 0e1c773b501f ("mm/damon/core: introduce damos quota goal metrics for memory node utilization") Cc: # 6.16.x Signed-off-by: SJ Park --- mm/damon/core.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index 3bdbf4fbf7147..e3f3ee75a3d33 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2816,10 +2816,16 @@ static __kernel_ulong_t damos_get_node_mem_bp( } si_meminfo_node(&i, goal->nid); - if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP) + if (!i.totalram) + return 10000; + if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP) { numerator = i.totalram - i.freeram; - else /* DAMOS_QUOTA_NODE_MEM_FREE_BP */ + } else { + /* DAMOS_QUOTA_NODE_MEM_FREE_BP */ + if (i.totalram < i.freeram) + return 0; numerator = i.freeram; + } return mult_frac(numerator, 10000, i.totalram); } -- 2.47.3