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 D57383DA7E4; Tue, 1 Sep 2026 13:19:00 +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=1788268742; cv=none; b=mbgjOxs+H+t9+DhBiATdNnIgVya+ll8LS/2v7WhO7u19206Xq7fS6dXZscVSjf2MdGmx9JE11KVwNnlfyNB3+9dEuX/owkS8C5i6tTUN+00NPEqgH5a5Sr+sWD+Pse0tnSHgbWDcZMD49t414p0vUOJs0qA/0jqvVYQUw+3/XV4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788268742; c=relaxed/simple; bh=tzAcE6SEgWB3A7dvKIyT7G341pe6G1l97zdd278rH/8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=QsciObuILD2R7XdNCqv8iTKndQGRqwOKrJeWmIJCsb+YqOsoU8zTUOrtgVcbK16mHtPa5eJOhK3oi3VP3p4MvGo2dFXqapft8HvCX8xgWFaqUiUg21yTg+v10kstra9bwUI5+tp/J3W0HJJbWQ3VDzXIbVHB4QClCcjYuHUHT54= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WvRKDNbT; 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="WvRKDNbT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8B0DB1F00ADB; Tue, 1 Sep 2026 13:19:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788268740; bh=YLJtgrH/eA5cfD1d64StUX4ou+TBBQRag4ZJY9MXlY0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=WvRKDNbT0hyEoN7m5TjTShQ5sN5bJPnuNWLT6l7VT3lCd/KVbAfzwtJkyYLnKaccq P1Jw9u0g7PmSQBwVBlbiQEs8LfnoL/0DQbMK8XTluP/mmlATssbYqxglyn6C/fYh7l rp+7LZauxItUuyiDJ4F/zDntxqOpzYlZKFlU9xINPgFA4M7tWIzkweK9pz461bhAnY 3/Wx8HiFakAB/JN3eWrXGLGf1uJiGNbN9/qPXlnfQx+MbZgFfnQ5N0f0vD3P9DNS3Q QY/JgRdyAdRo48bYa/MLnNFX/VQqTSlkN74Z86yHtOfe/uztJgo8Qnbfn64UX4i+4q MBDXcwSvH7XyQ== 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 6/8] mm/damon/core: handle extreme memory state in damon_get_node_mem_bp() Date: Tue, 1 Sep 2026 06:18:47 -0700 Message-ID: <20260901131850.98037-7-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260901131850.98037-1-sj@kernel.org> References: <20260901131850.98037-1-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 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(). It could also show free memory larger than the total memory. This could cause underflow and make DAMOS temporarily make unexpected behavior. Thanks to safety guards in the auto-tuning feedback loop, that should not be a real problem, though. Fix the problems by respectively returning 100% and 0% for used and free memory queries in the corner cases. 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 | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index a6fdb3068262d..ad3657d356fbc 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2807,6 +2807,13 @@ static __kernel_ulong_t damos_get_node_mem_bp( } si_meminfo_node(&i, goal->nid); + if (!i.totalram || i.totalram < i.freeram) { + if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP) + return 10000; + else /* DAMOS_QUOTA_NODE_MEM_FREE_BP */ + return 0; + } + if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP) numerator = i.totalram - i.freeram; else /* DAMOS_QUOTA_NODE_MEM_FREE_BP */ -- 2.47.3