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 DB95B485508; Mon, 31 Aug 2026 14:03:04 +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=ByVdPLYoqojnl2c0XbBnO2L2XSl/ik1EWg3trDZq5unlay0BKqPLAVVS1yapqUZg+OeDRpuQsB7NF+15OQSUxfBdIpawYE60Tx3xCkQdh75Mh86DQ7mVqJovGpVRG4alVSAgeinJgo9i70B43dN/+oKJOLUWK8GdGDTAwhOLymY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788184986; c=relaxed/simple; bh=1/nML6wnR05rkV9jNVuuWopWlORtCjTUs8FNgIFWA4w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=X7g6CV6F13901/7YikHeZk4K05fSf0A0i25UokZbSaPXChnii2kyrGBm/TfCuANiEKHzx/x0D0BdmYTinzL39NzXRkvw7Wb5Yk6FctBJ/TiYJF7mK/N381yoDrSM/nYt8OrMdizfLyPM3IGShZ5r2cehQqhiAW9LmOsa5NSjY8Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IS4NaUCZ; 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="IS4NaUCZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 97BF51F00ADB; Mon, 31 Aug 2026 14:03:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788184984; bh=XKdCBVqYdsKdXO80RoHHV0o5QsCfADzPQf1ZzSc7B9k=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=IS4NaUCZQl4owxLyOXkjofnED5AIG5ZNyQRpkBVZBoyMt8ateeyXPEa7lNhU6i4J6 OTne7u4RNdgEO8kTKPD835bdYHYEIzzIQsr5p73sCK04IEq+aDZU4YtXGL9/pCaiYr p0M+iMo+J64J/7zmfywqh5Eg8+fE6hGs9MEkbpP7sV94aXy52aO7mNVdDsIV9B8Fz7 j9fPrxqbBOFfNuY2etAIKQua52nNoNhmwemNj6VzAu0yVgptcjyIMLlSBkrD5s8WK9 TR4tehQpFQtRK9ajPeTGv+B1PNb1AcKYep11zfhv0Eh+3+1Lz4kHLDd2NQWjmQ05HJ nH3HY0AzQivCw== 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 6/8] mm/damon/core: handle extreme memory state in damon_get_node_mem_bp() Date: Mon, 31 Aug 2026 07:02:45 -0700 Message-ID: <20260831140254.72004-7-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: 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(). 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 e2900d0c984c9..75d71ac09515e 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2816,6 +2816,13 @@ 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