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 44586485511; 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=fyAk4p0bq8i4VC9pxD4TM+Hejd9N8bEo+Ao2csFI0s5okWDWgULJd8Eb54W9lTFG/4mB9ww4MccU7+ewfpMb6wiO3SmqbWz+YzRSJZVtqONg5PapE0yW59Ozgp2KI0RxjLwQHu0YatMHn395Eq4aGEPOvcIWXGaX0g7regOuGRc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788184986; c=relaxed/simple; bh=axrgDohB9pRR8QC5Ey27g+zeND1mCd5WgD3HP/J4WSg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Heei2wg+1l3v8PBbxfdGEeFVsiKk7BRQPZowyUWJeQ5870n350Dkih0/McXDOMwscEsAkMNYcn+k9gSxEvArjg1sgViXwKvyD+bQ2aE5xdq5cRw/OMZNgs92v8wtDW1byezQiBeQ45+OmVYnxxqzaKAIdI4dyCRDN1ISFiphcBs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oJxpLDdV; 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="oJxpLDdV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EA3581F000E9; 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=1788184985; bh=wjxFgW2qNu2RQvNA0pBq7+cQKGiXodxnzF3g5CFurUE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=oJxpLDdVlPHJRD4OBQA0YEmwv5RdeoyTODGHJk9zi6EAtfAJONJ12tMhjaLQE1cQS K0bCOwsuKK8My/5RD8Dac+hvm0QNFuUtBB4m122d1FgrK+mIhgUwZosoipv0Vb+FDk d83/CCEP66tbJ5ezQ6GmckTsnB7MUtDz+QoTH+HJwKTBoI0SJjnQFAMf+uBGViCT10 TFjkYPQk8HRnfu2IMh8OxjHkCxn4BQSV8vhx2rvvdORWLOJP9dSfrF+KTHkEJhsxnG 2ZpC9BBom8O8JJhlIWu462KRFCinaOzmClyX0wS8idLOa9EwGr2T4TW5XeOPHQn5di DtyQk2vgwPyjg== 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 7/8] mm/damon/core: handle extreme memory state in get_node_memcg_used_bp() Date: Mon, 31 Aug 2026 07:02:46 -0700 Message-ID: <20260831140254.72004-8-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 In extreme unlikely situations, total memory might be zero. In less extreme but still very unlikely situations, lruvec_page_state() calls might let the caller show used memory larger than total memory. In the two cases, damos_get_node_memcg_used_bp() could cause division by zero, or return underflowed value, respectively. Handle the cases by respectively returning 100% and 0% for used and free memory queries in the corner cases. This issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260329154813.47382-1-sj@kernel.org Fixes: b74a120bcf50 ("mm/damon/core: implement DAMOS_QUOTA_NODE_MEMCG_USED_BP") Cc: # 6.19.x Signed-off-by: SJ Park --- mm/damon/core.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index 75d71ac09515e..3779a04753061 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2863,6 +2863,12 @@ static unsigned long damos_get_node_memcg_used_bp( mem_cgroup_put(memcg); si_meminfo_node(&i, goal->nid); + if (!i.totalram || i.totalram < used_pages) { + if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) + return 10000; + else /* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */ + return 0; + } if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) numerator = used_pages; else /* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */ -- 2.47.3