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 4DFD23C4562; 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=DXvQ9kcpsu0Q5jOF1/Vwk8vt7A0dhk92XrjcOhwD4R/wgobhyi5RrCFfTPscoZJiepAeu5UvfPOdrXp8pEvCEqDory7uNcX8VRfSuAAlDmnpupPKLrDW63tqNBWaYkyzBMxuXmcQ9jyF/ygntJ2qtyH59JMql3B1mxAUGoZFuY8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785688004; c=relaxed/simple; bh=WmQs425Ef+xSSAMNq/UxNBdA3EHvev2EgnxOjd6G0UE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=nHN6Qs+GaWoWiVIUmDqsgUf7+/HkucXpoelU9V5xHJSVPRcmWhEEjm6BSCRXXO+CR0NgmWEs24UjzqtcLcWyxVQfsNYcg3XrCn0go8ODdyie6Nq2XWA4Ychhp/wnxe2ZTCpJUUbiaSk8s0kc/dtRg5Yl93RNGT4Hp0b2IgCap9c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=i93KIxE6; 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="i93KIxE6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 096EC1F00A3A; Sun, 2 Aug 2026 16:26:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785688003; bh=UlahV7MXYAlqB2Rb+2/EWA2ZT0Z/bDkXZ3DtwrXgJX8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=i93KIxE6IhKofsUKUjSvoeTgC+o3fRHexLU8S91bisem0Lp1CY8/A9/xz5YySiK0Q DbxNTTvq6m2hy8D8QfWt79E95h9+vbIKCtq0dp65YKgGjRYF056e6++4Qo1uxQCrTB d5R+gLEHMfovUlT5Zh17788JeytKKcbJADVpsmuVsXtpqrcyEAmLbAFUUfPP8wMG86 VdV22kxE5i5yj+U2mmK1zZRiAQSM/YwnrWzamUK4AqKjapmqCXHb6gEhrQj2Yn114h YT3pGUA7OGqhLWE0GigIzBIlukKcgYSz8r+HAqrrXcwT3lNbzDmzopv7g175tufi4C 6fNpVrcK2xMGg== 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 8/9] mm/damon/core: handle extreme memory state in get_node_memcg_used_bp() Date: Sun, 2 Aug 2026 09:26:29 -0700 Message-ID: <20260802162631.90304-9-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 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 returning 100% and 0% for the two cases, respectively. 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 | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index e3f3ee75a3d33..67ad1f07c29a4 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2862,10 +2862,16 @@ static unsigned long damos_get_node_memcg_used_bp( mem_cgroup_put(memcg); si_meminfo_node(&i, goal->nid); - if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) + if (!i.totalram) + return 10000; + if (goal->metric == DAMOS_QUOTA_NODE_MEMCG_USED_BP) { numerator = used_pages; - else /* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */ + } else { + /* DAMOS_QUOTA_NODE_MEMCG_FREE_BP */ + if (i.totalram < used_pages) + return 0; numerator = i.totalram - used_pages; + } return mult_frac(numerator, 10000, i.totalram); } -- 2.47.3