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 79115432E60; Tue, 1 Sep 2026 13:19:01 +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=mlg6F2hQ/kuKB8g4Z+SBr0m2g//q7e+WwM1lRf+wVWVOClgbWQfprlM0WN4Ud9xbf72itW6qB5dDVkdzl6DEWVi4EnkKRyW1A24iXN0ZYLLUurcU4jUTjqfy5QFQFizdySLZpyKfN5XDWnLUK60mqvJuotdf8xz0dMmjMKz4O5c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788268742; c=relaxed/simple; bh=lZqnF/fq0s75WPlK1Ldiv9o028oS83xr/Lv60UdZAxc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=M00EoEFCcKQMBmB5n8dkQbCbWQVJpvJU6Shpj4uyX80iYgTekf9rbYSG4HX8NcGhDlEOFzkAhIHJuTKOomRMhyCYwDdHkjjKW60G7UkM5P11aZnbL/AgGCT4A1F9offB+08/8rZG6k0khbsJZCsZa9CCpNhu/hjGHFeP9kYDAc4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZwKYNYCW; 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="ZwKYNYCW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E25D21F00A3D; 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=1788268741; bh=/E3Oie88We+VUNBoQinHbEvxciAXpLnuOmC5tKc4/XE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ZwKYNYCWXkf3YcSo51XFKfIBjCb8OCl5BO+I54kmq6FiZHkliHE7g1on9UYpfxsdU 2SDIwQfVwj2Zf7vAcXQVsVbi8q3wupnNKn/brVsZzmIY3rYNCGLkn2YO7VOESECV3W 8OQIjhhtUNLHhUCyhUxO40Al8ceT8Izf16Ej6fi06DtaHFKPu/1bJFljhROx4NhcJn doJSWRCIQJbfbftYigig4hpE6Yx+vjeUpX7HJLzSd9t6OQk7xxMevPVSa1x60QFS+z c1LVdwXDuKxe0+hxv6I/2HVsHfGAYVcMaD2mfnoBkIE0SOzWAiBgO7oP+vSlj27mzZ lXe3py30Y8SAA== 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 7/8] mm/damon/core: handle extreme memory state in get_node_memcg_used_bp() Date: Tue, 1 Sep 2026 06:18:48 -0700 Message-ID: <20260901131850.98037-8-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 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 ad3657d356fbc..3060edf5e4fa6 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2854,6 +2854,12 @@ 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