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 5A94F3B9952; Sat, 1 Aug 2026 17:36:07 +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=1785605768; cv=none; b=QrxSxGFWLJ4huIgQwizozeoA2qIv7IbdPOMSFrQb1X0pKVWOee5y18KbNhaTbb+GqKrkVB9+uXeGcCxCPmbHGthkw9RJ6mvHk/Oo//59Jtq2o79A4VuTemLq0qK93Dk64J8OYr9Ok3yAZc80G2J0N5rwFPFf8mlNt0eg1cosi7Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785605768; c=relaxed/simple; bh=TsApn/EBuEZDdp22FMCoBKg8o3mNdte07+twbtXDt38=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ExPkJyaBvDsiibfbVQtuG3Whwv7okaVp9IfNbLvsp4tB+ZJZ8FhCZMjwCKy9vdpeRYA6Q4fa0Ljtjb2SW/WVLcYrBjdFSMnsv5cVdorFd1F3vOsvyI5/pFE1MZqhVwuzaFZrSg5bnpt1IaPGOrdS70bRDJu1Y4rFkPttsONkDnE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bLT4gtqM; 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="bLT4gtqM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 132801F00ADB; Sat, 1 Aug 2026 17:36:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785605767; bh=yKFkp73Zizuc7gexvqH7fNRh7GwZeAoSufeXbUk/pxY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=bLT4gtqMoalg2zLuDMjvtK/ef07qFRzpt+RM2ctRTcIZ3j9/K93AyBnxGZVuNwRng Gopobsn1Fx/WJ0+EPpcLwkzkBIyGDzjtYzBPjMV84zQg8qjWyUZm2S/h0EGdVAGM97 8+ddelOUyoG40WvlZHuHGfMa4oVq/Q7lZQjm5vDVaU6vHW1HSRoL2qKTCb8fPT2DCb 8VbgD0EaeCNFedX9ba2aXObuYY/jOAyAh0LmpwssCEGEzmr2Lr9FhrYr05xvYJFC1g QSnU8Y2im/ARKApd+jeszY1vR4bIsqgjhyWquzUzQ1/8vJpzmIjD43qOPfHm9UBe+n TGZ7L9lrbZd0A== 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 8/9] mm/damon/core: handle extreme memory state in get_node_memcg_used_bp() Date: Sat, 1 Aug 2026 10:35:51 -0700 Message-ID: <20260801173554.94710-9-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260801173554.94710-1-sj@kernel.org> References: <20260801173554.94710-1-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 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 269865eb8fbfa..76764a2056f7c 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2858,10 +2858,16 @@ 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