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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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: D85DC160003 X-Stat-Signature: 3zubb9xtiedddzx1he4pbmsionia6cck X-HE-Tag: 1785688003-52713 X-HE-Meta: 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 EC2+YB52 xbtichEvZPKsch8mPjAWcJe+R86dBQWGGtspJ++ubcHxav4X3HesqNlRpOxg74zeeHvHfQTQpVqJg5QvqBHOywYAlA+qsJoW2axOjue4p/cnb1gowSbrdFyw5216UoNTzvoQ8y+KgkiI5cy1r8ZpPiZVyTVYvIVHLQCWxh/MUQxKbTaDMUvjOPiZJjOOcl3PVWZyOxJeDMcv8SvJ72vbv2l0EgDaQWj7B0d//Wdpke9MEG6u0RWUJyVMvUtDmpHlikoD9wH3WfwGlxqDMm6bw0+p+IA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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