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b=IS4NaUCZQl4owxLyOXkjofnED5AIG5ZNyQRpkBVZBoyMt8ateeyXPEa7lNhU6i4J6 OTne7u4RNdgEO8kTKPD835bdYHYEIzzIQsr5p73sCK04IEq+aDZU4YtXGL9/pCaiYr p0M+iMo+J64J/7zmfywqh5Eg8+fE6hGs9MEkbpP7sV94aXy52aO7mNVdDsIV9B8Fz7 j9fPrxqbBOFfNuY2etAIKQua52nNoNhmwemNj6VzAu0yVgptcjyIMLlSBkrD5s8WK9 TR4tehQpFQtRK9ajPeTGv+B1PNb1AcKYep11zfhv0Eh+3+1Lz4kHLDd2NQWjmQ05HJ nH3HY0AzQivCw== 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 6/8] mm/damon/core: handle extreme memory state in damon_get_node_mem_bp() Date: Mon, 31 Aug 2026 07:02:45 -0700 Message-ID: <20260831140254.72004-7-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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 9C27F1A000D X-Stat-Signature: n9ba543kqw9pyam4smke9rbffnbnau86 X-HE-Tag: 1788184985-194237 X-HE-Meta: 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 mDklKAIz sz/rZsU8qX1e7LllnGTEbF8XHDLGeqtLg7UK8Cgp8JD0s+gZord/bKz+IEHKqeMFQ1M3HDU8dr0UNqmUq0s4jFA9NVSH2e65ADA+YollV9kMfTkW8iwpKjalzSIVgHYIqvJiD5iFbkkQNDCeqBmob6RN6i61TQBnfZHtIJMXD7IoLhR/lFgoGezaiAQxggEyudQgpqn/YeZnI70LyhhY5Xfg2sUetTJcwkECWXToY4oUUfVbOV7W4wKRi6kPxpwucSgHOQH+fe89FljirqvazBCtWXw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: In an extreme and unlikely situation, si_meminfo_node() might let the caller show zero total ram. That could cause a divide by zero in damon_get_node_mem_bp(). It could also show free memory larger than the total memory. This could cause underflow and make DAMOS temporarily make unexpected behavior. Thanks to safety guards in the auto-tuning feedback loop, that should not be a real problem, though. Fix the problems by respectively returning 100% and 0% for used and free memory queries in the corner cases. The issue was discovered [1] by Sashiko. [1] https://lore.kernel.org/20260328133216.9697-1-sj@kernel.org Fixes: 0e1c773b501f ("mm/damon/core: introduce damos quota goal metrics for memory node utilization") Cc: # 6.16.x Signed-off-by: SJ Park --- mm/damon/core.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index e2900d0c984c9..75d71ac09515e 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2816,6 +2816,13 @@ static __kernel_ulong_t damos_get_node_mem_bp( } si_meminfo_node(&i, goal->nid); + if (!i.totalram || i.totalram < i.freeram) { + if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP) + return 10000; + else /* DAMOS_QUOTA_NODE_MEM_FREE_BP */ + return 0; + } + if (goal->metric == DAMOS_QUOTA_NODE_MEM_USED_BP) numerator = i.totalram - i.freeram; else /* DAMOS_QUOTA_NODE_MEM_FREE_BP */ -- 2.47.3