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Fri, 06 Nov 2026 10:06:13 +0000 X-Mizu-Trace-ID: 9dea5587c19e644f X-Migadu-Flow: FLOW_OUT From: Kaitao Cheng To: Muchun Song , Oscar Salvador , David Hildenbrand , Andrew Morton , Mike Rapoport , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt Cc: Mani Tofigh , Zi Yan , Mike Kravetz , Baolin Wang , Miaohe Lin , Naoya Horiguchi , Frank van der Linden , Chris Down , Joshua Hahn , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Kaitao Cheng Subject: [PATCH v3 3/4] mm/hugetlb: fix NR_HUGETLB accounting for unused surplus folios Date: Fri, 6 Nov 2026 18:05:20 +0800 Message-ID: <20261106100521.30099-4-kaitao.cheng@linux.dev> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20261106100521.30099-1-kaitao.cheng@linux.dev> References: <20261106100521.30099-1-kaitao.cheng@linux.dev> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 25124100007 X-Stat-Signature: p9cqmamj3a9irm8bk6abr4nxhripyrbo X-Rspam-User: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793959577-898369 X-HE-Meta: U2FsdGVkX18qDWXs3kltZKjTIUFX3T/bmsh8vKyQ/op6LghqYY+hnnkLBaw2RJgI36UUSC7tMMJG1Z2K0memQS9LJCVa8UF6AT7ywwPRaW4qnEuwJu1S1FcbHSVKIZWoDaJDXCywJZYcH7zHoivc/aeuF9nfSUJYv9bI13V0tDoYSbQ4omEjH+z8FRWUq0GlsKn5fQk/gHCH9Z2PBVNPsnzHiPc+ek8d5M4HABpYXuVup9UGfYf0yNZbhkrI/padD/GNm+bYQgDO1+VVi3kfe4vvHYizWgb1lqEs1fR9X0/9S3kPzXB+T7BrExEcc69z/AEL/NpdAiLRTl5znAKlQ2pezI4nlM9KMDyUGTJOtxny2V0V0AuoFRiO2U/ZtvlHzuhji6I3JcIN7Zk9YROkmtXssA4Cd9UG2HJaht08C9yOZtb7rtfiWMqwg1WrF9uH3nkhEFxNQiDfKzpllKZstQ7+MGZPgqaI+Jx7UHq/Tc2nwM3pW+/DcTk7GVLehFicZNrktqlDcvzl8Rg8ftEXhSNKT8tShjpTm4kxSJAqgivaQJHhENfNVoG9S9xb3YnBubrGU5rZSxQFJEKLNDX5pXKTer5vHZ3qps8CFLY7nk655Xu6m7GAZxvZMrNYgQHRzHC7nI0aLvo9tWeyib3XcHBIcSiIczDUaaoG91m1eV6Mz10HmHZkqUdHvjTnEz1cSQ1WUBoYWzuuwDT9BNoN4oXQMKqXV63JlguVE3FKhWHZahN1Zp3Db9DLeb8UryeflhsH9OZaWDqrITD4S/ZBRxBg9gZt3CT8EMe+KlS6tzOQ7t2ANeHAkb35AKSE0IWYGOHoXiyOT5/MVCKKCkOAphispUiOVoRAIIdIaShXT5ennTxlFVPRj2KnxdCjn/ZmxmQ3P7kHcfYhgaU9Hy2S0H/PbTsGJKMOY28Wg7eFiZNxtxJOrbE/WpBBnHNuGDv/xvlGY483KRiYqDI9JAa IN7aeQDB VzAV0JJkeyiu5MQK3Usk9cVSoBmh5N6HFZRaX2QaGJlRz21qZ/DVFWNmE7z+TCW2wzpRDcLc4Da9rcWXKgCx0UcxlSy8e2LljfV1e3QncsFI4TZbVNEbDXEA9ZGv0lOvYG6XYzOnsOg/dktSbZda4WmHhC5GDNCgoQPEEpW8088EV6evZFxB8Dt3YX8apq7x0MJTfOnhOCS+Kv4RjyJiJZFOqp6xY5AwgoAEagcTryj5PXuJ0+iKkTo0UZbKzUBq9qvePQXryEYheVO+RXlvoCQdWLx9J/KWQRyfkgcd2vpjvBfVcctD6XpXfg5ovZmCk3iOMc8Hiw1e87v3r+pRvtsjm7PWzXxf6+bWHhqp4tOETk6RLCQz3aVMmC7FE6MhN+7GmJzuer4gFjjTx4rxzRiLY4JjcTe3q3U+Z Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 From: Kaitao Cheng free_huge_folio() unconditionally decrements NR_HUGETLB, but freshly allocated surplus folios can be freed before the counter has been incremented. This happens when alloc_surplus_hugetlb_folio() rejects a fresh folio after its second surplus limit check. It also happens when gather_surplus_pages() frees folios because a reservation cannot be satisfied, or because concurrent pool changes leave excess folios after the reservation succeeds. These paths leave unmatched decrements, causing HugeTLB usage to be underreported and potentially underflowing the counter. Increment NR_HUGETLB before calling free_huge_folio() in both paths to balance its unconditional decrement. Fixes: 05d4532b60e3 ("memcg/hugetlb: add hugeTLB counters to memcg") Closes: https://sashiko.dev/#/bug/linux-860a3b8f-0b07-4cd5-a122-aa2288463bee Signed-off-by: Kaitao Cheng --- mm/hugetlb.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 5b5353ff5ee2..31a92ed4165a 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2140,6 +2140,8 @@ static struct folio *alloc_surplus_hugetlb_folio(struct hstate *h, if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) { folio_set_hugetlb_temporary(folio); spin_unlock_irq(&hugetlb_lock); + /* Balance the NR_HUGETLB decrement in free_huge_folio(). */ + lruvec_stat_mod_folio(folio, NR_HUGETLB, pages_per_huge_page(h)); free_huge_folio(folio); return NULL; } @@ -2384,9 +2386,13 @@ static int gather_surplus_pages(struct hstate *h, long delta) /* * Free unnecessary surplus pages to the buddy allocator. * Pages have no ref count, call free_huge_folio directly. + * These pages were not accounted in NR_HUGETLB, so balance the + * decrement in free_huge_folio(). */ - list_for_each_entry_safe(folio, tmp, &surplus_list, lru) + list_for_each_entry_safe(folio, tmp, &surplus_list, lru) { + lruvec_stat_mod_folio(folio, NR_HUGETLB, pages_per_huge_page(h)); free_huge_folio(folio); + } spin_lock_irq(&hugetlb_lock); return ret; -- 2.53.0