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Tue, 10 Nov 2026 02:37:55 +0000 X-Mizu-Trace-ID: c121729f7cdd5ffe X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=us-ascii X-Archived-By: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3901.200.71.1.16\)) Subject: Re: [PATCH v3 3/4] mm/hugetlb: fix NR_HUGETLB accounting for unused surplus folios From: Muchun Song In-Reply-To: <20261106100521.30099-4-kaitao.cheng@linux.dev> Date: Tue, 10 Nov 2026 10:37:39 +0800 Cc: Oscar Salvador , David Hildenbrand , Andrew Morton , Mike Rapoport , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , 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 Content-Transfer-Encoding: quoted-printable Message-Id: <1B03E14E-9E1D-48DF-9159-D64A12BA57BF@linux.dev> References: <20261106100521.30099-1-kaitao.cheng@linux.dev> <20261106100521.30099-4-kaitao.cheng@linux.dev> To: Kaitao Cheng X-Mailer: Apple Mail (2.3901.200.71.1.16) X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 24357C0006 X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: 1ann6gm8sob41qza93f76g8nufe1iycx X-Rspam-User: X-HE-Tag: 1794278276-706985 X-HE-Meta: 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 L6pICpdp rxr+mxL5DcfAxgcgTknVGU2Y2WFBgBV9b8/B9/y2pNgsK+hzq0kZQRO+GavXra1I1NinfUWxjcEyCW+Crpi86k3vdmi6rVa5S2Q/UkezhpX7+E1quBH/MN6PtY1rQObptcNIsqY49odZ3P2/y/Nlv8fU7BKHd3omrnBtD+sP0y257TQLLUyurmC4aPHJIePP78ES4RJWnrl3BFCwVd9G6BVUT1xV0x+CnRySFqs4PkupK3Xo1DMofL2P/mpXt8Y928o9T50B1OVOxQJLOp1fJgEJNH7XKp2ovsrsQZlKtIakdQIGa38mzDdaBb7HEGfl0gUodA/lr/nRkTriKZxMadU7qMIQySwKIlh7NAuvRBUYaS+SY8eO3YzSSQ9W+2JZ/ulkxyM6pcvszsDnOtpQndTSy2Zo7A+2f66z9hyuDe+79MGLs28OeUujQzI+EZZkac3ug 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 > On Nov 6, 2026, at 18:05, Kaitao Cheng wrote: >=20 > From: Kaitao Cheng >=20 > free_huge_folio() unconditionally decrements NR_HUGETLB, but freshly > allocated surplus folios can be freed before the counter has been > incremented. >=20 > 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. >=20 > These paths leave unmatched decrements, causing HugeTLB usage to be > underreported and potentially underflowing the counter. >=20 > Increment NR_HUGETLB before calling free_huge_folio() in both paths > to balance its unconditional decrement. >=20 > 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 Acked-by: Muchun Song (ByteDance) Thanks.