From: Muchun Song <muchun.song@linux.dev>
To: Kaitao Cheng <kaitao.cheng@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>,
David Hildenbrand <david@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Rapoport <rppt@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Shakeel Butt <shakeel.butt@linux.dev>,
Mani Tofigh <mt4022@columbia.edu>, Zi Yan <ziy@nvidia.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Naoya Horiguchi <nao.horiguchi@gmail.com>,
Frank van der Linden <fvdl@google.com>,
Chris Down <chris@chrisdown.name>,
Joshua Hahn <joshua.hahnjy@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
cgroups@vger.kernel.org, Kaitao Cheng <chengkaitao@kylinos.cn>
Subject: Re: [PATCH v3 3/4] mm/hugetlb: fix NR_HUGETLB accounting for unused surplus folios
Date: Tue, 10 Nov 2026 10:37:39 +0800 [thread overview]
Message-ID: <1B03E14E-9E1D-48DF-9159-D64A12BA57BF@linux.dev> (raw)
In-Reply-To: <20261106100521.30099-4-kaitao.cheng@linux.dev>
> On Nov 6, 2026, at 18:05, Kaitao Cheng <kaitao.cheng@linux.dev> wrote:
>
> From: Kaitao Cheng <chengkaitao@kylinos.cn>
>
> 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 <chengkaitao@kylinos.cn>
Acked-by: Muchun Song (ByteDance) <muchun.song@linux.dev>
Thanks.
next prev parent reply other threads:[~2026-11-10 2:38 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-06 10:05 [PATCH v3 0/4] Subject: [PATCH v3 0/4] mm/hugetlb: Fix CMA parsing, flags and usage accounting Kaitao Cheng
2026-11-06 10:05 ` [PATCH v3 1/4] mm/hugetlb_cma: fix incorrect hugetlb_cma_size assignment on malformed input Kaitao Cheng
2026-11-06 10:05 ` [PATCH v3 2/4] mm/hugetlb: Preserve persistent flags when returning folios to the pool Kaitao Cheng
2026-11-06 10:05 ` [PATCH v3 3/4] mm/hugetlb: fix NR_HUGETLB accounting for unused surplus folios Kaitao Cheng
2026-11-10 2:37 ` Muchun Song [this message]
2026-11-06 10:05 ` [PATCH v3 4/4] mm/hugetlb: Account NR_HUGETLB at folio state transitions Kaitao Cheng
2026-11-10 0:23 ` [PATCH v3 0/4] Subject: [PATCH v3 0/4] mm/hugetlb: Fix CMA parsing, flags and usage accounting Andrew Morton
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