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Subject: Re: [PATCH v2 1/2] mm/hugetlb_cgroup: move per-node usage on cross
 node migration
From: Muchun Song <muchun.song@linux.dev>
In-Reply-To: <20260918-for-hugetlb-charge-v2-1-2b6d8c2bdc36@kylinos.cn>
Date: Fri, 18 Sep 2026 11:13:57 +0800
Cc: Oscar Salvador <osalvador@suse.de>,
 David Hildenbrand <david@kernel.org>,
 Andrew Morton <akpm@linux-foundation.org>,
 Kees Cook <kees@kernel.org>,
 Colin Ian King <colin.i.king@gmail.com>,
 Shakeel Butt <shakeel.butt@linux.dev>,
 Mina Almasry <almasrymina@google.com>,
 Mike Kravetz <mike.kravetz@oracle.com>,
 linux-mm@kvack.org,
 linux-kernel@vger.kernel.org,
 Hongfu Li <lihongfu@kylinos.cn>,
 stable@vger.kernel.org
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Message-Id: <6BC6926A-38D3-47B3-A676-D89DFF8E212A@linux.dev>
References: <20260918-for-hugetlb-charge-v2-0-2b6d8c2bdc36@kylinos.cn>
 <20260918-for-hugetlb-charge-v2-1-2b6d8c2bdc36@kylinos.cn>
To: Hongfu Li <hongfu.li@linux.dev>
X-Mailer: Apple Mail (2.3864.700.51.1.1)



> On Sep 18, 2026, at 10:56, Hongfu Li <hongfu.li@linux.dev> wrote:
> 
> From: Hongfu Li <lihongfu@kylinos.cn>
> 
> hugetlb.<size>.numa_stat uses folio_nid() to account usage in
> __hugetlb_cgroup_commit_charge() and __hugetlb_cgroup_uncharge_folio().
> hugetlb_cgroup_migrate() only moves hugetlb_cgroup pointers, leaving
> per-node usage behind on the source node during cross-node migration.
> 
> When the migrated folio gets uncharged, we subtract usage from the
> destination node counter. This creates stale usage on the source node
> and unsigned long counter underflow on the destination node.
> The hugetlb.<size>.numa_stat interface exposes these incorrect per-node
> usage values to userspace.
> 
> Add a hugetlb_cgroup_move_usage() helper which moves the usage from the
> old node to the new node, and call it from hugetlb_cgroup_migrate().
> 
> Fixes: f47761999052 ("hugetlb: add hugetlb.*.numa_stat file")
> Cc: stable@vger.kernel.org
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>

Acked-by: Muchun Song <muchun.song@linux.dev>

Thanks.