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Wed, 23 Sep 2026 09:55:54 +0000 X-Mizu-Trace-ID: 2fd1ec4fc6184996 X-Migadu-Flow: FLOW_OUT Message-ID: <2f01bd33-6b51-4978-a19b-cd1fd0bd013c@linux.dev> Date: Wed, 23 Sep 2026 17:55:49 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: hongfu.li@linux.dev, Hongfu Li , Chris Down , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, stable@vger.kernel.org, Oscar Salvador , David Hildenbrand , Andrew Morton , Shakeel Butt , Michal Hocko , Johannes Weiner , Joshua Hahn , Nhat Pham , Michal Hocko , Roman Gushchin Subject: Re: [PATCH v2 2/2] mm/memcg: migrate per-node hugetlb lruvec stat together with hugetlb folio To: Muchun Song References: <20260923-for-hugetlb_state3-v2-0-e8a36245bfab@kylinos.cn> <20260923-for-hugetlb_state3-v2-2-e8a36245bfab@kylinos.cn> <15ac7069-d687-4985-90bd-25bc900b4bdd@linux.dev> <1835413c-e2de-41b0-8225-161afa50676a@linux.dev> <10149B0C-4108-4DB6-84B7-A301E8158CA4@linux.dev> From: Hongfu Li In-Reply-To: <10149B0C-4108-4DB6-84B7-A301E8158CA4@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: szwjfty9phgt65z67i3ayhdghnw5kj54 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 6076720002 X-HE-Tag: 1790157355-4006 X-HE-Meta: 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 aic/EWDI jD6Ub8gDdA/ZCq0xP6Mzcyo03m62Ig0sL11ONvx5MMk6XfpLLpMSbR8ai8Qp8OgyRzpC9QprkAKJmen7V5x3vU2956Y0ArghYJLmMhUMYogh1rRyVCOwRFLRTtVSm9G2rlEAqe7VzRSWGxdTM5WCqC1L5arvfQD/r62fc2kM/jVUHOO8otx9/qOF/cE8/zk9bGNYh8iH2RLZZGoD+LS7Bysz4Uy1NSXvxCZBAH0btBTG889Z+c0yP2tNljpSH4jO/f6Q0dJyFgYDQX/6F0SUR0y79fYXoFMxze1U76047pd/l49iWa9mLONCIefmsASAFwPIR9PgUMitW/1sdgfXkailWy6yOpf542BkXtoTex3fn/qqM67fLTjKe/SjwCFKsUJAUKjmAPzKq3k07zTDtu9T1kg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/23/26 3:56 PM, Muchun Song wrote: > >> On Sep 23, 2026, at 11:40, Hongfu Li wrote: >> >> >> On 9/23/26 10:40 AM, Muchun Song wrote: >>> >>> On 2026/9/23 10:05, Hongfu Li wrote: >>>> From: Hongfu Li >>>> >>>> memory.numa_stat exposes per-node hugetlb counters from per-node lruvec >>>> stats. These stats are accounted against folio_nid(): incremented on >>>> the folio's node when handed to a user, decremented when the folio is >>>> returned to the pool. >>>> >>>> During hugetlb folio migration, mem_cgroup_migrate() moves the charge >>>> to the new folio and drops the memcg data of the old one, so the free >>>> of the old folio right after the migration skips the memcg per-node >>>> lruvec decrement. The hugetlb count stays attributed to the old node >>>> for the rest of the life of the charge, while the target folio gets no >>>> increment on the new node; its later free decrements a counter that >>>> was never incremented. >>>> >>>> Migrate the per-node lruvec accounting alongside migration. Global >>>> memcg totals remain balanced because they track resource consumption, >>>> not node placement. >>>> >>>> Fixes: 05d4532b60e3 ("memcg/hugetlb: add hugeTLB counters to memcg") >>>> Cc: stable@vger.kernel.org >>>> Signed-off-by: Hongfu Li >>>> Tested-by: Joshua Hahn >>>> Reviewed-by: Joshua Hahn >>>> Reviewed-by: Oscar Salvador >>>> --- >>>> include/linux/memcontrol.h | 8 ++++++++ >>>> mm/hugetlb.c | 25 +++++++++++++++++++++++++ >>>> mm/memcontrol.c | 5 ++--- >>>> 3 files changed, 35 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >>>> index a8358f297b65..74110a324f9e 100644 >>>> --- a/include/linux/memcontrol.h >>>> +++ b/include/linux/memcontrol.h >>>> @@ -984,6 +984,9 @@ unsigned long lruvec_page_state_monotonic(const struct lruvec *lruvec, >>>> unsigned long lruvec_page_state_local(const struct lruvec *lruvec, >>>> enum node_stat_item idx); >>>> +void mod_memcg_lruvec_state(struct lruvec *lruvec, >>>> + enum node_stat_item idx, int val); >>>> + >>>> void mem_cgroup_flush_stats(struct mem_cgroup *memcg); >>>> void mem_cgroup_flush_stats_ratelimited(struct mem_cgroup *memcg); >>>> @@ -1452,6 +1455,11 @@ static inline unsigned long lruvec_page_state_local(const struct lruvec *lruvec, >>>> return node_page_state(lruvec_pgdat(lruvec), idx); >>>> } >>>> +static inline void mod_memcg_lruvec_state(struct lruvec *lruvec, >>>> + enum node_stat_item idx, int val) >>>> +{ >>>> +} >>>> + >>>> static inline void mem_cgroup_flush_stats(struct mem_cgroup *memcg) >>>> { >>>> } >>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>>> index 519c30b338a8..76d019594b39 100644 >>>> --- a/mm/hugetlb.c >>>> +++ b/mm/hugetlb.c >>>> @@ -23,6 +23,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> #include >>>> #include >>>> #include >>>> @@ -7378,12 +7379,36 @@ void folio_putback_hugetlb(struct folio *folio) >>>> folio_put(folio); >>>> } >>>> +static void move_hugetlb_lruvec_stat(struct folio *old_folio, >>>> + struct folio *new_folio) >>>> +{ >>>> + struct mem_cgroup *memcg; >>>> + long nr_pages = folio_nr_pages(old_folio); >>>> + int old_nid = folio_nid(old_folio); >>>> + int new_nid = folio_nid(new_folio); >>>> + >>>> + if (old_nid == new_nid) >>>> + return; >>>> + >>>> + guard(rcu)(); >>>> + >>>> + memcg = folio_memcg(new_folio); >>>> + if (!memcg) >>>> + return; >>>> + >>>> + mod_memcg_lruvec_state(mem_cgroup_lruvec(memcg, NODE_DATA(old_nid)), >>>> + NR_HUGETLB, -nr_pages); >>> Why not use mod_lruvec_state? mod_memcg_lruvec_state is an internal >>> API for memcg, I don't want it to be exported. >> Thank you for the review. >> >> mod_lruvec_state() would update the node counter a second time. It calls >> mod_node_page_state() as well, and the target's node counter is already >> updated in alloc_hugetlb_folio_nodemask() (patch 1/2): >> >> lruvec_stat_mod_folio(folio, NR_HUGETLB, folio_nr_pages(folio)); >> >> For an uncharged folio lruvec_stat_mod_folio() only updates the node >> counter. The target folio is not charged to any memcg at that point; its >> charge only appears later in mem_cgroup_migrate(). So the node side is >> already covered and only the per-memcg attribution has to follow the >> charge here. > Looking at the first patch again, I do not think the > overall accounting is incorrect. My concern is where NR_HUGETLB > accounting is performed. > > The low-level allocation helpers only take a folio from the > hugetlb pool. They do not have enough context to decide how > the folio should be accounted. That decision should be left > to their callers, once the folio enters the relevant usage > lifecycle. > > hugetlb_alloc_folio() is a good example. It first obtains a > folio, then calls mem_cgroup_charge_hugetlb(), and only > afterwards calls lruvec_stat_mod_folio(). At that point, > the folio has the correct memcg and lruvec, so all relevant > counters can be updated together. > > After this series, alloc_hugetlb_folio_reserve() and > alloc_hugetlb_folio_nodemask() account NR_HUGETLB before > returning the folio. This makes them unsuitable for callers > that need to charge the folio afterwards. Before the charge, > lruvec_stat_mod_folio() can update only the node counter. > The later charge does not associate that earlier update with > the new memcg. > > If a caller accounts again after charging, the node counter is > updated twice. If it does not, the memcg and per-node lruvec > counters remain missing. The caller then needs a memcg-only > correction, creating a special accounting protocol between > the helper and its callers. > > Migration exposes the same issue. The target gets node > accounting before it inherits the source memcg. The second patch > must update the lruvec state and then cancel its node changes, > because the target allocation already updated the node counter. > This works, but makes the accounting lifecycle harder to follow. > > Would it be cleaner to keep these helpers focused on allocation > and let each caller account at the correct lifecycle point? > Normal allocation can account after a successful memcg charge. > Migration can move the complete lruvec state after it succeeds. Hi Muchun, Thanks a lot for the detailed explanation. One thing keeps the target accounting in alloc_hugetlb_folio_nodemask(): the node counter is paired with the folio's free, and a failed migration frees its target right away (put_new_folio()/folio_put() -> free_huge_folio(), which always decrements the node counter). If the target were accounted only after a successful migration, every failed migration would decrement a node counter that was never incremented. Unless there is a way to let free_huge_folio() tell that the folio comes from a failed migration, and skip the decrement for it. > An uncharged path can explicitly update only the node counter > if global accounting is still required. > > This would keep policy out of the low-level allocator and make > the accounting lifecycle easier to follow. > > Thanks. > >>> Thanks. >>> >>>> + mod_memcg_lruvec_state(mem_cgroup_lruvec(memcg, NODE_DATA(new_nid)), >>>> + NR_HUGETLB, nr_pages); >>>> +} >>>> + >>>> void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio, >>>> enum migrate_reason reason) >>>> { >>>> struct hstate *h = folio_hstate(old_folio); >>>> hugetlb_cgroup_migrate(old_folio, new_folio); >>>> + move_hugetlb_lruvec_stat(old_folio, new_folio); >>>> folio_set_owner_migrate_reason(new_folio, reason); >>>> /* >>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>>> index 88824f783571..a5335da5d425 100644 >>>> --- a/mm/memcontrol.c >>>> +++ b/mm/memcontrol.c >>>> @@ -1015,9 +1015,8 @@ static void __mod_memcg_lruvec_state(struct mem_cgroup_per_node *pn, >>>> put_cpu(); >>>> } >>>> -static void mod_memcg_lruvec_state(struct lruvec *lruvec, >>>> - enum node_stat_item idx, >>>> - int val) >>>> +void mod_memcg_lruvec_state(struct lruvec *lruvec, >>>> + enum node_stat_item idx, int val) >>>> { >>>> struct pglist_data *pgdat = lruvec_pgdat(lruvec); >>>> struct mem_cgroup_per_node *pn; >>>> >> -- >> Best regards, >> Hongfu -- Best regards, Hongfu