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From: Muchun Song In-Reply-To: <2ddd0c184829e65c5b3afa34e93599783e7af3d4.1759056506.git.zhengqi.arch@bytedance.com> Date: Mon, 29 Sep 2025 14:20:16 +0800 Cc: hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, david@redhat.com, lorenzo.stoakes@oracle.com, ziy@nvidia.com, harry.yoo@oracle.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Qi Zheng Content-Transfer-Encoding: quoted-printable Message-Id: <2EC0CBCD-73FD-400A-921A-EAB45B21ACB8@linux.dev> References: <2ddd0c184829e65c5b3afa34e93599783e7af3d4.1759056506.git.zhengqi.arch@bytedance.com> To: Qi Zheng X-Migadu-Flow: FLOW_OUT > On Sep 28, 2025, at 19:45, Qi Zheng wrote: >=20 > From: Qi Zheng >=20 > Similar to list_lru, the split queue is relatively independent and = does > not need to be reparented along with objcg and LRU folios (holding > objcg lock and lru lock). So let's apply the same mechanism as = list_lru > to reparent the split queue separately when memcg is offine. >=20 > This is also a preparation for reparenting LRU folios. >=20 > Signed-off-by: Qi Zheng > --- > include/linux/huge_mm.h | 4 ++++ > mm/huge_memory.c | 46 +++++++++++++++++++++++++++++++++++++++++ > mm/memcontrol.c | 1 + > 3 files changed, 51 insertions(+) >=20 > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index f327d62fc9852..0c211dcbb0ec1 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -417,6 +417,9 @@ static inline int split_huge_page(struct page = *page) > return split_huge_page_to_list_to_order(page, NULL, ret); > } > void deferred_split_folio(struct folio *folio, bool partially_mapped); > +#ifdef CONFIG_MEMCG > +void reparent_deferred_split_queue(struct mem_cgroup *memcg); > +#endif >=20 > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > unsigned long address, bool freeze); > @@ -611,6 +614,7 @@ static inline int try_folio_split(struct folio = *folio, struct page *page, > } >=20 > static inline void deferred_split_folio(struct folio *folio, bool = partially_mapped) {} > +static inline void reparent_deferred_split_queue(struct mem_cgroup = *memcg) {} > #define split_huge_pmd(__vma, __pmd, __address) \ > do { } while (0) >=20 > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index bb32091e3133e..5fc0caca71de0 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1094,9 +1094,22 @@ static struct deferred_split = *folio_split_queue_lock(struct folio *folio) > struct deferred_split *queue; >=20 > memcg =3D folio_memcg(folio); > +retry: > queue =3D memcg ? &memcg->deferred_split_queue : > = &NODE_DATA(folio_nid(folio))->deferred_split_queue; > spin_lock(&queue->split_queue_lock); > + /* > + * Notice: > + * 1. The memcg could be NULL if cgroup_disable=3Dmemory is set. > + * 2. There is a period between setting CSS_DYING and = reparenting > + * deferred split queue, and during this period the THPs in = the > + * deferred split queue will be hidden from the shrinker = side. > + */ > + if (unlikely(memcg && css_is_dying(&memcg->css))) { > + spin_unlock(&queue->split_queue_lock); > + memcg =3D parent_mem_cgroup(memcg); > + goto retry; > + } >=20 > return queue; > } > @@ -1108,9 +1121,15 @@ folio_split_queue_lock_irqsave(struct folio = *folio, unsigned long *flags) > struct deferred_split *queue; >=20 > memcg =3D folio_memcg(folio); > +retry: > queue =3D memcg ? &memcg->deferred_split_queue : > = &NODE_DATA(folio_nid(folio))->deferred_split_queue; > spin_lock_irqsave(&queue->split_queue_lock, *flags); > + if (unlikely(memcg && css_is_dying(&memcg->css))) { > + spin_unlock_irqrestore(&queue->split_queue_lock, = *flags); > + memcg =3D parent_mem_cgroup(memcg); > + goto retry; > + } >=20 > return queue; > } > @@ -4275,6 +4294,33 @@ static unsigned long deferred_split_scan(struct = shrinker *shrink, > return split; > } >=20 > +#ifdef CONFIG_MEMCG > +void reparent_deferred_split_queue(struct mem_cgroup *memcg) > +{ > + struct mem_cgroup *parent =3D parent_mem_cgroup(memcg); > + struct deferred_split *ds_queue =3D = &memcg->deferred_split_queue; > + struct deferred_split *parent_ds_queue =3D = &parent->deferred_split_queue; > + int nid; > + > + spin_lock_irq(&ds_queue->split_queue_lock); > + spin_lock_nested(&parent_ds_queue->split_queue_lock, = SINGLE_DEPTH_NESTING); > + > + if (!ds_queue->split_queue_len) > + goto unlock; > + > + list_splice_tail_init(&ds_queue->split_queue, = &parent_ds_queue->split_queue); > + parent_ds_queue->split_queue_len +=3D ds_queue->split_queue_len; > + ds_queue->split_queue_len =3D 0; > + > + for_each_node(nid) > + set_shrinker_bit(parent, nid, = shrinker_id(deferred_split_shrinker)); > + > +unlock: > + spin_unlock(&parent_ds_queue->split_queue_lock); > + spin_unlock_irq(&ds_queue->split_queue_lock); > +} > +#endif > + > #ifdef CONFIG_DEBUG_FS > static void split_huge_pages_all(void) > { > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index e090f29eb03bd..d03da72e7585d 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3887,6 +3887,7 @@ static void mem_cgroup_css_offline(struct = cgroup_subsys_state *css) > zswap_memcg_offline_cleanup(memcg); >=20 > memcg_offline_kmem(memcg); > + reparent_deferred_split_queue(memcg); Since the dying flag of a memcg is not set under split_queue_lock, two threads holding different split_queue_locks (e.g., one for the parent memcg and one for the child) can concurrently manipulate the same split-queue list of a folio. I think we should take the same solution like list_lru does to fix this. Muchun, Thanks. > reparent_shrinker_deferred(memcg); > wb_memcg_offline(memcg); > lru_gen_offline_memcg(memcg); > --=20 > 2.20.1 >=20