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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1758705841; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Wzo9Dce6E9bbwacKQ1Ls7mKYPDh+vWG+TtUgCH/OXas=; b=pTSQvpMOMjgXR64fDZuX0h3oxFz000s6Zr4Ovo6DPMsm1S5N8H8RS0PBUenEQIWyqabi4n rWKzQRXKWeCwCui0yJfERDJiGtQSaY7oxafIm5sfifcNNC0J1B2rfaXfIcmvtRzPDIsuLg SnJeD0BWSWGTvXOWCde/Zfqt48JVv18= From: Roman Gushchin To: Qi Zheng Cc: hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, shakeel.butt@linux.dev, muchun.song@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 Subject: Re: [PATCH v2 4/4] mm: thp: reparent the split queue during memcg offline In-Reply-To: <55370bda7b2df617033ac12116c1712144bb7591.1758618527.git.zhengqi.arch@bytedance.com> (Qi Zheng's message of "Tue, 23 Sep 2025 17:16:25 +0800") References: <55370bda7b2df617033ac12116c1712144bb7591.1758618527.git.zhengqi.arch@bytedance.com> Date: Wed, 24 Sep 2025 09:23:49 +0000 Message-ID: <7ia4bjn06w62.fsf@castle.c.googlers.com> MIME-Version: 1.0 Content-Type: text/plain X-Migadu-Flow: FLOW_OUT X-Stat-Signature: 85pwut1cjeje7kkttfa6z6baht4xi4cs X-Rspam-User: X-Rspamd-Queue-Id: C137E10000D X-Rspamd-Server: rspam10 X-HE-Tag: 1758705843-558525 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Qi Zheng writes: > In the future, we will reparent LRU folios during memcg offline to > eliminate dying memory cgroups, which requires reparenting the split queue > to its parent. Nit: commit logs should really focus on the actual change, not the future plans. > > 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. > > Signed-off-by: Qi Zheng > --- > include/linux/huge_mm.h | 2 ++ > include/linux/mmzone.h | 1 + > mm/huge_memory.c | 39 +++++++++++++++++++++++++++++++++++++++ > mm/memcontrol.c | 1 + > mm/mm_init.c | 1 + > 5 files changed, 44 insertions(+) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index f327d62fc9852..a0d4b751974d2 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -417,6 +417,7 @@ 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); > +void reparent_deferred_split_queue(struct mem_cgroup *memcg); > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > unsigned long address, bool freeze); > @@ -611,6 +612,7 @@ static inline int try_folio_split(struct folio *folio, struct page *page, > } > > 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) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 7fb7331c57250..f3eb81fee056a 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1346,6 +1346,7 @@ struct deferred_split { > spinlock_t split_queue_lock; > struct list_head split_queue; > unsigned long split_queue_len; > + bool is_dying; > }; > #endif > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 48b51e6230a67..de7806f759cba 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1094,9 +1094,15 @@ static struct deferred_split *folio_split_queue_lock(struct folio *folio) > struct deferred_split *queue; > > memcg = folio_memcg(folio); > +retry: > queue = memcg ? &memcg->deferred_split_queue : > &NODE_DATA(folio_nid(folio))->deferred_split_queue; > spin_lock(&queue->split_queue_lock); > + if (unlikely(queue->is_dying == true)) { > + spin_unlock(&queue->split_queue_lock); > + memcg = parent_mem_cgroup(memcg); > + goto retry; > + } > > return queue; > } > @@ -1108,9 +1114,15 @@ folio_split_queue_lock_irqsave(struct folio *folio, unsigned long *flags) > struct deferred_split *queue; > > memcg = folio_memcg(folio); > +retry: > queue = memcg ? &memcg->deferred_split_queue : > &NODE_DATA(folio_nid(folio))->deferred_split_queue; > spin_lock_irqsave(&queue->split_queue_lock, *flags); > + if (unlikely(queue->is_dying == true)) { > + spin_unlock_irqrestore(&queue->split_queue_lock, *flags); > + memcg = parent_mem_cgroup(memcg); > + goto retry; > + } > > return queue; > } > @@ -4284,6 +4296,33 @@ static unsigned long deferred_split_scan(struct shrinker *shrink, > return split; > } > > +void reparent_deferred_split_queue(struct mem_cgroup *memcg) > +{ > + struct mem_cgroup *parent = parent_mem_cgroup(memcg); > + struct deferred_split *ds_queue = &memcg->deferred_split_queue; > + struct deferred_split *parent_ds_queue = &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 += ds_queue->split_queue_len; > + ds_queue->split_queue_len = 0; > + /* Mark the ds_queue dead */ > + ds_queue->is_dying = true; > + > + for_each_node(nid) > + set_shrinker_bit(parent, nid, shrinker_id(deferred_split_shrinker)); Does this loop need to be under locks? > + > +unlock: > + spin_unlock(&parent_ds_queue->split_queue_lock); > + spin_unlock_irq(&ds_queue->split_queue_lock); > +} > + > #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); > > memcg_offline_kmem(memcg); > + reparent_deferred_split_queue(memcg); > reparent_shrinker_deferred(memcg); I guess the naming can be a bit more consistent here :) Thanks!