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Mon, 22 Sep 2025 00:56:09 -0700 (PDT) Message-ID: <28f36249-f064-4d32-9d8a-ba03db5b491c@bytedance.com> Date: Mon, 22 Sep 2025 15:56:00 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/4] mm: thp: introduce folio_split_queue_lock and its variants To: Zi Yan Cc: hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, david@redhat.com, lorenzo.stoakes@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, Muchun Song References: From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Zi, On 9/19/25 11:39 PM, Zi Yan wrote: > On 18 Sep 2025, at 23:46, Qi Zheng wrote: > >> From: Muchun Song >> >> In future memcg removal, the binding between a folio and a memcg may >> change, making the split lock within the memcg unstable when held. >> >> A new approach is required to reparent the split queue to its parent. This >> patch starts introducing a unified way to acquire the split lock for >> future work. >> >> It's a code-only refactoring with no functional changes. >> >> Signed-off-by: Muchun Song >> Acked-by: Johannes Weiner >> Signed-off-by: Qi Zheng >> --- >> include/linux/memcontrol.h | 10 +++++ >> mm/huge_memory.c | 89 ++++++++++++++++++++++++++------------ >> 2 files changed, 71 insertions(+), 28 deletions(-) >> >> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >> index 16fe0306e50ea..99876af13c315 100644 >> --- a/include/linux/memcontrol.h >> +++ b/include/linux/memcontrol.h >> @@ -1662,6 +1662,11 @@ int alloc_shrinker_info(struct mem_cgroup *memcg); >> void free_shrinker_info(struct mem_cgroup *memcg); >> void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id); >> void reparent_shrinker_deferred(struct mem_cgroup *memcg); >> + >> +static inline int shrinker_id(struct shrinker *shrinker) >> +{ >> + return shrinker->id; >> +} >> #else >> #define mem_cgroup_sockets_enabled 0 >> >> @@ -1693,6 +1698,11 @@ static inline void set_shrinker_bit(struct mem_cgroup *memcg, >> int nid, int shrinker_id) >> { >> } >> + >> +static inline int shrinker_id(struct shrinker *shrinker) >> +{ >> + return -1; >> +} >> #endif >> >> #ifdef CONFIG_MEMCG >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 582628ddf3f33..d34516a22f5bb 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -1078,26 +1078,62 @@ pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma) >> >> #ifdef CONFIG_MEMCG >> static inline >> -struct deferred_split *get_deferred_split_queue(struct folio *folio) >> +struct mem_cgroup *folio_split_queue_memcg(struct folio *folio, >> + struct deferred_split *queue) >> { >> - struct mem_cgroup *memcg = folio_memcg(folio); >> - struct pglist_data *pgdat = NODE_DATA(folio_nid(folio)); >> - >> - if (memcg) >> - return &memcg->deferred_split_queue; >> - else >> - return &pgdat->deferred_split_queue; >> + if (mem_cgroup_disabled()) >> + return NULL; >> + if (&NODE_DATA(folio_nid(folio))->deferred_split_queue == queue) >> + return NULL; >> + return container_of(queue, struct mem_cgroup, deferred_split_queue); >> } >> #else >> static inline >> -struct deferred_split *get_deferred_split_queue(struct folio *folio) >> +struct mem_cgroup *folio_split_queue_memcg(struct folio *folio, >> + struct deferred_split *queue) >> { >> - struct pglist_data *pgdat = NODE_DATA(folio_nid(folio)); >> - >> - return &pgdat->deferred_split_queue; >> + return NULL; >> } >> #endif >> >> +static struct deferred_split *folio_split_queue_lock(struct folio *folio) >> +{ >> + struct mem_cgroup *memcg; >> + struct deferred_split *queue; >> + >> + memcg = folio_memcg(folio); >> + queue = memcg ? &memcg->deferred_split_queue : >> + &NODE_DATA(folio_nid(folio))->deferred_split_queue; >> + spin_lock(&queue->split_queue_lock); >> + >> + return queue; >> +} >> + >> +static struct deferred_split * >> +folio_split_queue_lock_irqsave(struct folio *folio, unsigned long *flags) >> +{ >> + struct mem_cgroup *memcg; >> + struct deferred_split *queue; >> + >> + memcg = folio_memcg(folio); >> + queue = memcg ? &memcg->deferred_split_queue : >> + &NODE_DATA(folio_nid(folio))->deferred_split_queue; >> + spin_lock_irqsave(&queue->split_queue_lock, *flags); >> + >> + return queue; >> +} > > A helper function to get queue from a folio would get rid of duplicated > code in the two functions above. Hmm, that is the deleted > get_deferred_split_queue(). So probably retain it. After PATCH #4, we may retry after getting parent memcg in the above functions. so we may not need to retrieve get_deferred_split_queue(). > > Otherwise, LGTM. Reviewed-by: Zi Yan Thanks! > > Best Regards, > Yan, Zi