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Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kairui Song , Qi Zheng , Shakeel Butt , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , "Paul E . McKenney" , Pedro Falcato , Harry Yoo , Luis Chamberlain , Ilya Gladyshev , Jaegeuk Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, fuse-devel@lists.linux.dev, kernel-team@meta.com Subject: [RFC PATCH 04/18] mm: count the pages waiting for a grace period Date: Mon, 19 Oct 2026 16:48:57 +0100 Message-ID: <20261019154913.1765974-5-kas@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20261019154913.1765974-1-kas@kernel.org> References: <20261019154913.1765974-1-kas@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Deferred folios have refcount 0 and are not on the free lists, so no counter shows them. Memory that waits for a grace period is missing from the free count and from every LRU count. Count it per zone in NR_FREE_RCU_PAGES: nr_free_rcu in /proc/vmstat, free_rcu in show_free_areas(). Preparation for freeing the waiting pages sooner when they hold back memory that is needed. Assisted-by: LLM Signed-off-by: Kiryl Shutsemau (Meta) --- include/linux/mmzone.h | 1 + mm/page_alloc.c | 4 ++++ mm/show_mem.c | 9 ++++++--- mm/vmstat.c | 2 ++ 4 files changed, 13 insertions(+), 3 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 94f9c3ff5416..3336b9e5ee99 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -228,6 +228,7 @@ enum zone_stat_item { NR_ZSPAGES, /* allocated in zsmalloc */ #endif NR_FREE_CMA_PAGES, + NR_FREE_RCU_PAGES, /* freed, waiting for an RCU grace period */ #ifdef CONFIG_UNACCEPTED_MEMORY NR_UNACCEPTED, #endif diff --git a/mm/page_alloc.c b/mm/page_alloc.c index a371e92da273..15bb66e36304 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1348,6 +1348,8 @@ static void rcu_free_pages(struct list_head *list) folio_batch_init(&fbatch); list_for_each_entry_safe(folio, next, list, lru) { + mod_zone_page_state(folio_zone(folio), NR_FREE_RCU_PAGES, + -folio_nr_pages(folio)); if (!folio_batch_add(&fbatch, folio)) { free_unref_folios(&fbatch); cond_resched_tasks_rcu_qs(); @@ -1375,9 +1377,11 @@ static void rcu_free_workfn(struct work_struct *work) static void rcu_free_defer(struct folio *folio) { struct rcu_free_pcpu *r = raw_cpu_ptr(&rcu_free_pcpu); + struct zone *zone = folio_zone(folio); unsigned long flags; spin_lock_irqsave(&r->lock, flags); + __mod_zone_page_state(zone, NR_FREE_RCU_PAGES, folio_nr_pages(folio)); list_add_tail(&folio->lru, &r->pending); rcu_free_start(r); spin_unlock_irqrestore(&r->lock, flags); diff --git a/mm/show_mem.c b/mm/show_mem.c index b938cbcd774a..0d3bddbda108 100644 --- a/mm/show_mem.c +++ b/mm/show_mem.c @@ -204,7 +204,7 @@ static void show_free_areas(unsigned int filter, const nodemask_t *nodemask, " mapped:%lu shmem:%lu pagetables:%lu\n" " sec_pagetables:%lu bounce:%lu\n" " kernel_misc_reclaimable:%lu\n" - " free:%lu free_pcp:%lu free_cma:%lu\n", + " free:%lu free_pcp:%lu free_cma:%lu free_rcu:%lu\n", global_node_page_state(NR_ACTIVE_ANON), global_node_page_state(NR_INACTIVE_ANON), global_node_page_state(NR_ISOLATED_ANON), @@ -224,7 +224,8 @@ static void show_free_areas(unsigned int filter, const nodemask_t *nodemask, global_node_page_state(NR_KERNEL_MISC_RECLAIMABLE), global_zone_page_state(NR_FREE_PAGES), free_pcp, - global_zone_page_state(NR_FREE_CMA_PAGES)); + global_zone_page_state(NR_FREE_CMA_PAGES), + global_zone_page_state(NR_FREE_RCU_PAGES)); for_each_online_pgdat(pgdat) { if (show_mem_node_skip(filter, pgdat->node_id, nodemask)) @@ -325,6 +326,7 @@ static void show_free_areas(unsigned int filter, const nodemask_t *nodemask, " free_pcp:%lukB" " local_pcp:%lukB" " free_cma:%lukB" + " free_rcu:%lukB" "\n", zone->name, K(zone_page_state(zone, NR_FREE_PAGES)), @@ -351,7 +353,8 @@ static void show_free_areas(unsigned int filter, const nodemask_t *nodemask, 0UL, K(free_pcp), K((unsigned long)this_cpu_read(zone->per_cpu_pageset->count)), - K(zone_page_state(zone, NR_FREE_CMA_PAGES))); + K(zone_page_state(zone, NR_FREE_CMA_PAGES)), + K(zone_page_state(zone, NR_FREE_RCU_PAGES))); printk("lowmem_reserve[]:"); for (i = 0; i < MAX_NR_ZONES; i++) printk(KERN_CONT " %ld", zone->lowmem_reserve[i]); diff --git a/mm/vmstat.c b/mm/vmstat.c index 66ed017bde46..64068d73d6d2 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1212,6 +1212,7 @@ const char * const vmstat_text[] = { [I(NR_ZSPAGES)] = "nr_zspages", #endif [I(NR_FREE_CMA_PAGES)] = "nr_free_cma", + [I(NR_FREE_RCU_PAGES)] = "nr_free_rcu", #ifdef CONFIG_UNACCEPTED_MEMORY [I(NR_UNACCEPTED)] = "nr_unaccepted", #endif @@ -2023,6 +2024,7 @@ static int vmstat_refresh(const struct ctl_table *table, int write, switch (i) { case NR_ZONE_WRITE_PENDING: case NR_FREE_CMA_PAGES: + case NR_FREE_RCU_PAGES: continue; } val = atomic_long_read(&vm_zone_stat[i]); -- 2.54.0