From 54aab23b5557eda17033a5d020be3eada6493aa4 Mon Sep 17 00:00:00 2001
Message-Id: <54aab23b5557eda17033a5d020be3eada6493aa4.1599166690.git.zanussi@kernel.org>
In-Reply-To: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org>
References: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org>
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 21 Jun 2018 17:29:19 +0200
Subject: [PATCH 075/333] mm/SLUB: delay giving back empty slubs to IRQ enabled
 regions
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.142-rt63.tar.xz

__free_slab() is invoked with disabled interrupts which increases the
irq-off time while __free_pages() is doing the work.
Allow __free_slab() to be invoked with enabled interrupts and move
everything from interrupts-off invocations to a temporary per-CPU list
so it can be processed later.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 mm/slub.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 69 insertions(+), 5 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 66416eff4818..b890fe5f9cd3 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1349,6 +1349,12 @@ static bool freelist_corrupted(struct kmem_cache *s, struct page *page,
 }
 #endif /* CONFIG_SLUB_DEBUG */
 
+struct slub_free_list {
+	raw_spinlock_t		lock;
+	struct list_head	list;
+};
+static DEFINE_PER_CPU(struct slub_free_list, slub_free_list);
+
 /*
  * Hooks for other subsystems that check memory allocations. In a typical
  * production configuration these hooks all should produce no code at all.
@@ -1703,6 +1709,16 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
 	__free_pages(page, order);
 }
 
+static void free_delayed(struct list_head *h)
+{
+	while (!list_empty(h)) {
+		struct page *page = list_first_entry(h, struct page, lru);
+
+		list_del(&page->lru);
+		__free_slab(page->slab_cache, page);
+	}
+}
+
 static void rcu_free_slab(struct rcu_head *h)
 {
 	struct page *page = container_of(h, struct page, rcu_head);
@@ -1714,6 +1730,12 @@ static void free_slab(struct kmem_cache *s, struct page *page)
 {
 	if (unlikely(s->flags & SLAB_TYPESAFE_BY_RCU)) {
 		call_rcu(&page->rcu_head, rcu_free_slab);
+	} else if (irqs_disabled()) {
+		struct slub_free_list *f = this_cpu_ptr(&slub_free_list);
+
+		raw_spin_lock(&f->lock);
+		list_add(&page->lru, &f->list);
+		raw_spin_unlock(&f->lock);
 	} else
 		__free_slab(s, page);
 }
@@ -2248,14 +2270,21 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
 			pobjects = oldpage->pobjects;
 			pages = oldpage->pages;
 			if (drain && pobjects > s->cpu_partial) {
+				struct slub_free_list *f;
 				unsigned long flags;
+				LIST_HEAD(tofree);
 				/*
 				 * partial array is full. Move the existing
 				 * set to the per node partial list.
 				 */
 				local_irq_save(flags);
 				unfreeze_partials(s, this_cpu_ptr(s->cpu_slab));
+				f = this_cpu_ptr(&slub_free_list);
+				raw_spin_lock(&f->lock);
+				list_splice_init(&f->list, &tofree);
+				raw_spin_unlock(&f->lock);
 				local_irq_restore(flags);
+				free_delayed(&tofree);
 				oldpage = NULL;
 				pobjects = 0;
 				pages = 0;
@@ -2325,7 +2354,22 @@ static bool has_cpu_slab(int cpu, void *info)
 
 static void flush_all(struct kmem_cache *s)
 {
+	LIST_HEAD(tofree);
+	int cpu;
+
 	on_each_cpu_cond(has_cpu_slab, flush_cpu_slab, s, 1, GFP_ATOMIC);
+	for_each_online_cpu(cpu) {
+		struct slub_free_list *f;
+
+		if (!has_cpu_slab(cpu, s))
+			continue;
+
+		f = &per_cpu(slub_free_list, cpu);
+		raw_spin_lock_irq(&f->lock);
+		list_splice_init(&f->list, &tofree);
+		raw_spin_unlock_irq(&f->lock);
+		free_delayed(&tofree);
+	}
 }
 
 /*
@@ -2523,8 +2567,10 @@ static inline void *get_freelist(struct kmem_cache *s, struct page *page)
  * already disabled (which is the case for bulk allocation).
  */
 static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
-			  unsigned long addr, struct kmem_cache_cpu *c)
+			  unsigned long addr, struct kmem_cache_cpu *c,
+			  struct list_head *to_free)
 {
+	struct slub_free_list *f;
 	void *freelist;
 	struct page *page;
 
@@ -2590,6 +2636,13 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	VM_BUG_ON(!c->page->frozen);
 	c->freelist = get_freepointer(s, freelist);
 	c->tid = next_tid(c->tid);
+
+out:
+	f = this_cpu_ptr(&slub_free_list);
+	raw_spin_lock(&f->lock);
+	list_splice_init(&f->list, to_free);
+	raw_spin_unlock(&f->lock);
+
 	return freelist;
 
 new_slab:
@@ -2605,7 +2658,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 
 	if (unlikely(!freelist)) {
 		slab_out_of_memory(s, gfpflags, node);
-		return NULL;
+		goto out;
 	}
 
 	page = c->page;
@@ -2618,7 +2671,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 		goto new_slab;	/* Slab failed checks. Next slab needed */
 
 	deactivate_slab(s, page, get_freepointer(s, freelist), c);
-	return freelist;
+	goto out;
 }
 
 /*
@@ -2630,6 +2683,7 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 {
 	void *p;
 	unsigned long flags;
+	LIST_HEAD(tofree);
 
 	local_irq_save(flags);
 #ifdef CONFIG_PREEMPT
@@ -2641,8 +2695,9 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	c = this_cpu_ptr(s->cpu_slab);
 #endif
 
-	p = ___slab_alloc(s, gfpflags, node, addr, c);
+	p = ___slab_alloc(s, gfpflags, node, addr, c, &tofree);
 	local_irq_restore(flags);
+	free_delayed(&tofree);
 	return p;
 }
 
@@ -3122,6 +3177,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 			  void **p)
 {
 	struct kmem_cache_cpu *c;
+	LIST_HEAD(to_free);
 	int i;
 
 	/* memcg and kmem_cache debug support */
@@ -3154,7 +3210,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 			 * of re-populating per CPU c->freelist
 			 */
 			p[i] = ___slab_alloc(s, flags, NUMA_NO_NODE,
-					    _RET_IP_, c);
+					    _RET_IP_, c, &to_free);
 			if (unlikely(!p[i]))
 				goto error;
 
@@ -3166,6 +3222,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 	}
 	c->tid = next_tid(c->tid);
 	local_irq_enable();
+	free_delayed(&to_free);
 
 	/* Clear memory outside IRQ disabled fastpath loop */
 	if (unlikely(flags & __GFP_ZERO)) {
@@ -3180,6 +3237,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 	return i;
 error:
 	local_irq_enable();
+	free_delayed(&to_free);
 	slab_post_alloc_hook(s, flags, i, p);
 	__kmem_cache_free_bulk(s, i, p);
 	return 0;
@@ -4229,6 +4287,12 @@ void __init kmem_cache_init(void)
 {
 	static __initdata struct kmem_cache boot_kmem_cache,
 		boot_kmem_cache_node;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		raw_spin_lock_init(&per_cpu(slub_free_list, cpu).lock);
+		INIT_LIST_HEAD(&per_cpu(slub_free_list, cpu).list);
+	}
 
 	if (debug_guardpage_minorder())
 		slub_max_order = 0;
-- 
2.17.1

