Commit 5a836bf6 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Vlastimil Babka
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mm: slub: move flush_cpu_slab() invocations __free_slab() invocations out of IRQ context 



flush_all() flushes a specific SLAB cache on each CPU (where the cache
is present). The deactivate_slab()/__free_slab() invocation happens
within IPI handler and is problematic for PREEMPT_RT.

The flush operation is not a frequent operation or a hot path. The
per-CPU flush operation can be moved to within a workqueue.

Because a workqueue handler, unlike IPI handler, does not disable irqs,
flush_slab() now has to disable them for working with the kmem_cache_cpu
fields. deactivate_slab() is safe to call with irqs enabled.

[vbabka@suse.cz: adapt to new SLUB changes]
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
parent 08beb547

mm/slab_common.c

+2 −0
Original line number Diff line number Diff line
@@ -502,6 +502,7 @@ void kmem_cache_destroy(struct kmem_cache *s) 
	if (unlikely(!s))

		return;



	cpus_read_lock();

	mutex_lock(&slab_mutex);



	s->refcount--;
@@ -516,6 +517,7 @@ void kmem_cache_destroy(struct kmem_cache *s) 
	}

out_unlock:

	mutex_unlock(&slab_mutex);

	cpus_read_unlock();

}

EXPORT_SYMBOL(kmem_cache_destroy);

mm/slub.c

+78 −16
Original line number Diff line number Diff line
@@ -2496,17 +2496,26 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain) 


static inline void flush_slab(struct kmem_cache *s, struct kmem_cache_cpu *c)

{

	void *freelist = c->freelist;

	struct page *page = c->page;

	unsigned long flags;

	struct page *page;

	void *freelist;



	local_irq_save(flags);



	page = c->page;

	freelist = c->freelist;



	c->page = NULL;

	c->freelist = NULL;

	c->tid = next_tid(c->tid);



	deactivate_slab(s, page, freelist);

	local_irq_restore(flags);



	if (page) {

		deactivate_slab(s, page, freelist);

		stat(s, CPUSLAB_FLUSH);

	}

}



static inline void __flush_cpu_slab(struct kmem_cache *s, int cpu)

{
@@ -2526,15 +2535,27 @@ static inline void __flush_cpu_slab(struct kmem_cache *s, int cpu) 
	unfreeze_partials_cpu(s, c);

}



struct slub_flush_work {

	struct work_struct work;

	struct kmem_cache *s;

	bool skip;

};



/*

 * Flush cpu slab.

 *

 * Called from IPI handler with interrupts disabled.

 * Called from CPU work handler with migration disabled.

 */

static void flush_cpu_slab(void *d)

static void flush_cpu_slab(struct work_struct *w)

{

	struct kmem_cache *s = d;

	struct kmem_cache_cpu *c = this_cpu_ptr(s->cpu_slab);

	struct kmem_cache *s;

	struct kmem_cache_cpu *c;

	struct slub_flush_work *sfw;



	sfw = container_of(w, struct slub_flush_work, work);



	s = sfw->s;

	c = this_cpu_ptr(s->cpu_slab);



	if (c->page)

		flush_slab(s, c);
@@ -2542,17 +2563,51 @@ static void flush_cpu_slab(void *d) 
	unfreeze_partials(s);

}



static bool has_cpu_slab(int cpu, void *info)

static bool has_cpu_slab(int cpu, struct kmem_cache *s)

{

	struct kmem_cache *s = info;

	struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);



	return c->page || slub_percpu_partial(c);

}



static DEFINE_MUTEX(flush_lock);

static DEFINE_PER_CPU(struct slub_flush_work, slub_flush);



static void flush_all_cpus_locked(struct kmem_cache *s)

{

	struct slub_flush_work *sfw;

	unsigned int cpu;



	lockdep_assert_cpus_held();

	mutex_lock(&flush_lock);



	for_each_online_cpu(cpu) {

		sfw = &per_cpu(slub_flush, cpu);

		if (!has_cpu_slab(cpu, s)) {

			sfw->skip = true;

			continue;

		}

		INIT_WORK(&sfw->work, flush_cpu_slab);

		sfw->skip = false;

		sfw->s = s;

		schedule_work_on(cpu, &sfw->work);

	}



	for_each_online_cpu(cpu) {

		sfw = &per_cpu(slub_flush, cpu);

		if (sfw->skip)

			continue;

		flush_work(&sfw->work);

	}



	mutex_unlock(&flush_lock);

}



static void flush_all(struct kmem_cache *s)

{

	on_each_cpu_cond(has_cpu_slab, flush_cpu_slab, s, 1);

	cpus_read_lock();

	flush_all_cpus_locked(s);

	cpus_read_unlock();

}



/*
@@ -4097,7 +4152,7 @@ int __kmem_cache_shutdown(struct kmem_cache *s) 
	int node;

	struct kmem_cache_node *n;



	flush_all(s);

	flush_all_cpus_locked(s);

	/* Attempt to free all objects */

	for_each_kmem_cache_node(s, node, n) {

		free_partial(s, n);
@@ -4373,7 +4428,7 @@ EXPORT_SYMBOL(kfree); 
 * being allocated from last increasing the chance that the last objects

 * are freed in them.

 */

int __kmem_cache_shrink(struct kmem_cache *s)

static int __kmem_cache_do_shrink(struct kmem_cache *s)

{

	int node;

	int i;
@@ -4385,7 +4440,6 @@ int __kmem_cache_shrink(struct kmem_cache *s) 
	unsigned long flags;

	int ret = 0;



	flush_all(s);

	for_each_kmem_cache_node(s, node, n) {

		INIT_LIST_HEAD(&discard);

		for (i = 0; i < SHRINK_PROMOTE_MAX; i++)
@@ -4435,13 +4489,21 @@ int __kmem_cache_shrink(struct kmem_cache *s) 
	return ret;

}



int __kmem_cache_shrink(struct kmem_cache *s)

{

	flush_all(s);

	return __kmem_cache_do_shrink(s);

}



static int slab_mem_going_offline_callback(void *arg)

{

	struct kmem_cache *s;



	mutex_lock(&slab_mutex);

	list_for_each_entry(s, &slab_caches, list)

		__kmem_cache_shrink(s);

	list_for_each_entry(s, &slab_caches, list) {

		flush_all_cpus_locked(s);

		__kmem_cache_do_shrink(s);

	}

	mutex_unlock(&slab_mutex);



	return 0;