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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: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
This commit is contained in:
Sebastian Andrzej Siewior 2021-02-26 17:11:55 +01:00 committed by Vlastimil Babka
parent 08beb547a1
commit 5a836bf6b0
2 changed files with 80 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
mm/slab_common.c
View File

@ -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);

94
mm/slub.c
View File

@ -2496,16 +2496,25 @@ 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);
stat(s, CPUSLAB_FLUSH);
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;