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Date: Sat, 4 Sep 2021 12:49:58 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: linux-mm@...ck.org, Christoph Lameter <cl@...ux.com>,
David Rientjes <rientjes@...gle.com>,
Pekka Enberg <penberg@...nel.org>,
Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, Mike Galbraith <efault@....de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Thomas Gleixner <tglx@...utronix.de>,
Mel Gorman <mgorman@...hsingularity.net>,
Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH v6 28/33] mm: slub: move flush_cpu_slab() invocations __free_slab() invocations out of IRQ context
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
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@...e.cz: adapt to new SLUB changes]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
mm/slab_common.c | 2 ++
mm/slub.c | 94 +++++++++++++++++++++++++++++++++++++++---------
2 files changed, 80 insertions(+), 16 deletions(-)
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 1c673c323baf..ec2bb0beed75 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -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);
diff --git a/mm/slub.c b/mm/slub.c
index fa9a366d2d9c..b7f8b9d34e46 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -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;
--
2.33.0
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