From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Subject: 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@xxxxxxx: adapt to new SLUB changes] Link: https://lkml.kernel.org/r/20210904105003.11688-29-vbabka@xxxxxxx Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Qian Cai <quic_qiancai@xxxxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Mike Galbraith <efault@xxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/slab_common.c | 2 mm/slub.c | 94 +++++++++++++++++++++++++++++++++++++-------- 2 files changed, 80 insertions(+), 16 deletions(-) --- a/mm/slab_common.c~mm-slub-move-flush_cpu_slab-invocations-__free_slab-invocations-out-of-irq-context +++ a/mm/slab_common.c @@ -502,6 +502,7 @@ void kmem_cache_destroy(struct kmem_cach if (unlikely(!s)) return; + cpus_read_lock(); mutex_lock(&slab_mutex); s->refcount--; @@ -516,6 +517,7 @@ void kmem_cache_destroy(struct kmem_cach } out_unlock: mutex_unlock(&slab_mutex); + cpus_read_unlock(); } EXPORT_SYMBOL(kmem_cache_destroy); --- a/mm/slub.c~mm-slub-move-flush_cpu_slab-invocations-__free_slab-invocations-out-of-irq-context +++ a/mm/slub.c @@ -2496,16 +2496,25 @@ static void put_cpu_partial(struct kmem_ 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(stru 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_ca 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_cach 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_cach 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; _
