From: Harry Yoo Date: Sun, 7 Dec 2025 15:41:47 +0000 (+0900) Subject: mm/slab: introduce kvfree_rcu_barrier_on_cache() for cache destruction X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0f35040de59371ad542b915d7b91176c9910dadc;p=thirdparty%2Fkernel%2Flinux.git mm/slab: introduce kvfree_rcu_barrier_on_cache() for cache destruction Currently, kvfree_rcu_barrier() flushes RCU sheaves across all slab caches when a cache is destroyed. This is unnecessary; only the RCU sheaves belonging to the cache being destroyed need to be flushed. As suggested by Vlastimil Babka, introduce a weaker form of kvfree_rcu_barrier() that operates on a specific slab cache. Factor out flush_rcu_sheaves_on_cache() from flush_all_rcu_sheaves() and call it from flush_all_rcu_sheaves() and kvfree_rcu_barrier_on_cache(). Call kvfree_rcu_barrier_on_cache() instead of kvfree_rcu_barrier() on cache destruction. The performance benefit is evaluated on a 12 core 24 threads AMD Ryzen 5900X machine (1 socket), by loading slub_kunit module. Before: Total calls: 19 Average latency (us): 18127 Total time (us): 344414 After: Total calls: 19 Average latency (us): 10066 Total time (us): 191264 Two performance regression have been reported: - stress module loader test's runtime increases by 50-60% (Daniel) - internal graphics test's runtime on Tegra234 increases by 35% (Jon) They are fixed by this change. Suggested-by: Vlastimil Babka Fixes: ec66e0d59952 ("slab: add sheaf support for batching kfree_rcu() operations") Cc: stable@vger.kernel.org Link: https://lore.kernel.org/linux-mm/1bda09da-93be-4737-aef0-d47f8c5c9301@suse.cz Reported-and-tested-by: Daniel Gomez Closes: https://lore.kernel.org/linux-mm/0406562e-2066-4cf8-9902-b2b0616dd742@kernel.org Reported-and-tested-by: Jon Hunter Closes: https://lore.kernel.org/linux-mm/e988eff6-1287-425e-a06c-805af5bbf262@nvidia.com Signed-off-by: Harry Yoo Link: https://patch.msgid.link/20251207154148.117723-1-harry.yoo@oracle.com Signed-off-by: Vlastimil Babka --- diff --git a/include/linux/slab.h b/include/linux/slab.h index cf443f064a667..2482992248dc9 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -1150,10 +1150,17 @@ static inline void kvfree_rcu_barrier(void) rcu_barrier(); } +static inline void kvfree_rcu_barrier_on_cache(struct kmem_cache *s) +{ + rcu_barrier(); +} + static inline void kfree_rcu_scheduler_running(void) { } #else void kvfree_rcu_barrier(void); +void kvfree_rcu_barrier_on_cache(struct kmem_cache *s); + void kfree_rcu_scheduler_running(void); #endif diff --git a/mm/slab.h b/mm/slab.h index f730e012553cc..e767aa7e91b09 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -422,6 +422,7 @@ static inline bool is_kmalloc_normal(struct kmem_cache *s) bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj); void flush_all_rcu_sheaves(void); +void flush_rcu_sheaves_on_cache(struct kmem_cache *s); #define SLAB_CORE_FLAGS (SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA | \ SLAB_CACHE_DMA32 | SLAB_PANIC | \ diff --git a/mm/slab_common.c b/mm/slab_common.c index 84dfff4f7b1fc..dd8a49d6f9cc3 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -492,7 +492,7 @@ void kmem_cache_destroy(struct kmem_cache *s) return; /* in-flight kfree_rcu()'s may include objects from our cache */ - kvfree_rcu_barrier(); + kvfree_rcu_barrier_on_cache(s); if (IS_ENABLED(CONFIG_SLUB_RCU_DEBUG) && (s->flags & SLAB_TYPESAFE_BY_RCU)) { @@ -2038,25 +2038,13 @@ unlock_return: } EXPORT_SYMBOL_GPL(kvfree_call_rcu); -/** - * kvfree_rcu_barrier - Wait until all in-flight kvfree_rcu() complete. - * - * Note that a single argument of kvfree_rcu() call has a slow path that - * triggers synchronize_rcu() following by freeing a pointer. It is done - * before the return from the function. Therefore for any single-argument - * call that will result in a kfree() to a cache that is to be destroyed - * during module exit, it is developer's responsibility to ensure that all - * such calls have returned before the call to kmem_cache_destroy(). - */ -void kvfree_rcu_barrier(void) +static inline void __kvfree_rcu_barrier(void) { struct kfree_rcu_cpu_work *krwp; struct kfree_rcu_cpu *krcp; bool queued; int i, cpu; - flush_all_rcu_sheaves(); - /* * Firstly we detach objects and queue them over an RCU-batch * for all CPUs. Finally queued works are flushed for each CPU. @@ -2118,8 +2106,43 @@ void kvfree_rcu_barrier(void) } } } + +/** + * kvfree_rcu_barrier - Wait until all in-flight kvfree_rcu() complete. + * + * Note that a single argument of kvfree_rcu() call has a slow path that + * triggers synchronize_rcu() following by freeing a pointer. It is done + * before the return from the function. Therefore for any single-argument + * call that will result in a kfree() to a cache that is to be destroyed + * during module exit, it is developer's responsibility to ensure that all + * such calls have returned before the call to kmem_cache_destroy(). + */ +void kvfree_rcu_barrier(void) +{ + flush_all_rcu_sheaves(); + __kvfree_rcu_barrier(); +} EXPORT_SYMBOL_GPL(kvfree_rcu_barrier); +/** + * kvfree_rcu_barrier_on_cache - Wait for in-flight kvfree_rcu() calls on a + * specific slab cache. + * @s: slab cache to wait for + * + * See the description of kvfree_rcu_barrier() for details. + */ +void kvfree_rcu_barrier_on_cache(struct kmem_cache *s) +{ + if (s->cpu_sheaves) + flush_rcu_sheaves_on_cache(s); + /* + * TODO: Introduce a version of __kvfree_rcu_barrier() that works + * on a specific slab cache. + */ + __kvfree_rcu_barrier(); +} +EXPORT_SYMBOL_GPL(kvfree_rcu_barrier_on_cache); + static unsigned long kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) { @@ -2215,4 +2238,3 @@ void __init kvfree_rcu_init(void) } #endif /* CONFIG_KVFREE_RCU_BATCHED */ - diff --git a/mm/slub.c b/mm/slub.c index 2acce22590f84..f22ba8be29e06 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -4122,42 +4122,47 @@ static void flush_rcu_sheaf(struct work_struct *w) /* needed for kvfree_rcu_barrier() */ -void flush_all_rcu_sheaves(void) +void flush_rcu_sheaves_on_cache(struct kmem_cache *s) { struct slub_flush_work *sfw; - struct kmem_cache *s; unsigned int cpu; - cpus_read_lock(); - mutex_lock(&slab_mutex); + mutex_lock(&flush_lock); - list_for_each_entry(s, &slab_caches, list) { - if (!s->cpu_sheaves) - continue; + for_each_online_cpu(cpu) { + sfw = &per_cpu(slub_flush, cpu); - mutex_lock(&flush_lock); + /* + * we don't check if rcu_free sheaf exists - racing + * __kfree_rcu_sheaf() might have just removed it. + * by executing flush_rcu_sheaf() on the cpu we make + * sure the __kfree_rcu_sheaf() finished its call_rcu() + */ - for_each_online_cpu(cpu) { - sfw = &per_cpu(slub_flush, cpu); + INIT_WORK(&sfw->work, flush_rcu_sheaf); + sfw->s = s; + queue_work_on(cpu, flushwq, &sfw->work); + } - /* - * we don't check if rcu_free sheaf exists - racing - * __kfree_rcu_sheaf() might have just removed it. - * by executing flush_rcu_sheaf() on the cpu we make - * sure the __kfree_rcu_sheaf() finished its call_rcu() - */ + for_each_online_cpu(cpu) { + sfw = &per_cpu(slub_flush, cpu); + flush_work(&sfw->work); + } - INIT_WORK(&sfw->work, flush_rcu_sheaf); - sfw->s = s; - queue_work_on(cpu, flushwq, &sfw->work); - } + mutex_unlock(&flush_lock); +} - for_each_online_cpu(cpu) { - sfw = &per_cpu(slub_flush, cpu); - flush_work(&sfw->work); - } +void flush_all_rcu_sheaves(void) +{ + struct kmem_cache *s; + + cpus_read_lock(); + mutex_lock(&slab_mutex); - mutex_unlock(&flush_lock); + list_for_each_entry(s, &slab_caches, list) { + if (!s->cpu_sheaves) + continue; + flush_rcu_sheaves_on_cache(s); } mutex_unlock(&slab_mutex);