Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple kmem_cache_free callback
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: 2024-06-17 14:56:28
Also in:
bridge, kernel-janitors, kvm, linux-block, linux-can, linux-nfs, linuxppc-dev, lkml, netdev, netfilter-devel
Subsystem:
memory management, slab allocator, the rest · Maintainers:
Andrew Morton, Vlastimil Babka, Harry Yoo, Linus Torvalds
On Mon, Jun 17, 2024 at 03:50:56PM +0200, Uladzislau Rezki wrote:
On Fri, Jun 14, 2024 at 09:33:45PM +0200, Jason A. Donenfeld wrote:quoted
On Fri, Jun 14, 2024 at 02:35:33PM +0200, Uladzislau Rezki wrote:quoted
+ /* Should a destroy process be deferred? */ + if (s->flags & SLAB_DEFER_DESTROY) { + list_move_tail(&s->list, &slab_caches_defer_destroy); + schedule_delayed_work(&slab_caches_defer_destroy_work, HZ); + goto out_unlock; + }Wouldn't it be smoother to have the actual kmem_cache_free() function check to see if it's been marked for destruction and the refcount is zero, rather than polling every one second? I mentioned this approach in: https://lore.kernel.org/all/Zmo9-YGraiCj5-MI@zx2c4.com/ (local) - I wonder if the right fix to this would be adding a `should_destroy` boolean to kmem_cache, which kmem_cache_destroy() sets to true. And then right after it checks `if (number_of_allocations == 0) actually_destroy()`, and likewise on each kmem_cache_free(), it could check `if (should_destroy && number_of_allocations == 0) actually_destroy()`.I do not find pooling as bad way we can go with. But your proposal sounds reasonable to me also. We can combine both "prototypes" to one and offer. Can you post a prototype here?
This is untested, but the simplest, shortest possible version would be:
diff --git a/mm/slab.h b/mm/slab.h
index 5f8f47c5bee0..907c0ea56c01 100644
--- a/mm/slab.h
+++ b/mm/slab.h@@ -275,6 +275,7 @@ struct kmem_cache { unsigned int inuse; /* Offset to metadata */ unsigned int align; /* Alignment */ unsigned int red_left_pad; /* Left redzone padding size */ + bool is_destroyed; /* Destruction happens when no objects */ const char *name; /* Name (only for display!) */ struct list_head list; /* List of slab caches */ #ifdef CONFIG_SYSFS
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 1560a1546bb1..f700bed066d9 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c@@ -494,8 +494,8 @@ void kmem_cache_destroy(struct kmem_cache *s) goto out_unlock; err = shutdown_cache(s); - WARN(err, "%s %s: Slab cache still has objects when called from %pS", - __func__, s->name, (void *)_RET_IP_); + if (err) + s->is_destroyed = true; out_unlock: mutex_unlock(&slab_mutex); cpus_read_unlock();
diff --git a/mm/slub.c b/mm/slub.c
index 1373ac365a46..7db8fe90a323 100644
--- a/mm/slub.c
+++ b/mm/slub.c@@ -4510,6 +4510,8 @@ void kmem_cache_free(struct kmem_cache *s, void *x) return; trace_kmem_cache_free(_RET_IP_, x, s); slab_free(s, virt_to_slab(x), x, _RET_IP_); + if (s->is_destroyed) + kmem_cache_destroy(s); } EXPORT_SYMBOL(kmem_cache_free);
@@ -5342,9 +5344,6 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n) if (!slab->inuse) { remove_partial(n, slab); list_add(&slab->slab_list, &discard); - } else { - list_slab_objects(s, slab, - "Objects remaining in %s on __kmem_cache_shutdown()"); } } spin_unlock_irq(&n->list_lock);