Extend the sheaf infrastructure for more efficient kfree_rcu() handling.
For caches with sheaves, on each cpu maintain a rcu_free sheaf in
addition to main and spare sheaves.
kfree_rcu() operations will try to put objects on this sheaf. Once full,
the sheaf is detached and submitted to call_rcu() with a handler that
will try to put in in the barn, or flush to slab pages using bulk free,
when the barn is full. Then a new empty sheaf must be obtained to put
more objects there.
It's possible that no free sheaves are available to use for a new
rcu_free sheaf, and the allocation in kfree_rcu() context can only use
GFP_NOWAIT and thus may fail. In that case, fall back to the existing
kfree_rcu() machinery.
Expected advantages:
- batching the kfree_rcu() operations, that could eventually replace the
existing batching
- sheaves can be reused for allocations via barn instead of being
flushed to slabs, which is more efficient
- this includes cases where only some cpus are allowed to process rcu
callbacks (Android)
Possible disadvantage:
- objects might be waiting for more than their grace period (it is
determined by the last object freed into the sheaf), increasing memory
usage - but the existing batching does that too?
Only implement this for CONFIG_KVFREE_RCU_BATCHED as the tiny
implementation favors smaller memory footprint over performance.
Signed-off-by: Vlastimil Babka <vba...@suse.cz>
---
mm/slab.h | 2 +
mm/slab_common.c | 21 ++++++++
mm/slub.c | 151 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
3 files changed, 170 insertions(+), 4 deletions(-)
diff --git a/mm/slab.h b/mm/slab.h
index
8daaec53b6ecfc44171191d421adb12e5cba2c58..94e9959e1aefa350d3d74e3f5309fde7a5cf2ec8
100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -459,6 +459,8 @@ static inline bool is_kmalloc_normal(struct kmem_cache *s)
return !(s->flags & (SLAB_CACHE_DMA|SLAB_ACCOUNT|SLAB_RECLAIM_ACCOUNT));
}
+bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj);
+
/* Legal flag mask for kmem_cache_create(), for various configurations */
#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
ceeefb287899a82f30ad79b403556001c1860311..c6853450ed74160cfcb497c09f92c1f9f7b12629
100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1613,6 +1613,24 @@ static void kfree_rcu_work(struct work_struct *work)
kvfree_rcu_list(head);
}
+static bool kfree_rcu_sheaf(void *obj)
+{
+ struct kmem_cache *s;
+ struct folio *folio;
+ struct slab *slab;
+
+ folio = virt_to_folio(obj);
+ if (unlikely(!folio_test_slab(folio)))
+ return false;
+
+ slab = folio_slab(folio);
+ s = slab->slab_cache;
+ if (s->cpu_sheaves)
+ return __kfree_rcu_sheaf(s, obj);
+
+ return false;
+}
+
static bool
need_offload_krc(struct kfree_rcu_cpu *krcp)
{
@@ -1957,6 +1975,9 @@ void kvfree_call_rcu(struct rcu_head *head, void *ptr)
if (!head)
might_sleep();
+ if (kfree_rcu_sheaf(ptr))
+ return;
+
// Queue the object but don't yet schedule the batch.
if (debug_rcu_head_queue(ptr)) {
// Probable double kfree_rcu(), just leak.
diff --git a/mm/slub.c b/mm/slub.c
index
c06734912972b799f537359f7fe6a750918ffe9e..40175747212fefb27137309b27571abe8d0966e2
100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -350,6 +350,8 @@ enum stat_item {
ALLOC_FASTPATH, /* Allocation from cpu slab */
ALLOC_SLOWPATH, /* Allocation by getting a new cpu slab */
FREE_PCS, /* Free to percpu sheaf */
+ FREE_RCU_SHEAF, /* Free to rcu_free sheaf */
+ FREE_RCU_SHEAF_FAIL, /* Failed to free to a rcu_free sheaf */
FREE_FASTPATH, /* Free to cpu slab */
FREE_SLOWPATH, /* Freeing not to cpu slab */
FREE_FROZEN, /* Freeing to frozen slab */
@@ -2569,6 +2571,24 @@ static void sheaf_flush(struct kmem_cache *s, struct
slab_sheaf *sheaf)
sheaf->size = 0;
}
+static void __rcu_free_sheaf_prepare(struct kmem_cache *s,
+ struct slab_sheaf *sheaf);
+
+static void rcu_free_sheaf_nobarn(struct rcu_head *head)
+{
+ struct slab_sheaf *sheaf;
+ struct kmem_cache *s;
+
+ sheaf = container_of(head, struct slab_sheaf, rcu_head);
+ s = sheaf->cache;
+
+ __rcu_free_sheaf_prepare(s, sheaf);
+
+ sheaf_flush(s, sheaf);
+
+ free_empty_sheaf(s, sheaf);
+}
+
/*
* Caller needs to make sure migration is disabled in order to fully flush
* single cpu's sheaves
@@ -2598,8 +2618,8 @@ static void pcs_flush_all(struct kmem_cache *s)
free_empty_sheaf(s, spare);
}
- // TODO: handle rcu_free
- BUG_ON(rcu_free);
+ if (rcu_free)
+ call_rcu(&rcu_free->rcu_head, rcu_free_sheaf_nobarn);
sheaf_flush_main(s);
}
@@ -2616,8 +2636,10 @@ static void __pcs_flush_all_cpu(struct kmem_cache *s,
unsigned int cpu)
pcs->spare = NULL;
}
- // TODO: handle rcu_free
- BUG_ON(pcs->rcu_free);
+ if (pcs->rcu_free) {
+ call_rcu(&pcs->rcu_free->rcu_head, rcu_free_sheaf_nobarn);
+ pcs->rcu_free = NULL;
+ }
sheaf_flush_main(s);
}
@@ -5192,6 +5214,118 @@ void free_to_pcs(struct kmem_cache *s, void *object)
stat(s, FREE_PCS);
}
+static void __rcu_free_sheaf_prepare(struct kmem_cache *s,
+ struct slab_sheaf *sheaf)
+{
+ bool init = slab_want_init_on_free(s);
+ void **p = &sheaf->objects[0];
+ unsigned int i = 0;
+
+ while (i < sheaf->size) {
+ struct slab *slab = virt_to_slab(p[i]);
+
+ memcg_slab_free_hook(s, slab, p + i, 1);
+ alloc_tagging_slab_free_hook(s, slab, p + i, 1);
+
+ if (unlikely(!slab_free_hook(s, p[i], init, false))) {
+ p[i] = p[--sheaf->size];
+ continue;
+ }
+
+ i++;
+ }
+}
+
+static void rcu_free_sheaf(struct rcu_head *head)
+{
+ struct slab_sheaf *sheaf;
+ struct node_barn *barn;
+ struct kmem_cache *s;
+
+ sheaf = container_of(head, struct slab_sheaf, rcu_head);
+
+ s = sheaf->cache;
+
+ __rcu_free_sheaf_prepare(s, sheaf);
+
+ barn = get_node(s, numa_mem_id())->barn;
+
+ /* due to slab_free_hook() */
+ if (unlikely(sheaf->size == 0))
+ goto empty;
+
+ if (!barn_put_full_sheaf(barn, sheaf, false))
+ return;
+
+ sheaf_flush(s, sheaf);
+
+empty:
+ if (!barn_put_empty_sheaf(barn, sheaf, false))
+ return;
+
+ free_empty_sheaf(s, sheaf);
+}
+
+bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj)
+{
+ struct slub_percpu_sheaves *pcs;
+ struct slab_sheaf *rcu_sheaf;
+ unsigned long flags;
+
+ local_lock_irqsave(&s->cpu_sheaves->lock, flags);
+ pcs = this_cpu_ptr(s->cpu_sheaves);
+
+ if (unlikely(!pcs->rcu_free)) {
+
+ struct slab_sheaf *empty;
+
+ empty = barn_get_empty_sheaf(pcs->barn);
+
+ if (empty) {
+ pcs->rcu_free = empty;
+ goto do_free;
+ }
+
+ local_unlock_irqrestore(&s->cpu_sheaves->lock, flags);
+
+ empty = alloc_empty_sheaf(s, GFP_NOWAIT);
+
+ if (!empty) {
+ stat(s, FREE_RCU_SHEAF_FAIL);
+ return false;
+ }
+
+ local_lock_irqsave(&s->cpu_sheaves->lock, flags);
+ pcs = this_cpu_ptr(s->cpu_sheaves);
+
+ if (unlikely(pcs->rcu_free))
+ barn_put_empty_sheaf(pcs->barn, empty, true);
+ else
+ pcs->rcu_free = empty;
+ }
+
+do_free:
+
+ rcu_sheaf = pcs->rcu_free;
+
+ rcu_sheaf->objects[rcu_sheaf->size++] = obj;
+
+ if (likely(rcu_sheaf->size < s->sheaf_capacity)) {
+ local_unlock_irqrestore(&s->cpu_sheaves->lock, flags);
+ stat(s, FREE_RCU_SHEAF);
+ return true;
+ }
+
+ pcs->rcu_free = NULL;
+ local_unlock_irqrestore(&s->cpu_sheaves->lock, flags);
+
+ call_rcu(&rcu_sheaf->rcu_head, rcu_free_sheaf);
+
+ stat(s, FREE_RCU_SHEAF);
+
+ return true;
+}
+
/*
* Bulk free objects to the percpu sheaves.
* Unlike free_to_pcs() this includes the calls to all necessary hooks
@@ -6522,6 +6656,11 @@ int __kmem_cache_shutdown(struct kmem_cache *s)
struct kmem_cache_node *n;
flush_all_cpus_locked(s);
+
+ /* we might have rcu sheaves in flight */
+ if (s->cpu_sheaves)
+ rcu_barrier();
+
/* Attempt to free all objects */
for_each_kmem_cache_node(s, node, n) {
if (n->barn)
@@ -7927,6 +8066,8 @@ STAT_ATTR(ALLOC_PCS, alloc_cpu_sheaf);
STAT_ATTR(ALLOC_FASTPATH, alloc_fastpath);
STAT_ATTR(ALLOC_SLOWPATH, alloc_slowpath);
STAT_ATTR(FREE_PCS, free_cpu_sheaf);
+STAT_ATTR(FREE_RCU_SHEAF, free_rcu_sheaf);
+STAT_ATTR(FREE_RCU_SHEAF_FAIL, free_rcu_sheaf_fail);
STAT_ATTR(FREE_FASTPATH, free_fastpath);
STAT_ATTR(FREE_SLOWPATH, free_slowpath);
STAT_ATTR(FREE_FROZEN, free_frozen);
@@ -8022,6 +8163,8 @@ static struct attribute *slab_attrs[] = {
&alloc_fastpath_attr.attr,
&alloc_slowpath_attr.attr,
&free_cpu_sheaf_attr.attr,
+ &free_rcu_sheaf_attr.attr,
+ &free_rcu_sheaf_fail_attr.attr,
&free_fastpath_attr.attr,
&free_slowpath_attr.attr,
&free_frozen_attr.attr,
--
2.48.1
