From: Alexei Starovoitov <ast@xxxxxxxxxx>
Introduce bpf_mem_[cache_]free_rcu() similar to kfree_rcu().
Unlike bpf_mem_[cache_]free() that links objects for immediate reuse into
per-cpu free list the _rcu() flavor waits for RCU grace period and then moves
objects into free_by_rcu_ttrace list where they are waiting for RCU
task trace grace period to be freed into slab.
The life cycle of objects:
alloc: dequeue free_llist
free: enqeueu free_llist
free_rcu: enqueue free_by_rcu -> waiting_for_gp
free_llist above high watermark -> free_by_rcu_ttrace
after RCU GP waiting_for_gp -> free_by_rcu_ttrace
free_by_rcu_ttrace -> waiting_for_gp_ttrace -> slab
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
include/linux/bpf_mem_alloc.h | 2 +
kernel/bpf/memalloc.c | 118 ++++++++++++++++++++++++++++++++--
2 files changed, 116 insertions(+), 4 deletions(-)
diff --git a/include/linux/bpf_mem_alloc.h b/include/linux/bpf_mem_alloc.h
index 3929be5743f4..d644bbb298af 100644
--- a/include/linux/bpf_mem_alloc.h
+++ b/include/linux/bpf_mem_alloc.h
@@ -27,10 +27,12 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma);
/* kmalloc/kfree equivalent: */
void *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size);
void bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr);
+void bpf_mem_free_rcu(struct bpf_mem_alloc *ma, void *ptr);
/* kmem_cache_alloc/free equivalent: */
void *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma);
void bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr);
+void bpf_mem_cache_free_rcu(struct bpf_mem_alloc *ma, void *ptr);
void bpf_mem_cache_raw_free(void *ptr);
void *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags);
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 10d027674743..4d1002e7b4b5 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -100,6 +100,15 @@ struct bpf_mem_cache {
int percpu_size;
struct bpf_mem_cache *tgt;
+ /* list of objects to be freed after RCU GP */
+ struct llist_head free_by_rcu;
+ struct llist_node *free_by_rcu_tail;
+ struct llist_head waiting_for_gp;
+ struct llist_node *waiting_for_gp_tail;
+ struct rcu_head rcu;
+ atomic_t call_rcu_in_progress;
+ struct llist_head free_llist_extra_rcu;
+
/* list of objects to be freed after RCU tasks trace GP */
struct llist_head free_by_rcu_ttrace;
struct llist_node *free_by_rcu_ttrace_tail;
@@ -340,6 +349,56 @@ static void free_bulk(struct bpf_mem_cache *c)
do_call_rcu_ttrace(tgt);
}
+static void __free_by_rcu(struct rcu_head *head)
+{
+ struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
+ struct bpf_mem_cache *tgt = c->tgt;
+ struct llist_node *llnode = llist_del_all(&c->waiting_for_gp);
+
+ if (!llnode)
+ goto out;
+
+ if (llist_add_batch(llnode, c->waiting_for_gp_tail, &tgt->free_by_rcu_ttrace))
+ tgt->free_by_rcu_ttrace_tail = c->waiting_for_gp_tail;
+
+ /* Objects went through regular RCU GP. Send them to RCU tasks trace */
+ do_call_rcu_ttrace(tgt);
+out:
+ atomic_set(&c->call_rcu_in_progress, 0);
+}
+
+static void check_free_by_rcu(struct bpf_mem_cache *c)
+{
+ struct llist_node *llnode, *t;
+
+ if (llist_empty(&c->free_by_rcu) && llist_empty(&c->free_llist_extra_rcu))
+ return;
+
+ /* drain free_llist_extra_rcu */
+ llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra_rcu))
+ if (__llist_add(llnode, &c->free_by_rcu))
+ c->free_by_rcu_tail = llnode;
+
+ if (atomic_xchg(&c->call_rcu_in_progress, 1)) {
+ /*
+ * Instead of kmalloc-ing new rcu_head and triggering 10k
+ * call_rcu() to hit rcutree.qhimark and force RCU to notice
+ * the overload just ask RCU to hurry up. There could be many
+ * objects in free_by_rcu list.
+ * This hint reduces memory consumption for an artifical
+ * benchmark from 2 Gbyte to 150 Mbyte.
+ */
+ rcu_request_urgent_qs_task(current);
+ return;
+ }
+
+ WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));
+
+ WRITE_ONCE(c->waiting_for_gp.first, __llist_del_all(&c->free_by_rcu));
+ c->waiting_for_gp_tail = c->free_by_rcu_tail;
+ call_rcu_hurry(&c->rcu, __free_by_rcu);
+}
+
static void bpf_mem_refill(struct irq_work *work)
{
struct bpf_mem_cache *c = container_of(work, struct bpf_mem_cache, refill_work);
@@ -354,6 +413,8 @@ static void bpf_mem_refill(struct irq_work *work)
alloc_bulk(c, c->batch, NUMA_NO_NODE);
else if (cnt > c->high_watermark)
free_bulk(c);
+
+ check_free_by_rcu(c);
}
static void notrace irq_work_raise(struct bpf_mem_cache *c)
@@ -482,6 +543,9 @@ static void drain_mem_cache(struct bpf_mem_cache *c)
free_all(llist_del_all(&c->waiting_for_gp_ttrace), percpu);
free_all(__llist_del_all(&c->free_llist), percpu);
free_all(__llist_del_all(&c->free_llist_extra), percpu);
+ free_all(__llist_del_all(&c->free_by_rcu), percpu);
+ free_all(__llist_del_all(&c->free_llist_extra_rcu), percpu);
+ free_all(llist_del_all(&c->waiting_for_gp), percpu);
}
static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
@@ -494,8 +558,8 @@ static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
static void free_mem_alloc(struct bpf_mem_alloc *ma)
{
- /* waiting_for_gp_ttrace lists was drained, but __free_rcu might
- * still execute. Wait for it now before we freeing percpu caches.
+ /* waiting_for_gp[_ttrace] lists were drained, but RCU callbacks
+ * might still execute. Wait for them.
*
* rcu_barrier_tasks_trace() doesn't imply synchronize_rcu_tasks_trace(),
* but rcu_barrier_tasks_trace() and rcu_barrier() below are only used
@@ -504,9 +568,10 @@ static void free_mem_alloc(struct bpf_mem_alloc *ma)
* rcu_trace_implies_rcu_gp(), it will be OK to skip rcu_barrier() by
* using rcu_trace_implies_rcu_gp() as well.
*/
- rcu_barrier_tasks_trace();
+ rcu_barrier(); /* wait for __free_by_rcu() */
+ rcu_barrier_tasks_trace(); /* wait for __free_rcu() via call_rcu_tasks_trace */
if (!rcu_trace_implies_rcu_gp())
- rcu_barrier();
+ rcu_barrier(); /* wait for __free_rcu() via call_rcu */
free_mem_alloc_no_barrier(ma);
}
@@ -565,6 +630,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
irq_work_sync(&c->refill_work);
drain_mem_cache(c);
rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);
+ rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
}
/* objcg is the same across cpus */
if (c->objcg)
@@ -580,6 +646,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
irq_work_sync(&c->refill_work);
drain_mem_cache(c);
rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);
+ rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
}
}
if (c->objcg)
@@ -664,6 +731,27 @@ static void notrace unit_free(struct bpf_mem_cache *c, void *ptr)
irq_work_raise(c);
}
+static void notrace unit_free_rcu(struct bpf_mem_cache *c, void *ptr)
+{
+ struct llist_node *llnode = ptr - LLIST_NODE_SZ;
+ unsigned long flags;
+
+ c->tgt = *(struct bpf_mem_cache **)llnode;
+
+ local_irq_save(flags);
+ if (local_inc_return(&c->active) == 1) {
+ if (__llist_add(llnode, &c->free_by_rcu))
+ c->free_by_rcu_tail = llnode;
+ } else {
+ llist_add(llnode, &c->free_llist_extra_rcu);
+ }
+ local_dec(&c->active);
+ local_irq_restore(flags);
+
+ if (!atomic_read(&c->call_rcu_in_progress))
+ irq_work_raise(c);
+}
+
/* Called from BPF program or from sys_bpf syscall.
* In both cases migration is disabled.
*/
@@ -697,6 +785,20 @@ void notrace bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr)
unit_free(this_cpu_ptr(ma->caches)->cache + idx, ptr);
}
+void notrace bpf_mem_free_rcu(struct bpf_mem_alloc *ma, void *ptr)
+{
+ int idx;
+
+ if (!ptr)
+ return;
+
+ idx = bpf_mem_cache_idx(ksize(ptr - LLIST_NODE_SZ));
+ if (idx < 0)
+ return;
+
+ unit_free_rcu(this_cpu_ptr(ma->caches)->cache + idx, ptr);
+}
+
void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma)
{
void *ret;
@@ -713,6 +815,14 @@ void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)
unit_free(this_cpu_ptr(ma->cache), ptr);
}
+void notrace bpf_mem_cache_free_rcu(struct bpf_mem_alloc *ma, void *ptr)
+{
+ if (!ptr)
+ return;
+
+ unit_free_rcu(this_cpu_ptr(ma->cache), ptr);
+}
+
/* Directly does a kfree() without putting 'ptr' back to the free_llist
* for reuse and without waiting for a rcu_tasks_trace gp.
* The caller must first go through the rcu_tasks_trace gp for 'ptr'
--
2.34.1
