Add a support of dynamically attaching an rcu_head to an object
which gets freed via the single argument of kvfree_rcu(). This is
used in the path, when a page allocation fails due to a high memory
pressure.
The basic idea behind of this is to minimize a hit of slow path
which requires a caller to wait until a grace period is passed.
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
---
kernel/rcu/tree.c | 53 +++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 49 insertions(+), 4 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index be00aac5f4e7..0124411fecfb 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3425,6 +3425,11 @@ kvfree_rcu_bulk(struct kfree_rcu_cpu *krcp,
cond_resched_tasks_rcu_qs();
}
+struct dyn_rcu_head {
+ unsigned long *ptr;
+ struct rcu_head rh;
+};
+
static void
kvfree_rcu_list(struct rcu_head *head)
{
@@ -3433,15 +3438,32 @@ kvfree_rcu_list(struct rcu_head *head)
for (; head; head = next) {
void *ptr = (void *) head->func;
unsigned long offset = (void *) head - ptr;
+ struct dyn_rcu_head *drhp = NULL;
+
+ /*
+ * For dynamically attached rcu_head, a ->func field
+ * points to _offset_, i.e. not to a pointer which has
+ * to be freed. For such objects, adjust an offset and
+ * pointer.
+ */
+ if (__is_kvfree_rcu_offset((unsigned long) ptr)) {
+ drhp = container_of(head, struct dyn_rcu_head, rh);
+ offset = (unsigned long) drhp->rh.func;
+ ptr = drhp->ptr;
+ }
next = head->next;
debug_rcu_head_unqueue((struct rcu_head *)ptr);
rcu_lock_acquire(&rcu_callback_map);
trace_rcu_invoke_kvfree_callback(rcu_state.name, head, offset);
- if (!WARN_ON_ONCE(!__is_kvfree_rcu_offset(offset)))
+ if (!WARN_ON_ONCE(!__is_kvfree_rcu_offset(offset))) {
kvfree(ptr);
+ if (drhp)
+ kvfree(drhp);
+ }
+
rcu_lock_release(&rcu_callback_map);
cond_resched_tasks_rcu_qs();
}
@@ -3787,6 +3809,21 @@ add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
return true;
}
+static struct rcu_head *
+attach_rcu_head_to_object(void *obj)
+{
+ struct dyn_rcu_head *rhp;
+
+ rhp = kmalloc(sizeof(struct dyn_rcu_head), GFP_KERNEL |
+ __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+
+ if (!rhp)
+ return NULL;
+
+ rhp->ptr = obj;
+ return &rhp->rh;
+}
+
/*
* Queue a request for lazy invocation of the appropriate free routine
* after a grace period. Please note that three paths are maintained,
@@ -3830,9 +3867,17 @@ void kvfree_call_rcu(struct rcu_head *head, void *ptr)
if (!success) {
run_page_cache_worker(krcp);
- if (head == NULL)
- // Inline if kvfree_rcu(one_arg) call.
- goto unlock_return;
+ if (!head) {
+ krc_this_cpu_unlock(krcp, flags);
+ head = attach_rcu_head_to_object(ptr);
+ krcp = krc_this_cpu_lock(&flags);
+
+ if (!head)
+ // Inline if kvfree_rcu(one_arg) call.
+ goto unlock_return;
+
+ ptr = (rcu_callback_t) offsetof(struct dyn_rcu_head, rh);
+ }
head->func = ptr;
head->next = krcp->head;
--
2.39.2
