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) <ure...@gmail.com> --- 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