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kvfree_rcu: Directly allocate page for single-argument case 

Single-argument kvfree_rcu() must be invoked from sleepable contexts,
so we can directly allocate pages.  Furthermmore, the fallback in case
of page-allocation failure is the high-latency synchronize_rcu(), so it
makes sense to do these page allocations from the fastpath, and even to
permit limited sleeping within the allocator.

This commit therefore allocates if needed on the fastpath using
GFP_KERNEL|__GFP_RETRY_MAYFAIL.  This also has the beneficial effect
of leaving kvfree_rcu()'s per-CPU caches to the double-argument variant
of kvfree_rcu(), given that the double-argument variant cannot directly
invoke the allocator.

[ paulmck: Add add_ptr_to_bulk_krc_lock header comment per Michal Hocko. ]
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Uladzislau Rezki (Sony) 2021-01-20 17:21:46 +01:00 committed by Paul E. McKenney
parent a38fd87484
commit 148e3731d1
1 changed files with 26 additions and 16 deletions
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42
kernel/rcu/tree.c
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@ -3493,37 +3493,50 @@ run_page_cache_worker(struct kfree_rcu_cpu *krcp)
}
}
// Record ptr in a page managed by krcp, with the pre-krc_this_cpu_lock()
// state specified by flags. If can_alloc is true, the caller must
// be schedulable and not be holding any locks or mutexes that might be
// acquired by the memory allocator or anything that it might invoke.
// Returns true if ptr was successfully recorded, else the caller must
// use a fallback.
static inline bool
kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr)
add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
unsigned long *flags, void *ptr, bool can_alloc)
{
struct kvfree_rcu_bulk_data *bnode;
int idx;
if (unlikely(!krcp->initialized))
*krcp = krc_this_cpu_lock(flags);
if (unlikely(!(*krcp)->initialized))
return false;
lockdep_assert_held(&krcp->lock);
idx = !!is_vmalloc_addr(ptr);
/* Check if a new block is required. */
if (!krcp->bkvhead[idx] ||
krcp->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) {
bnode = get_cached_bnode(krcp);
/* Switch to emergency path. */
if (!(*krcp)->bkvhead[idx] ||
(*krcp)->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) {
bnode = get_cached_bnode(*krcp);
if (!bnode && can_alloc) {
krc_this_cpu_unlock(*krcp, *flags);
bnode = (struct kvfree_rcu_bulk_data *)
__get_free_page(GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
*krcp = krc_this_cpu_lock(flags);
}
if (!bnode)
return false;
/* Initialize the new block. */
bnode->nr_records = 0;
bnode->next = krcp->bkvhead[idx];
bnode->next = (*krcp)->bkvhead[idx];
/* Attach it to the head. */
krcp->bkvhead[idx] = bnode;
(*krcp)->bkvhead[idx] = bnode;
}
/* Finally insert. */
krcp->bkvhead[idx]->records
[krcp->bkvhead[idx]->nr_records++] = ptr;
(*krcp)->bkvhead[idx]->records
[(*krcp)->bkvhead[idx]->nr_records++] = ptr;
return true;
}
@ -3561,8 +3574,6 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
ptr = (unsigned long *) func;
}
krcp = krc_this_cpu_lock(&flags);
// Queue the object but don't yet schedule the batch.
if (debug_rcu_head_queue(ptr)) {
// Probable double kfree_rcu(), just leak.
@ -3570,12 +3581,11 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
__func__, head);
// Mark as success and leave.
success = true;
goto unlock_return;
return;
}
kasan_record_aux_stack(ptr);
success = kvfree_call_rcu_add_ptr_to_bulk(krcp, ptr);
success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head);
if (!success) {
run_page_cache_worker(krcp);