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* [PATCH 1/3] kvfree_rcu: Allocate a page for a single argument
@ 2021-01-20 16:21 Uladzislau Rezki (Sony)
  2021-01-20 16:21 ` [PATCH 2/3] kvfree_rcu: Use __GFP_NOMEMALLOC for single-argument kvfree_rcu() Uladzislau Rezki (Sony)
                   ` (4 more replies)
  0 siblings, 5 replies; 36+ messages in thread
From: Uladzislau Rezki (Sony) @ 2021-01-20 16:21 UTC (permalink / raw)
  To: LKML, RCU, Paul E . McKenney, Michael Ellerman
  Cc: Andrew Morton, Daniel Axtens, Frederic Weisbecker,
	Neeraj Upadhyay, Joel Fernandes, Peter Zijlstra, Michal Hocko,
	Thomas Gleixner, Theodore Y . Ts'o,
	Sebastian Andrzej Siewior, Uladzislau Rezki, Oleksiy Avramchenko

For a single argument we can directly request a page from a caller
context when a "carry page block" is run out of free spots. Instead
of hitting a slow path we can request an extra page by demand and
proceed with a fast path.

A single-argument kvfree_rcu() must be invoked in sleepable contexts,
and that its fallback is the relatively high latency synchronize_rcu().
Single-argument kvfree_rcu() therefore uses GFP_KERNEL|__GFP_RETRY_MAYFAIL
to allow limited sleeping within the memory 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>
---
 kernel/rcu/tree.c | 42 ++++++++++++++++++++++++++----------------
 1 file changed, 26 insertions(+), 16 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e04e336bee42..2014fb22644d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3465,37 +3465,50 @@ 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;
 }
@@ -3533,8 +3546,6 @@ 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.
@@ -3542,12 +3553,11 @@ 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);
 
-- 
2.20.1


^ permalink raw reply related	[flat|nested] 36+ messages in thread

end of thread, other threads:[~2021-02-03 19:38 UTC | newest]

Thread overview: 36+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-01-20 16:21 [PATCH 1/3] kvfree_rcu: Allocate a page for a single argument Uladzislau Rezki (Sony)
2021-01-20 16:21 ` [PATCH 2/3] kvfree_rcu: Use __GFP_NOMEMALLOC for single-argument kvfree_rcu() Uladzislau Rezki (Sony)
2021-01-28 18:06   ` Uladzislau Rezki
2021-01-20 16:21 ` [PATCH 3/3] kvfree_rcu: use migrate_disable/enable() Uladzislau Rezki (Sony)
2021-01-20 19:45   ` Sebastian Andrzej Siewior
2021-01-20 21:42     ` Paul E. McKenney
2021-01-23  9:31   ` 回复: " Zhang, Qiang
2021-01-24 21:57     ` Uladzislau Rezki
2021-01-25  1:50       ` 回复: " Zhang, Qiang
2021-01-25  2:18         ` Zhang, Qiang
2021-01-25 13:49           ` Uladzislau Rezki
2021-01-26  9:33             ` 回复: " Zhang, Qiang
2021-01-26 13:43               ` Uladzislau Rezki
2021-01-20 18:40 ` [PATCH 1/3] kvfree_rcu: Allocate a page for a single argument Paul E. McKenney
2021-01-20 19:57 ` Sebastian Andrzej Siewior
2021-01-20 21:54   ` Paul E. McKenney
2021-01-21 13:35     ` Uladzislau Rezki
2021-01-21 15:07       ` Paul E. McKenney
2021-01-21 19:17         ` Uladzislau Rezki
2021-01-22 11:17     ` Sebastian Andrzej Siewior
2021-01-22 15:28       ` Paul E. McKenney
2021-01-21 12:38   ` Uladzislau Rezki
2021-01-22 11:34     ` Sebastian Andrzej Siewior
2021-01-22 14:21       ` Uladzislau Rezki
2021-01-25 13:22 ` Michal Hocko
2021-01-25 14:31   ` Uladzislau Rezki
2021-01-25 15:39     ` Michal Hocko
2021-01-25 16:25       ` Uladzislau Rezki
2021-01-28 15:11         ` Uladzislau Rezki
2021-01-28 15:17           ` Michal Hocko
2021-01-28 15:30             ` Uladzislau Rezki
2021-01-28 18:02               ` Uladzislau Rezki
     [not found]                 ` <YBPNvbJLg56XU8co@dhcp22.suse.cz>
2021-01-29 16:35                   ` Uladzislau Rezki
2021-02-01 11:47                     ` Michal Hocko
2021-02-01 14:44                       ` Uladzislau Rezki
2021-02-03 19:37                       ` Paul E. McKenney

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