[PATCH net-next v9 0/6] Improve neigh_flush_dev performance

[PATCH net-next v9 0/6] Improve neigh_flush_dev performance

[Gilad Naaman]

This patchsets improves the performance of neigh_flush_dev.

Currently, the only way to implement it requires traversing
all neighbours known to the kernel, across all network-namespaces.

This means that some flows are slowed down as a function of neigh-scale,
even if the specific link they're handling has little to no neighbours.

In order to solve this, this patchset adds a netdev->neighbours list,
as well as making the original linked-list doubly-, so that it is
possible to unlink neighbours without traversing the hash-bucket to
obtain the previous neighbour.

The original use-case we encountered was mass-deletion of links (12K
VLANs) while there are 50K ARPs and 50K NDPs in the system; though the
slowdowns would also appear when the links are set down.

Changes in v9:
 - Use RCU iteration in ___neigh_lookup_noref and neigh_dump_table

I kept the reviewed-by tags, as instructed, but note that there are
minor changes in commits 2/6 and 4/6 (just adding the `_rcu`).

Gilad Naaman (6):
  neighbour: Add hlist_node to struct neighbour
  neighbour: Define neigh_for_each_in_bucket
  neighbour: Convert seq_file functions to use hlist
  neighbour: Convert iteration to use hlist+macro
  neighbour: Remove bare neighbour::next pointer
  neighbour: Create netdev->neighbour association

 .../networking/net_cachelines/net_device.rst  |   1 +
 include/linux/netdevice.h                     |   7 +
 include/net/neighbour.h                       |  26 +-
 include/net/neighbour_tables.h                |  12 +
 net/core/neighbour.c                          | 325 ++++++++----------
 net/ipv4/arp.c                                |   2 +-
 6 files changed, 170 insertions(+), 203 deletions(-)
 create mode 100644 include/net/neighbour_tables.h

-- 
2.34.1

[PATCH net-next v9 1/6] neighbour: Add hlist_node to struct neighbour

[Gilad Naaman]

Add a doubly-linked node to neighbours, so that they
can be deleted without iterating the entire bucket they're in.

Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 include/net/neighbour.h |  2 ++
 net/core/neighbour.c    | 20 +++++++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 3887ed9e5026..0402447854c7 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -136,6 +136,7 @@ struct neigh_statistics {
 
 struct neighbour {
 	struct neighbour __rcu	*next;
+	struct hlist_node	hash;
 	struct neigh_table	*tbl;
 	struct neigh_parms	*parms;
 	unsigned long		confirmed;
@@ -191,6 +192,7 @@ struct pneigh_entry {
 
 struct neigh_hash_table {
 	struct neighbour __rcu	**hash_buckets;
+	struct hlist_head	*hash_heads;
 	unsigned int		hash_shift;
 	__u32			hash_rnd[NEIGH_NUM_HASH_RND];
 	struct rcu_head		rcu;
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 4b871cecd2ce..5552e6b05c82 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -216,6 +216,7 @@ static bool neigh_del(struct neighbour *n, struct neighbour __rcu **np,
 		neigh = rcu_dereference_protected(n->next,
 						  lockdep_is_held(&tbl->lock));
 		rcu_assign_pointer(*np, neigh);
+		hlist_del_rcu(&n->hash);
 		neigh_mark_dead(n);
 		retval = true;
 	}
@@ -402,6 +403,7 @@ static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev,
 			rcu_assign_pointer(*np,
 				   rcu_dereference_protected(n->next,
 						lockdep_is_held(&tbl->lock)));
+			hlist_del_rcu(&n->hash);
 			write_lock(&n->lock);
 			neigh_del_timer(n);
 			neigh_mark_dead(n);
@@ -529,20 +531,30 @@ static void neigh_get_hash_rnd(u32 *x)
 
 static struct neigh_hash_table *neigh_hash_alloc(unsigned int shift)
 {
+	size_t hash_heads_size = (1 << shift) * sizeof(struct hlist_head);
 	size_t size = (1 << shift) * sizeof(struct neighbour *);
-	struct neigh_hash_table *ret;
 	struct neighbour __rcu **buckets;
+	struct hlist_head *hash_heads;
+	struct neigh_hash_table *ret;
 	int i;
 
 	ret = kmalloc(sizeof(*ret), GFP_ATOMIC);
 	if (!ret)
 		return NULL;
+
 	buckets = kvzalloc(size, GFP_ATOMIC);
 	if (!buckets) {
 		kfree(ret);
 		return NULL;
 	}
+	hash_heads = kvzalloc(hash_heads_size, GFP_ATOMIC);
+	if (!hash_heads) {
+		kvfree(buckets);
+		kfree(ret);
+		return NULL;
+	}
 	ret->hash_buckets = buckets;
+	ret->hash_heads = hash_heads;
 	ret->hash_shift = shift;
 	for (i = 0; i < NEIGH_NUM_HASH_RND; i++)
 		neigh_get_hash_rnd(&ret->hash_rnd[i]);
@@ -556,6 +568,7 @@ static void neigh_hash_free_rcu(struct rcu_head *head)
 						    rcu);
 
 	kvfree(nht->hash_buckets);
+	kvfree(nht->hash_heads);
 	kfree(nht);
 }
 
@@ -592,6 +605,8 @@ static struct neigh_hash_table *neigh_hash_grow(struct neigh_table *tbl,
 						new_nht->hash_buckets[hash],
 						lockdep_is_held(&tbl->lock)));
 			rcu_assign_pointer(new_nht->hash_buckets[hash], n);
+			hlist_del_rcu(&n->hash);
+			hlist_add_head_rcu(&n->hash, &new_nht->hash_heads[hash]);
 		}
 	}
 
@@ -702,6 +717,7 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
 			   rcu_dereference_protected(nht->hash_buckets[hash_val],
 						     lockdep_is_held(&tbl->lock)));
 	rcu_assign_pointer(nht->hash_buckets[hash_val], n);
+	hlist_add_head_rcu(&n->hash, &nht->hash_heads[hash_val]);
 	write_unlock_bh(&tbl->lock);
 	neigh_dbg(2, "neigh %p is created\n", n);
 	rc = n;
@@ -987,6 +1003,7 @@ static void neigh_periodic_work(struct work_struct *work)
 				rcu_assign_pointer(*np,
 					rcu_dereference_protected(n->next,
 						lockdep_is_held(&tbl->lock)));
+				hlist_del_rcu(&n->hash);
 				neigh_mark_dead(n);
 				write_unlock(&n->lock);
 				neigh_cleanup_and_release(n);
@@ -3116,6 +3133,7 @@ void __neigh_for_each_release(struct neigh_table *tbl,
 				rcu_assign_pointer(*np,
 					rcu_dereference_protected(n->next,
 						lockdep_is_held(&tbl->lock)));
+				hlist_del_rcu(&n->hash);
 				neigh_mark_dead(n);
 			} else
 				np = &n->next;
-- 
2.34.1

Re: [PATCH net-next v9 1/6] neighbour: Add hlist_node to struct neighbour

[Eric Dumazet]

On Thu, Nov 7, 2024 at 5:05 PM Gilad Naaman <gnaaman@drivenets.com> wrote:
>
> Add a doubly-linked node to neighbours, so that they
> can be deleted without iterating the entire bucket they're in.
>
> Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
> Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---
>  include/net/neighbour.h |  2 ++
>  net/core/neighbour.c    | 20 +++++++++++++++++++-
>  2 files changed, 21 insertions(+), 1 deletion(-)

Reviewed-by: Eric Dumazet <edumazet@google.com>

[PATCH net-next v9 2/6] neighbour: Define neigh_for_each_in_bucket

[Gilad Naaman]

Introduce neigh_for_each_in_bucket in neighbour.h, to help iterate over
the neighbour table more succinctly.

Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 include/net/neighbour.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 0402447854c7..4b9068c5e668 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -277,6 +277,12 @@ static inline void *neighbour_priv(const struct neighbour *n)
 
 extern const struct nla_policy nda_policy[];
 
+#define neigh_for_each_in_bucket(pos, head) hlist_for_each_entry(pos, head, hash)
+#define neigh_for_each_in_bucket_rcu(pos, head) \
+	hlist_for_each_entry_rcu(pos, head, hash)
+#define neigh_for_each_in_bucket_safe(pos, tmp, head) \
+	hlist_for_each_entry_safe(pos, tmp, head, hash)
+
 static inline bool neigh_key_eq32(const struct neighbour *n, const void *pkey)
 {
 	return *(const u32 *)n->primary_key == *(const u32 *)pkey;
-- 
2.34.1

Re: [PATCH net-next v9 2/6] neighbour: Define neigh_for_each_in_bucket

[Eric Dumazet]

On Thu, Nov 7, 2024 at 5:05 PM Gilad Naaman <gnaaman@drivenets.com> wrote:
>
> Introduce neigh_for_each_in_bucket in neighbour.h, to help iterate over
> the neighbour table more succinctly.
>
> Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
> Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Reviewed-by: Eric Dumazet <edumazet@google.com>

[PATCH net-next v9 3/6] neighbour: Convert seq_file functions to use hlist

[Gilad Naaman]

Convert seq_file-related neighbour functionality to use neighbour::hash
and the related for_each macro.

Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 net/core/neighbour.c | 104 ++++++++++++++++++++-----------------------
 1 file changed, 48 insertions(+), 56 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 5552e6b05c82..3485d6b3ba99 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -3193,43 +3193,53 @@ EXPORT_SYMBOL(neigh_xmit);
 
 #ifdef CONFIG_PROC_FS
 
-static struct neighbour *neigh_get_first(struct seq_file *seq)
+static struct neighbour *neigh_get_valid(struct seq_file *seq,
+					 struct neighbour *n,
+					 loff_t *pos)
 {
 	struct neigh_seq_state *state = seq->private;
 	struct net *net = seq_file_net(seq);
+
+	if (!net_eq(dev_net(n->dev), net))
+		return NULL;
+
+	if (state->neigh_sub_iter) {
+		loff_t fakep = 0;
+		void *v;
+
+		v = state->neigh_sub_iter(state, n, pos ? pos : &fakep);
+		if (!v)
+			return NULL;
+		if (pos)
+			return v;
+	}
+
+	if (!(state->flags & NEIGH_SEQ_SKIP_NOARP))
+		return n;
+
+	if (READ_ONCE(n->nud_state) & ~NUD_NOARP)
+		return n;
+
+	return NULL;
+}
+
+static struct neighbour *neigh_get_first(struct seq_file *seq)
+{
+	struct neigh_seq_state *state = seq->private;
 	struct neigh_hash_table *nht = state->nht;
-	struct neighbour *n = NULL;
-	int bucket;
+	struct neighbour *n, *tmp;
 
 	state->flags &= ~NEIGH_SEQ_IS_PNEIGH;
-	for (bucket = 0; bucket < (1 << nht->hash_shift); bucket++) {
-		n = rcu_dereference(nht->hash_buckets[bucket]);
-
-		while (n) {
-			if (!net_eq(dev_net(n->dev), net))
-				goto next;
-			if (state->neigh_sub_iter) {
-				loff_t fakep = 0;
-				void *v;
 
-				v = state->neigh_sub_iter(state, n, &fakep);
-				if (!v)
-					goto next;
-			}
-			if (!(state->flags & NEIGH_SEQ_SKIP_NOARP))
-				break;
-			if (READ_ONCE(n->nud_state) & ~NUD_NOARP)
-				break;
-next:
-			n = rcu_dereference(n->next);
+	while (++state->bucket < (1 << nht->hash_shift)) {
+		neigh_for_each_in_bucket(n, &nht->hash_heads[state->bucket]) {
+			tmp = neigh_get_valid(seq, n, NULL);
+			if (tmp)
+				return tmp;
 		}
-
-		if (n)
-			break;
 	}
-	state->bucket = bucket;
 
-	return n;
+	return NULL;
 }
 
 static struct neighbour *neigh_get_next(struct seq_file *seq,
@@ -3237,46 +3247,28 @@ static struct neighbour *neigh_get_next(struct seq_file *seq,
 					loff_t *pos)
 {
 	struct neigh_seq_state *state = seq->private;
-	struct net *net = seq_file_net(seq);
-	struct neigh_hash_table *nht = state->nht;
+	struct neighbour *tmp;
 
 	if (state->neigh_sub_iter) {
 		void *v = state->neigh_sub_iter(state, n, pos);
+
 		if (v)
 			return n;
 	}
-	n = rcu_dereference(n->next);
-
-	while (1) {
-		while (n) {
-			if (!net_eq(dev_net(n->dev), net))
-				goto next;
-			if (state->neigh_sub_iter) {
-				void *v = state->neigh_sub_iter(state, n, pos);
-				if (v)
-					return n;
-				goto next;
-			}
-			if (!(state->flags & NEIGH_SEQ_SKIP_NOARP))
-				break;
 
-			if (READ_ONCE(n->nud_state) & ~NUD_NOARP)
-				break;
-next:
-			n = rcu_dereference(n->next);
+	hlist_for_each_entry_continue(n, hash) {
+		tmp = neigh_get_valid(seq, n, pos);
+		if (tmp) {
+			n = tmp;
+			goto out;
 		}
-
-		if (n)
-			break;
-
-		if (++state->bucket >= (1 << nht->hash_shift))
-			break;
-
-		n = rcu_dereference(nht->hash_buckets[state->bucket]);
 	}
 
+	n = neigh_get_first(seq);
+out:
 	if (n && pos)
 		--(*pos);
+
 	return n;
 }
 
@@ -3379,7 +3371,7 @@ void *neigh_seq_start(struct seq_file *seq, loff_t *pos, struct neigh_table *tbl
 	struct neigh_seq_state *state = seq->private;
 
 	state->tbl = tbl;
-	state->bucket = 0;
+	state->bucket = -1;
 	state->flags = (neigh_seq_flags & ~NEIGH_SEQ_IS_PNEIGH);
 
 	rcu_read_lock();
-- 
2.34.1

Re: [PATCH net-next v9 3/6] neighbour: Convert seq_file functions to use hlist

[Eric Dumazet]

On Thu, Nov 7, 2024 at 5:05 PM Gilad Naaman <gnaaman@drivenets.com> wrote:
>
> Convert seq_file-related neighbour functionality to use neighbour::hash
> and the related for_each macro.
>
> Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
> Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---

Reviewed-by: Eric Dumazet <edumazet@google.com>

[PATCH net-next v9 4/6] neighbour: Convert iteration to use hlist+macro

[Gilad Naaman]

Remove all usage of the bare neighbour::next pointer,
replacing them with neighbour::hash and its for_each macro.

Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 include/net/neighbour.h |  5 +----
 net/core/neighbour.c    | 47 ++++++++++++++++-------------------------
 2 files changed, 19 insertions(+), 33 deletions(-)

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 4b9068c5e668..94cf4f8c118f 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -311,12 +311,9 @@ static inline struct neighbour *___neigh_lookup_noref(
 	u32 hash_val;
 
 	hash_val = hash(pkey, dev, nht->hash_rnd) >> (32 - nht->hash_shift);
-	for (n = rcu_dereference(nht->hash_buckets[hash_val]);
-	     n != NULL;
-	     n = rcu_dereference(n->next)) {
+	neigh_for_each_in_bucket_rcu(n, &nht->hash_heads[hash_val])
 		if (n->dev == dev && key_eq(n, pkey))
 			return n;
-	}
 
 	return NULL;
 }
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 3485d6b3ba99..f99354d768c2 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -387,11 +387,11 @@ static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev,
 					lockdep_is_held(&tbl->lock));
 
 	for (i = 0; i < (1 << nht->hash_shift); i++) {
-		struct neighbour *n;
 		struct neighbour __rcu **np = &nht->hash_buckets[i];
+		struct hlist_node *tmp;
+		struct neighbour *n;
 
-		while ((n = rcu_dereference_protected(*np,
-					lockdep_is_held(&tbl->lock))) != NULL) {
+		neigh_for_each_in_bucket_safe(n, tmp, &nht->hash_heads[i]) {
 			if (dev && n->dev != dev) {
 				np = &n->next;
 				continue;
@@ -587,18 +587,14 @@ static struct neigh_hash_table *neigh_hash_grow(struct neigh_table *tbl,
 		return old_nht;
 
 	for (i = 0; i < (1 << old_nht->hash_shift); i++) {
-		struct neighbour *n, *next;
+		struct hlist_node *tmp;
+		struct neighbour *n;
 
-		for (n = rcu_dereference_protected(old_nht->hash_buckets[i],
-						   lockdep_is_held(&tbl->lock));
-		     n != NULL;
-		     n = next) {
+		neigh_for_each_in_bucket_safe(n, tmp, &old_nht->hash_heads[i]) {
 			hash = tbl->hash(n->primary_key, n->dev,
 					 new_nht->hash_rnd);
 
 			hash >>= (32 - new_nht->hash_shift);
-			next = rcu_dereference_protected(n->next,
-						lockdep_is_held(&tbl->lock));
 
 			rcu_assign_pointer(n->next,
 					   rcu_dereference_protected(
@@ -693,11 +689,7 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
 		goto out_tbl_unlock;
 	}
 
-	for (n1 = rcu_dereference_protected(nht->hash_buckets[hash_val],
-					    lockdep_is_held(&tbl->lock));
-	     n1 != NULL;
-	     n1 = rcu_dereference_protected(n1->next,
-			lockdep_is_held(&tbl->lock))) {
+	neigh_for_each_in_bucket(n1, &nht->hash_heads[hash_val]) {
 		if (dev == n1->dev && !memcmp(n1->primary_key, n->primary_key, key_len)) {
 			if (want_ref)
 				neigh_hold(n1);
@@ -949,10 +941,11 @@ static void neigh_connect(struct neighbour *neigh)
 static void neigh_periodic_work(struct work_struct *work)
 {
 	struct neigh_table *tbl = container_of(work, struct neigh_table, gc_work.work);
-	struct neighbour *n;
+	struct neigh_hash_table *nht;
 	struct neighbour __rcu **np;
+	struct hlist_node *tmp;
+	struct neighbour *n;
 	unsigned int i;
-	struct neigh_hash_table *nht;
 
 	NEIGH_CACHE_STAT_INC(tbl, periodic_gc_runs);
 
@@ -979,8 +972,7 @@ static void neigh_periodic_work(struct work_struct *work)
 	for (i = 0 ; i < (1 << nht->hash_shift); i++) {
 		np = &nht->hash_buckets[i];
 
-		while ((n = rcu_dereference_protected(*np,
-				lockdep_is_held(&tbl->lock))) != NULL) {
+		neigh_for_each_in_bucket_safe(n, tmp, &nht->hash_heads[i]) {
 			unsigned int state;
 
 			write_lock(&n->lock);
@@ -2730,9 +2722,8 @@ static int neigh_dump_table(struct neigh_table *tbl, struct sk_buff *skb,
 	for (h = s_h; h < (1 << nht->hash_shift); h++) {
 		if (h > s_h)
 			s_idx = 0;
-		for (n = rcu_dereference(nht->hash_buckets[h]), idx = 0;
-		     n != NULL;
-		     n = rcu_dereference(n->next)) {
+		idx = 0;
+		neigh_for_each_in_bucket_rcu(n, &nht->hash_heads[h]) {
 			if (idx < s_idx || !net_eq(dev_net(n->dev), net))
 				goto next;
 			if (neigh_ifindex_filtered(n->dev, filter->dev_idx) ||
@@ -3099,9 +3090,7 @@ void neigh_for_each(struct neigh_table *tbl, void (*cb)(struct neighbour *, void
 	for (chain = 0; chain < (1 << nht->hash_shift); chain++) {
 		struct neighbour *n;
 
-		for (n = rcu_dereference(nht->hash_buckets[chain]);
-		     n != NULL;
-		     n = rcu_dereference(n->next))
+		neigh_for_each_in_bucket(n, &nht->hash_heads[chain])
 			cb(n, cookie);
 	}
 	read_unlock_bh(&tbl->lock);
@@ -3113,18 +3102,18 @@ EXPORT_SYMBOL(neigh_for_each);
 void __neigh_for_each_release(struct neigh_table *tbl,
 			      int (*cb)(struct neighbour *))
 {
-	int chain;
 	struct neigh_hash_table *nht;
+	int chain;
 
 	nht = rcu_dereference_protected(tbl->nht,
 					lockdep_is_held(&tbl->lock));
 	for (chain = 0; chain < (1 << nht->hash_shift); chain++) {
-		struct neighbour *n;
 		struct neighbour __rcu **np;
+		struct hlist_node *tmp;
+		struct neighbour *n;
 
 		np = &nht->hash_buckets[chain];
-		while ((n = rcu_dereference_protected(*np,
-					lockdep_is_held(&tbl->lock))) != NULL) {
+		neigh_for_each_in_bucket_safe(n, tmp, &nht->hash_heads[chain]) {
 			int release;
 
 			write_lock(&n->lock);
-- 
2.34.1

Re: [PATCH net-next v9 4/6] neighbour: Convert iteration to use hlist+macro

[Eric Dumazet]

On Thu, Nov 7, 2024 at 5:05 PM Gilad Naaman <gnaaman@drivenets.com> wrote:
>
> Remove all usage of the bare neighbour::next pointer,
> replacing them with neighbour::hash and its for_each macro.
>
> Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
> Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> ---

Reviewed-by: Eric Dumazet <edumazet@google.com>

[PATCH net-next v9 5/6] neighbour: Remove bare neighbour::next pointer

[Gilad Naaman]

Remove the now-unused neighbour::next pointer, leaving struct neighbour
solely with the hlist_node implementation.

Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 include/net/neighbour.h |  4 +-
 net/core/neighbour.c    | 90 +++++------------------------------------
 net/ipv4/arp.c          |  2 +-
 3 files changed, 12 insertions(+), 84 deletions(-)

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 94cf4f8c118f..40aac1e24c68 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -135,7 +135,6 @@ struct neigh_statistics {
 #define NEIGH_CACHE_STAT_INC(tbl, field) this_cpu_inc((tbl)->stats->field)
 
 struct neighbour {
-	struct neighbour __rcu	*next;
 	struct hlist_node	hash;
 	struct neigh_table	*tbl;
 	struct neigh_parms	*parms;
@@ -191,7 +190,6 @@ struct pneigh_entry {
 #define NEIGH_NUM_HASH_RND	4
 
 struct neigh_hash_table {
-	struct neighbour __rcu	**hash_buckets;
 	struct hlist_head	*hash_heads;
 	unsigned int		hash_shift;
 	__u32			hash_rnd[NEIGH_NUM_HASH_RND];
@@ -354,7 +352,7 @@ int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb,
 int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new, u32 flags,
 		 u32 nlmsg_pid);
 void __neigh_set_probe_once(struct neighbour *neigh);
-bool neigh_remove_one(struct neighbour *ndel, struct neigh_table *tbl);
+bool neigh_remove_one(struct neighbour *ndel);
 void neigh_changeaddr(struct neigh_table *tbl, struct net_device *dev);
 int neigh_ifdown(struct neigh_table *tbl, struct net_device *dev);
 int neigh_carrier_down(struct neigh_table *tbl, struct net_device *dev);
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index f99354d768c2..59f359c7b5e3 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -204,18 +204,12 @@ static void neigh_update_flags(struct neighbour *neigh, u32 flags, int *notify,
 	}
 }
 
-static bool neigh_del(struct neighbour *n, struct neighbour __rcu **np,
-		      struct neigh_table *tbl)
+bool neigh_remove_one(struct neighbour *n)
 {
 	bool retval = false;
 
 	write_lock(&n->lock);
 	if (refcount_read(&n->refcnt) == 1) {
-		struct neighbour *neigh;
-
-		neigh = rcu_dereference_protected(n->next,
-						  lockdep_is_held(&tbl->lock));
-		rcu_assign_pointer(*np, neigh);
 		hlist_del_rcu(&n->hash);
 		neigh_mark_dead(n);
 		retval = true;
@@ -226,29 +220,6 @@ static bool neigh_del(struct neighbour *n, struct neighbour __rcu **np,
 	return retval;
 }
 
-bool neigh_remove_one(struct neighbour *ndel, struct neigh_table *tbl)
-{
-	struct neigh_hash_table *nht;
-	void *pkey = ndel->primary_key;
-	u32 hash_val;
-	struct neighbour *n;
-	struct neighbour __rcu **np;
-
-	nht = rcu_dereference_protected(tbl->nht,
-					lockdep_is_held(&tbl->lock));
-	hash_val = tbl->hash(pkey, ndel->dev, nht->hash_rnd);
-	hash_val = hash_val >> (32 - nht->hash_shift);
-
-	np = &nht->hash_buckets[hash_val];
-	while ((n = rcu_dereference_protected(*np,
-					      lockdep_is_held(&tbl->lock)))) {
-		if (n == ndel)
-			return neigh_del(n, np, tbl);
-		np = &n->next;
-	}
-	return false;
-}
-
 static int neigh_forced_gc(struct neigh_table *tbl)
 {
 	int max_clean = atomic_read(&tbl->gc_entries) -
@@ -276,7 +247,7 @@ static int neigh_forced_gc(struct neigh_table *tbl)
 				remove = true;
 			write_unlock(&n->lock);
 
-			if (remove && neigh_remove_one(n, tbl))
+			if (remove && neigh_remove_one(n))
 				shrunk++;
 			if (shrunk >= max_clean)
 				break;
@@ -387,22 +358,15 @@ static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev,
 					lockdep_is_held(&tbl->lock));
 
 	for (i = 0; i < (1 << nht->hash_shift); i++) {
-		struct neighbour __rcu **np = &nht->hash_buckets[i];
 		struct hlist_node *tmp;
 		struct neighbour *n;
 
 		neigh_for_each_in_bucket_safe(n, tmp, &nht->hash_heads[i]) {
-			if (dev && n->dev != dev) {
-				np = &n->next;
+			if (dev && n->dev != dev)
 				continue;
-			}
-			if (skip_perm && n->nud_state & NUD_PERMANENT) {
-				np = &n->next;
+			if (skip_perm && n->nud_state & NUD_PERMANENT)
 				continue;
-			}
-			rcu_assign_pointer(*np,
-				   rcu_dereference_protected(n->next,
-						lockdep_is_held(&tbl->lock)));
+
 			hlist_del_rcu(&n->hash);
 			write_lock(&n->lock);
 			neigh_del_timer(n);
@@ -531,9 +495,7 @@ static void neigh_get_hash_rnd(u32 *x)
 
 static struct neigh_hash_table *neigh_hash_alloc(unsigned int shift)
 {
-	size_t hash_heads_size = (1 << shift) * sizeof(struct hlist_head);
-	size_t size = (1 << shift) * sizeof(struct neighbour *);
-	struct neighbour __rcu **buckets;
+	size_t size = (1 << shift) * sizeof(struct hlist_head);
 	struct hlist_head *hash_heads;
 	struct neigh_hash_table *ret;
 	int i;
@@ -542,18 +504,11 @@ static struct neigh_hash_table *neigh_hash_alloc(unsigned int shift)
 	if (!ret)
 		return NULL;
 
-	buckets = kvzalloc(size, GFP_ATOMIC);
-	if (!buckets) {
-		kfree(ret);
-		return NULL;
-	}
-	hash_heads = kvzalloc(hash_heads_size, GFP_ATOMIC);
+	hash_heads = kvzalloc(size, GFP_ATOMIC);
 	if (!hash_heads) {
-		kvfree(buckets);
 		kfree(ret);
 		return NULL;
 	}
-	ret->hash_buckets = buckets;
 	ret->hash_heads = hash_heads;
 	ret->hash_shift = shift;
 	for (i = 0; i < NEIGH_NUM_HASH_RND; i++)
@@ -567,7 +522,6 @@ static void neigh_hash_free_rcu(struct rcu_head *head)
 						    struct neigh_hash_table,
 						    rcu);
 
-	kvfree(nht->hash_buckets);
 	kvfree(nht->hash_heads);
 	kfree(nht);
 }
@@ -596,11 +550,6 @@ static struct neigh_hash_table *neigh_hash_grow(struct neigh_table *tbl,
 
 			hash >>= (32 - new_nht->hash_shift);
 
-			rcu_assign_pointer(n->next,
-					   rcu_dereference_protected(
-						new_nht->hash_buckets[hash],
-						lockdep_is_held(&tbl->lock)));
-			rcu_assign_pointer(new_nht->hash_buckets[hash], n);
 			hlist_del_rcu(&n->hash);
 			hlist_add_head_rcu(&n->hash, &new_nht->hash_heads[hash]);
 		}
@@ -705,10 +654,6 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
 		list_add_tail(&n->managed_list, &n->tbl->managed_list);
 	if (want_ref)
 		neigh_hold(n);
-	rcu_assign_pointer(n->next,
-			   rcu_dereference_protected(nht->hash_buckets[hash_val],
-						     lockdep_is_held(&tbl->lock)));
-	rcu_assign_pointer(nht->hash_buckets[hash_val], n);
 	hlist_add_head_rcu(&n->hash, &nht->hash_heads[hash_val]);
 	write_unlock_bh(&tbl->lock);
 	neigh_dbg(2, "neigh %p is created\n", n);
@@ -942,7 +887,6 @@ static void neigh_periodic_work(struct work_struct *work)
 {
 	struct neigh_table *tbl = container_of(work, struct neigh_table, gc_work.work);
 	struct neigh_hash_table *nht;
-	struct neighbour __rcu **np;
 	struct hlist_node *tmp;
 	struct neighbour *n;
 	unsigned int i;
@@ -970,8 +914,6 @@ static void neigh_periodic_work(struct work_struct *work)
 		goto out;
 
 	for (i = 0 ; i < (1 << nht->hash_shift); i++) {
-		np = &nht->hash_buckets[i];
-
 		neigh_for_each_in_bucket_safe(n, tmp, &nht->hash_heads[i]) {
 			unsigned int state;
 
@@ -981,7 +923,7 @@ static void neigh_periodic_work(struct work_struct *work)
 			if ((state & (NUD_PERMANENT | NUD_IN_TIMER)) ||
 			    (n->flags & NTF_EXT_LEARNED)) {
 				write_unlock(&n->lock);
-				goto next_elt;
+				continue;
 			}
 
 			if (time_before(n->used, n->confirmed) &&
@@ -992,9 +934,6 @@ static void neigh_periodic_work(struct work_struct *work)
 			    (state == NUD_FAILED ||
 			     !time_in_range_open(jiffies, n->used,
 						 n->used + NEIGH_VAR(n->parms, GC_STALETIME)))) {
-				rcu_assign_pointer(*np,
-					rcu_dereference_protected(n->next,
-						lockdep_is_held(&tbl->lock)));
 				hlist_del_rcu(&n->hash);
 				neigh_mark_dead(n);
 				write_unlock(&n->lock);
@@ -1002,9 +941,6 @@ static void neigh_periodic_work(struct work_struct *work)
 				continue;
 			}
 			write_unlock(&n->lock);
-
-next_elt:
-			np = &n->next;
 		}
 		/*
 		 * It's fine to release lock here, even if hash table
@@ -1951,7 +1887,7 @@ static int neigh_delete(struct sk_buff *skb, struct nlmsghdr *nlh,
 			     NETLINK_CB(skb).portid, extack);
 	write_lock_bh(&tbl->lock);
 	neigh_release(neigh);
-	neigh_remove_one(neigh, tbl);
+	neigh_remove_one(neigh);
 	write_unlock_bh(&tbl->lock);
 
 out:
@@ -3108,24 +3044,18 @@ void __neigh_for_each_release(struct neigh_table *tbl,
 	nht = rcu_dereference_protected(tbl->nht,
 					lockdep_is_held(&tbl->lock));
 	for (chain = 0; chain < (1 << nht->hash_shift); chain++) {
-		struct neighbour __rcu **np;
 		struct hlist_node *tmp;
 		struct neighbour *n;
 
-		np = &nht->hash_buckets[chain];
 		neigh_for_each_in_bucket_safe(n, tmp, &nht->hash_heads[chain]) {
 			int release;
 
 			write_lock(&n->lock);
 			release = cb(n);
 			if (release) {
-				rcu_assign_pointer(*np,
-					rcu_dereference_protected(n->next,
-						lockdep_is_held(&tbl->lock)));
 				hlist_del_rcu(&n->hash);
 				neigh_mark_dead(n);
-			} else
-				np = &n->next;
+			}
 			write_unlock(&n->lock);
 			if (release)
 				neigh_cleanup_and_release(n);
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 11c1519b3699..cb9a7ed8abd3 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1215,7 +1215,7 @@ int arp_invalidate(struct net_device *dev, __be32 ip, bool force)
 					   NEIGH_UPDATE_F_ADMIN, 0);
 		write_lock_bh(&tbl->lock);
 		neigh_release(neigh);
-		neigh_remove_one(neigh, tbl);
+		neigh_remove_one(neigh);
 		write_unlock_bh(&tbl->lock);
 	}
 
-- 
2.34.1

Re: [PATCH net-next v9 5/6] neighbour: Remove bare neighbour::next pointer

[Eric Dumazet]

On Thu, Nov 7, 2024 at 5:05 PM Gilad Naaman <gnaaman@drivenets.com> wrote:
>
> Remove the now-unused neighbour::next pointer, leaving struct neighbour
> solely with the hlist_node implementation.
>
> Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
> Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Reviewed-by: Eric Dumazet <edumazet@google.com>

[PATCH net-next v9 6/6] neighbour: Create netdev->neighbour association

[Gilad Naaman]

Create a mapping between a netdev and its neighoburs,
allowing for much cheaper flushes.

Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>
---
 .../networking/net_cachelines/net_device.rst  |  1 +
 include/linux/netdevice.h                     |  7 ++
 include/net/neighbour.h                       |  9 +-
 include/net/neighbour_tables.h                | 12 +++
 net/core/neighbour.c                          | 96 +++++++++++--------
 5 files changed, 80 insertions(+), 45 deletions(-)
 create mode 100644 include/net/neighbour_tables.h

diff --git a/Documentation/networking/net_cachelines/net_device.rst b/Documentation/networking/net_cachelines/net_device.rst
index ade50d4e67cf..15e31ece675f 100644
--- a/Documentation/networking/net_cachelines/net_device.rst
+++ b/Documentation/networking/net_cachelines/net_device.rst
@@ -188,4 +188,5 @@ u64                                 max_pacing_offload_horizon
 struct_napi_config*                 napi_config
 unsigned_long                       gro_flush_timeout
 u32                                 napi_defer_hard_irqs
+struct hlist_head                   neighbours[2]
 =================================== =========================== =================== =================== ===================================================================================
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 3c552b648b27..df4483598628 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -52,6 +52,7 @@
 #include <net/net_trackers.h>
 #include <net/net_debug.h>
 #include <net/dropreason-core.h>
+#include <net/neighbour_tables.h>
 
 struct netpoll_info;
 struct device;
@@ -2032,6 +2033,9 @@ enum netdev_reg_state {
  *	@napi_defer_hard_irqs:	If not zero, provides a counter that would
  *				allow to avoid NIC hard IRQ, on busy queues.
  *
+ *	@neighbours:	List heads pointing to this device's neighbours'
+ *			dev_list, one per address-family.
+ *
  *	FIXME: cleanup struct net_device such that network protocol info
  *	moves out.
  */
@@ -2440,6 +2444,9 @@ struct net_device {
 	 */
 	struct net_shaper_hierarchy *net_shaper_hierarchy;
 #endif
+
+	struct hlist_head neighbours[NEIGH_NR_TABLES];
+
 	u8			priv[] ____cacheline_aligned
 				       __counted_by(priv_len);
 } ____cacheline_aligned;
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 40aac1e24c68..9a832cab5b1d 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -29,6 +29,7 @@
 #include <linux/sysctl.h>
 #include <linux/workqueue.h>
 #include <net/rtnetlink.h>
+#include <net/neighbour_tables.h>
 
 /*
  * NUD stands for "neighbor unreachability detection"
@@ -136,6 +137,7 @@ struct neigh_statistics {
 
 struct neighbour {
 	struct hlist_node	hash;
+	struct hlist_node	dev_list;
 	struct neigh_table	*tbl;
 	struct neigh_parms	*parms;
 	unsigned long		confirmed;
@@ -236,13 +238,6 @@ struct neigh_table {
 	struct pneigh_entry	**phash_buckets;
 };
 
-enum {
-	NEIGH_ARP_TABLE = 0,
-	NEIGH_ND_TABLE = 1,
-	NEIGH_NR_TABLES,
-	NEIGH_LINK_TABLE = NEIGH_NR_TABLES /* Pseudo table for neigh_xmit */
-};
-
 static inline int neigh_parms_family(struct neigh_parms *p)
 {
 	return p->tbl->family;
diff --git a/include/net/neighbour_tables.h b/include/net/neighbour_tables.h
new file mode 100644
index 000000000000..bcffbe8f7601
--- /dev/null
+++ b/include/net/neighbour_tables.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NET_NEIGHBOUR_TABLES_H
+#define _NET_NEIGHBOUR_TABLES_H
+
+enum {
+	NEIGH_ARP_TABLE = 0,
+	NEIGH_ND_TABLE = 1,
+	NEIGH_NR_TABLES,
+	NEIGH_LINK_TABLE = NEIGH_NR_TABLES /* Pseudo table for neigh_xmit */
+};
+
+#endif
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 59f359c7b5e3..5e572f6eaf2c 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -60,6 +60,25 @@ static int pneigh_ifdown_and_unlock(struct neigh_table *tbl,
 static const struct seq_operations neigh_stat_seq_ops;
 #endif
 
+static struct hlist_head *neigh_get_dev_table(struct net_device *dev, int family)
+{
+	int i;
+
+	switch (family) {
+	default:
+		DEBUG_NET_WARN_ON_ONCE(1);
+		fallthrough; /* to avoid panic by null-ptr-deref */
+	case AF_INET:
+		i = NEIGH_ARP_TABLE;
+		break;
+	case AF_INET6:
+		i = NEIGH_ND_TABLE;
+		break;
+	}
+
+	return &dev->neighbours[i];
+}
+
 /*
    Neighbour hash table buckets are protected with rwlock tbl->lock.
 
@@ -211,6 +230,7 @@ bool neigh_remove_one(struct neighbour *n)
 	write_lock(&n->lock);
 	if (refcount_read(&n->refcnt) == 1) {
 		hlist_del_rcu(&n->hash);
+		hlist_del_rcu(&n->dev_list);
 		neigh_mark_dead(n);
 		retval = true;
 	}
@@ -351,48 +371,42 @@ static void pneigh_queue_purge(struct sk_buff_head *list, struct net *net,
 static void neigh_flush_dev(struct neigh_table *tbl, struct net_device *dev,
 			    bool skip_perm)
 {
-	int i;
-	struct neigh_hash_table *nht;
-
-	nht = rcu_dereference_protected(tbl->nht,
-					lockdep_is_held(&tbl->lock));
+	struct hlist_head *dev_head;
+	struct hlist_node *tmp;
+	struct neighbour *n;
 
-	for (i = 0; i < (1 << nht->hash_shift); i++) {
-		struct hlist_node *tmp;
-		struct neighbour *n;
+	dev_head = neigh_get_dev_table(dev, tbl->family);
 
-		neigh_for_each_in_bucket_safe(n, tmp, &nht->hash_heads[i]) {
-			if (dev && n->dev != dev)
-				continue;
-			if (skip_perm && n->nud_state & NUD_PERMANENT)
-				continue;
+	hlist_for_each_entry_safe(n, tmp, dev_head, dev_list) {
+		if (skip_perm && n->nud_state & NUD_PERMANENT)
+			continue;
 
-			hlist_del_rcu(&n->hash);
-			write_lock(&n->lock);
-			neigh_del_timer(n);
-			neigh_mark_dead(n);
-			if (refcount_read(&n->refcnt) != 1) {
-				/* The most unpleasant situation.
-				   We must destroy neighbour entry,
-				   but someone still uses it.
-
-				   The destroy will be delayed until
-				   the last user releases us, but
-				   we must kill timers etc. and move
-				   it to safe state.
-				 */
-				__skb_queue_purge(&n->arp_queue);
-				n->arp_queue_len_bytes = 0;
-				WRITE_ONCE(n->output, neigh_blackhole);
-				if (n->nud_state & NUD_VALID)
-					n->nud_state = NUD_NOARP;
-				else
-					n->nud_state = NUD_NONE;
-				neigh_dbg(2, "neigh %p is stray\n", n);
-			}
-			write_unlock(&n->lock);
-			neigh_cleanup_and_release(n);
+		hlist_del_rcu(&n->hash);
+		hlist_del_rcu(&n->dev_list);
+		write_lock(&n->lock);
+		neigh_del_timer(n);
+		neigh_mark_dead(n);
+		if (refcount_read(&n->refcnt) != 1) {
+			/* The most unpleasant situation.
+			 * We must destroy neighbour entry,
+			 * but someone still uses it.
+			 *
+			 * The destroy will be delayed until
+			 * the last user releases us, but
+			 * we must kill timers etc. and move
+			 * it to safe state.
+			 */
+			__skb_queue_purge(&n->arp_queue);
+			n->arp_queue_len_bytes = 0;
+			WRITE_ONCE(n->output, neigh_blackhole);
+			if (n->nud_state & NUD_VALID)
+				n->nud_state = NUD_NOARP;
+			else
+				n->nud_state = NUD_NONE;
+			neigh_dbg(2, "neigh %p is stray\n", n);
 		}
+		write_unlock(&n->lock);
+		neigh_cleanup_and_release(n);
 	}
 }
 
@@ -655,6 +669,10 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
 	if (want_ref)
 		neigh_hold(n);
 	hlist_add_head_rcu(&n->hash, &nht->hash_heads[hash_val]);
+
+	hlist_add_head_rcu(&n->dev_list,
+			   neigh_get_dev_table(dev, tbl->family));
+
 	write_unlock_bh(&tbl->lock);
 	neigh_dbg(2, "neigh %p is created\n", n);
 	rc = n;
@@ -935,6 +953,7 @@ static void neigh_periodic_work(struct work_struct *work)
 			     !time_in_range_open(jiffies, n->used,
 						 n->used + NEIGH_VAR(n->parms, GC_STALETIME)))) {
 				hlist_del_rcu(&n->hash);
+				hlist_del_rcu(&n->dev_list);
 				neigh_mark_dead(n);
 				write_unlock(&n->lock);
 				neigh_cleanup_and_release(n);
@@ -3054,6 +3073,7 @@ void __neigh_for_each_release(struct neigh_table *tbl,
 			release = cb(n);
 			if (release) {
 				hlist_del_rcu(&n->hash);
+				hlist_del_rcu(&n->dev_list);
 				neigh_mark_dead(n);
 			}
 			write_unlock(&n->lock);
-- 
2.34.1

Re: [PATCH net-next v9 6/6] neighbour: Create netdev->neighbour association

[Eric Dumazet]

On Thu, Nov 7, 2024 at 5:05 PM Gilad Naaman <gnaaman@drivenets.com> wrote:
>
> Create a mapping between a netdev and its neighoburs,
> allowing for much cheaper flushes.
>
> Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>

Reviewed-by: Eric Dumazet <edumazet@google.com>

Re: [PATCH net-next v9 6/6] neighbour: Create netdev->neighbour association

[Kuniyuki Iwashima]

From: Gilad Naaman <gnaaman@drivenets.com>
Date: Thu,  7 Nov 2024 16:04:43 +0000
> Create a mapping between a netdev and its neighoburs,
> allowing for much cheaper flushes.
> 
> Signed-off-by: Gilad Naaman <gnaaman@drivenets.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Re: [PATCH net-next v9 0/6] Improve neigh_flush_dev performance

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu,  7 Nov 2024 16:04:37 +0000 you wrote:
> This patchsets improves the performance of neigh_flush_dev.
> 
> Currently, the only way to implement it requires traversing
> all neighbours known to the kernel, across all network-namespaces.
> 
> This means that some flows are slowed down as a function of neigh-scale,
> even if the specific link they're handling has little to no neighbours.
> 
> [...]

Here is the summary with links:
  - [net-next,v9,1/6] neighbour: Add hlist_node to struct neighbour
    https://git.kernel.org/netdev/net-next/c/41b3caa7c076
  - [net-next,v9,2/6] neighbour: Define neigh_for_each_in_bucket
    https://git.kernel.org/netdev/net-next/c/d7ddee1a522d
  - [net-next,v9,3/6] neighbour: Convert seq_file functions to use hlist
    https://git.kernel.org/netdev/net-next/c/00df5e1a3fdf
  - [net-next,v9,4/6] neighbour: Convert iteration to use hlist+macro
    https://git.kernel.org/netdev/net-next/c/0e3bcb0f78a0
  - [net-next,v9,5/6] neighbour: Remove bare neighbour::next pointer
    https://git.kernel.org/netdev/net-next/c/a01a67ab2fff
  - [net-next,v9,6/6] neighbour: Create netdev->neighbour association
    https://git.kernel.org/netdev/net-next/c/f7f52738637f

You are awesome, thank you!
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