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netns: optimize netns cleaning by batching unhash_nsid calls

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Currently, unhash_nsid() scans the entire system for each netns being
killed, leading to O(L_dying_net * M_alive_net * N_id) complexity, as
__peernet2id() also performs a linear search in the IDR.

Optimize this to O(M_alive_net * N_id) by batching unhash operations. Move
unhash_nsid() out of the per-netns loop in cleanup_net() to perform a
single-pass traversal over survivor namespaces.

Identify dying peers by an 'is_dying' flag, which is set under net_rwsem
write lock after the netns is removed from the global list. This batches
the unhashing work and eliminates the O(L_dying_net) multiplier.

To minimize the impact on struct net size, 'is_dying' is placed in an
existing hole after 'hash_mix' in struct net.

Use a restartable idr_get_next() loop for iteration. This avoids the
unsafe modification issue inherent to idr_for_each() callbacks and allows
dropping the nsid_lock to safely call sleepy rtnl_net_notifyid().

Clean up redundant nsid_lock and simplify the destruction loop now that
unhashing is centralized.

Signed-off-by: Qiliang Yuan <yuanql9@chinatelecom.cn>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260204074854.3506916-1-realwujing@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Qiliang Yuan
2026-02-04 02:48:42 -05:00
committed by Jakub Kicinski
parent 24cf78c738
commit 7acee67a6b
2 changed files with 22 additions and 13 deletions
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1
include/net/net_namespace.h
View File

@@ -121,6 +121,7 @@ struct net {
* it is critical that it is on a read_mostly cache line.
*/
u32 hash_mix;
bool is_dying;
struct net_device *loopback_dev; /* The loopback */

34
net/core/net_namespace.c
View File

@@ -624,9 +624,10 @@ void net_ns_get_ownership(const struct net *net, kuid_t *uid, kgid_t *gid)
}
EXPORT_SYMBOL_GPL(net_ns_get_ownership);
static void unhash_nsid(struct net *net, struct net *last)
static void unhash_nsid(struct net *last)
{
struct net *tmp;
struct net *tmp, *peer;
/* This function is only called from cleanup_net() work,
* and this work is the only process, that may delete
* a net from net_namespace_list. So, when the below
@@ -634,22 +635,26 @@ static void unhash_nsid(struct net *net, struct net *last)
* use for_each_net_rcu() or net_rwsem.
*/
for_each_net(tmp) {
int id;
int id = 0;
spin_lock(&tmp->nsid_lock);
id = __peernet2id(tmp, net);
if (id >= 0)
idr_remove(&tmp->netns_ids, id);
spin_unlock(&tmp->nsid_lock);
if (id >= 0)
rtnl_net_notifyid(tmp, RTM_DELNSID, id, 0, NULL,
while ((peer = idr_get_next(&tmp->netns_ids, &id))) {
int curr_id = id;
id++;
if (!peer->is_dying)
continue;
idr_remove(&tmp->netns_ids, curr_id);
spin_unlock(&tmp->nsid_lock);
rtnl_net_notifyid(tmp, RTM_DELNSID, curr_id, 0, NULL,
GFP_KERNEL);
spin_lock(&tmp->nsid_lock);
}
spin_unlock(&tmp->nsid_lock);
if (tmp == last)
break;
}
spin_lock(&net->nsid_lock);
idr_destroy(&net->netns_ids);
spin_unlock(&net->nsid_lock);
}
static LLIST_HEAD(cleanup_list);
@@ -674,6 +679,7 @@ static void cleanup_net(struct work_struct *work)
llist_for_each_entry(net, net_kill_list, cleanup_list) {
ns_tree_remove(net);
list_del_rcu(&net->list);
net->is_dying = true;
}
/* Cache last net. After we unlock rtnl, no one new net
* added to net_namespace_list can assign nsid pointer
@@ -688,8 +694,10 @@ static void cleanup_net(struct work_struct *work)
last = list_last_entry(&net_namespace_list, struct net, list);
up_write(&net_rwsem);
unhash_nsid(last);
llist_for_each_entry(net, net_kill_list, cleanup_list) {
unhash_nsid(net, last);
idr_destroy(&net->netns_ids);
list_add_tail(&net->exit_list, &net_exit_list);
}