[Devel] [PATCH RHEL9 COMMIT] ve/net/neighbour: restore hashtable size limit

[Konstantin Khorenko]

The commit is pushed to "branch-rh9-5.14.0-362.18.1.vz9.40.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh9-5.14.0-362.18.1.vz9.40.5
------>
commit 9ed7d66ec22a3d83eea24246ab75b64c7e48a233
Author: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
Date:   Mon Apr 8 15:29:28 2024 +0300

    ve/net/neighbour: restore hashtable size limit
    
    With counters for neigh entries per VE introduced in
     https://virtuozzo.atlassian.net/browse/PSBM-87155
    tbl->entries, which served as limit of hashtable size,
    become unlimited, so the table can grow very large.
    
    Table is allocated via __get_free_pages() which allocates
    continious regions of phys mem and large order allocations
    are very likely to fail - which was observed in the issue.
    
    To address this limit the allocation order to 5.
    
    Fixes: 019712d0d37d ("ve/net/neighbour: per-ct limit for neighbour entries")
    https://virtuozzo.atlassian.net/browse/PSBM-153199
    https://pmc.acronis.work/browse/VSTOR-81287
    Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
    Feature: net: make the neighbor entries limit per-CT
---
 net/core/neighbour.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 9d1302fed0cf..4239afe253ee 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -725,7 +725,13 @@ ___neigh_create(struct neigh_table *tbl, const void *pkey,
 	nht = rcu_dereference_protected(tbl->nht,
 					lockdep_is_held(&tbl->lock));
 
-	if (atomic_read(&tbl->entries) > (1 << nht->hash_shift))
+	/*
+	 * Since entries can grow unlimited we limit the size of the hash table
+	 * here. __get_free_pages allocates continious regions of phys mem
+	 * and orders above 10 are very hard to satisfy. We limit the size to 5
+	 * as it is the middle ground
+	 */
+	if (nht->hash_shift < 5 && atomic_read(&tbl->entries) > (1 << nht->hash_shift))
 		nht = neigh_hash_grow(tbl, nht->hash_shift + 1);
 
 	hash_val = tbl->hash(n->primary_key, dev, nht->hash_rnd) >> (32 - nht->hash_shift);