[Devel] [PATCH vz7] neighbour: restore hashtable size limit

[Alexander Atanasov]

With counters fro 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
continuous 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
Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
---
 net/core/neighbour.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

v1->v2: fix spelling type, add defines to explain checks

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 9e53bb3d1c81..63cadf2d022b 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -641,7 +641,14 @@ struct neighbour *__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 continuous 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
+	 */
+	#define GFP_SAFEZONE_LIMIT 5
+	#define GFP_IN_SAFEZONE(x) ((x) < GFP_SAFEZONE_LIMIT)
+	if (GFP_IN_SAFEZONE(nht->hash_shift) && atomic_read(&tbl->entries) > (1 << nht->hash_shift))
 		nht = neigh_hash_grow(tbl, nht->hash_shift + 1);
 
 	hash_val = tbl->hash(pkey, dev, nht->hash_rnd) >> (32 - nht->hash_shift);
-- 
2.39.3