6.6-stable review patch. If anyone has any objections, please let me know.
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From: Ido Schimmel idosch@nvidia.com
[ Upstream commit 20c76dadc783759fd3819d289c72be590660cc8b ]
FDB entries are allocated in an atomic context as they can be added from the data path when learning is enabled.
After converting the FDB hash table to rhashtable, the insertion rate will be much higher (*) which will entail a much higher rate of per-CPU allocations via dst_cache_init().
When adding a large number of entries (e.g., 256k) in a batch, a small percentage (< 0.02%) of these per-CPU allocations will fail [1]. This does not happen with the current code since the insertion rate is low enough to give the per-CPU allocator a chance to asynchronously create new chunks of per-CPU memory.
Given that:
a. Only a small percentage of these per-CPU allocations fail.
b. The scenario where this happens might not be the most realistic one.
c. The driver can work correctly without dst caches. The dst_cache_*() APIs first check that the dst cache was properly initialized.
d. The dst caches are not always used (e.g., 'tos inherit').
It seems reasonable to not treat these allocation failures as fatal.
Therefore, do not bail when dst_cache_init() fails and suppress warnings by specifying '__GFP_NOWARN'.
[1] percpu: allocation failed, size=40 align=8 atomic=1, atomic alloc failed, no space left
(*) 97% reduction in average latency of vxlan_fdb_update() when adding 256k entries in a batch.
Reviewed-by: Petr Machata petrm@nvidia.com Signed-off-by: Ido Schimmel idosch@nvidia.com Link: https://patch.msgid.link/20250415121143.345227-14-idosch@nvidia.com Reviewed-by: Nikolay Aleksandrov razor@blackwall.org Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/vxlan/vxlan_core.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c index 2ed879a0abc6c..1b6b6acd34894 100644 --- a/drivers/net/vxlan/vxlan_core.c +++ b/drivers/net/vxlan/vxlan_core.c @@ -606,10 +606,10 @@ static int vxlan_fdb_append(struct vxlan_fdb *f, if (rd == NULL) return -ENOMEM;
- if (dst_cache_init(&rd->dst_cache, GFP_ATOMIC)) { - kfree(rd); - return -ENOMEM; - } + /* The driver can work correctly without a dst cache, so do not treat + * dst cache initialization errors as fatal. + */ + dst_cache_init(&rd->dst_cache, GFP_ATOMIC | __GFP_NOWARN);
rd->remote_ip = *ip; rd->remote_port = port;