Re: [REGRESSION] 6.18.14 netfilter/nftables consumes way more memory

[Pablo Neira Ayuso]

Hi Chris,

On Thu, Mar 05, 2026 at 10:28:49AM -0600, Chris Arges wrote:
> I noticed after I sent, thanks for fixing.
> > Hi,
> > 
> > On Wed, Mar 04, 2026 at 11:50:54AM -0600, Chris Arges wrote:
> > > Hello,
> > > 
> > > We've noticed significant slab unreclaimable memory increase after upgrading
> > > from 6.18.12 to 6.18.15. Other memory values look fairly close, but in my
> > > testing slab unreclaimable goes from 1.7 GB to 4.9 GB on machines.
> > 
> > From where are you collecting these memory consumption numbers?
> > 
> 
> These numbers come from the cgroup's memory.stat:
> ```
> $ cat /sys/fs/cgroup/path/to/service/memory.stat | grep slab
> slab_reclaimable 35874232
> slab_unreclaimable 5343553056
> slab 5379427288
> ```
> 
> > > Our use case is having nft rules like below, but adding them to 1000s of
> > > network namespaces. This is essentially running `nft -f` for all these
> > > namespaces every minute.
> > 
> > Those numbers for only 1000? That is too little number of entries for
> > such increase in memory usage that you report.
> > 
> 
> For this workload that I suspect (since its in the cgroup) it has the following
> characteristics:
> - 1000s of namespaces
> - 1000s of CIDRs in ip list per namespace
> - Updating everything frequently (<1m)

I see what is going on, my resize logic is not correct. This is
increasing the size for each new transaction, then the array is
getting larger and larger on each transaction update.

Could you please give a try to this patch?

Thanks.
diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
index 853ff30a208c..4462ac48fdfa 100644
--- a/net/netfilter/nft_set_rbtree.c
+++ b/net/netfilter/nft_set_rbtree.c
@@ -646,7 +646,7 @@ static int nft_array_may_resize(const struct nft_set *set)
 	struct nft_array *array;
 
 	if (!priv->array_next) {
-		array = nft_array_alloc(nelems + NFT_ARRAY_EXTRA_SIZE);
+		array = nft_array_alloc(nelems);
 		if (!array)
 			return -ENOMEM;