netdev - Re: [PATCHv2 RFC net-next 08/14] ipvs: use resizable hash table for services

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Message-ID: <31a84455-86e7-c99f-7011-5385bbe0179d@ssi.bg>
Date: Wed, 17 Jan 2024 15:09:55 +0200 (EET)
From: Julian Anastasov <ja@....bg>
To: Simon Horman <horms@...nel.org>
cc: lvs-devel@...r.kernel.org, netfilter-devel@...r.kernel.org,
        netdev@...r.kernel.org, Dust Li <dust.li@...ux.alibaba.com>,
        Jiejian Wu <jiejian@...ux.alibaba.com>,
        Jiri Wiesner <jwiesner@...e.de>
Subject: Re: [PATCHv2 RFC net-next 08/14] ipvs: use resizable hash table for
 services


	Hello,

On Wed, 17 Jan 2024, Simon Horman wrote:

> On Tue, Dec 12, 2023 at 06:24:38PM +0200, Julian Anastasov wrote:
> > Make the hash table for services resizable in the bit range of 4-20.
> > Table is attached only while services are present. Resizing is done
> > by delayed work based on load (the number of hashed services).
> > Table grows when load increases 2+ times (above 12.5% with factor=3)
> > and shrinks 8+ times when load decreases 16+ times (below 0.78%).
> > 
> > Switch to jhash hashing to reduce the collisions for multiple
> > services.
> > 
> > Add a hash_key field into the service that includes table ID and
> > bucket ID. This helps the lookup and delete operations.
> > 
> > Signed-off-by: Julian Anastasov <ja@....bg>
> 
> ...
> 
> > @@ -391,18 +440,29 @@ static inline struct ip_vs_service *
> >  __ip_vs_service_find(struct netns_ipvs *ipvs, int af, __u16 protocol,
> >  		     const union nf_inet_addr *vaddr, __be16 vport)
> >  {
> > -	unsigned int hash;
> > +	DECLARE_IP_VS_RHT_WALK_BUCKET_RCU();
> > +	struct hlist_bl_head *head;
> >  	struct ip_vs_service *svc;
> > -
> > -	/* Check for "full" addressed entries */
> > -	hash = ip_vs_svc_hashkey(ipvs, af, protocol, vaddr, vport);
> > -
> > -	hlist_for_each_entry_rcu(svc, &ipvs->svc_table[hash], s_list) {
> > -		if (svc->af == af && ip_vs_addr_equal(af, &svc->addr, vaddr) &&
> > -		    svc->port == vport && svc->protocol == protocol &&
> > -		    !svc->fwmark) {
> > -			/* HIT */
> > -			return svc;
> > +	struct ip_vs_rht *t, *p;
> > +	struct hlist_bl_node *e;
> > +	u32 hash, hash_key;
> > +
> > +	ip_vs_rht_for_each_table_rcu(ipvs->svc_table, t, p) {
> > +		/* Check for "full" addressed entries */
> > +		hash = ip_vs_svc_hashval(t, af, protocol, vaddr, vport);
> > +
> > +		hash_key = ip_vs_rht_build_hash_key(t, hash);
> > +		ip_vs_rht_walk_bucket_rcu(t, hash_key, head) {
> > +			hlist_bl_for_each_entry_rcu(svc, e, head, s_list) {
> 
> Hi Julian,
> 
> Smatch thinks that head is used uninitialised here.
> This does seem to be the case to me too.

	It would crash and not find svc if that was true. May be it is 
caused by the complex 'if (INIT then FAIL) {} else ANYTHING' 
construct used in ip_vs_rht_walk_bucket_rcu() which allows
'if () {} else for () for () for () ...'.

Regards

--
Julian Anastasov <ja@....bg>