RE: Question about ip_defrag

["liujian (CE)" <liujian56@huawei.com>]

Best Regards,
liujian


> -----Original Message-----
> From: liujian (CE)
> Sent: Tuesday, August 29, 2017 3:39 PM
> To: 'Florian Westphal'
> Cc: Jesper Dangaard Brouer; davem@davemloft.net; kuznet@ms2.inr.ac.ru;
> yoshfuji@linux-ipv6.org; elena.reshetova@intel.com; edumazet@google.com;
> netdev@vger.kernel.org; Wangkefeng (Kevin); weiyongjun (A)
> Subject: RE: Question about ip_defrag
> 
> 
> 
> > -----Original Message-----
> > From: netdev-owner@vger.kernel.org
> > [mailto:netdev-owner@vger.kernel.org]
> > On Behalf Of Florian Westphal
> > Sent: Monday, August 28, 2017 10:01 PM
> > To: liujian (CE)
> > Cc: Jesper Dangaard Brouer; davem@davemloft.net; kuznet@ms2.inr.ac.ru;
> > yoshfuji@linux-ipv6.org; elena.reshetova@intel.com;
> > edumazet@google.com; netdev@vger.kernel.org; Wangkefeng (Kevin);
> > weiyongjun (A)
> > Subject: Re: Question about ip_defrag
> >
> > liujian (CE) <liujian56@huawei.com> wrote:
> > > Hi
> > >
> > > I checked our 3.10 kernel, we had backported all percpu_counter bug
> > > fix in
> > lib/percpu_counter.c and include/linux/percpu_counter.h.
> > > And I check 4.13-rc6, also has the issue if NIC's rx cpu num big enough.
> > >
> > > > > > > the issue:
> > > > > > > Ip_defrag fail caused by frag_mem_limit reached
> > 4M(frags.high_thresh).
> > > > > > > At this moment,sum_frag_mem_limit is about 10K.
> > >
> > > So should we change ipfrag high/low thresh to a reasonable value ?
> > > And if it is, is there a standard to change the value?
> >
> > Each cpu can have frag_percpu_counter_batch bytes rest doesn't know
> > about so with 64 cpus that is ~8 mbyte.
> >
> > possible solutions:
> > 1. reduce frag_percpu_counter_batch to 16k or so 2. make both low and
> > high thresh depend on NR_CPUS
> >
> Thank you for your reply.
> 
> > liujian, does this change help in any way?
> 
> I will have a try.

Now, I have not the real environment. 
I use iperf generate fragment packets; 
and I always change NIC rx irq's affinity cpu, to make sure frag_mem_limit reach to thresh.
my test machine, CPU num is 384.
As above , test the patch , seemingly , there is no improving...
Check /proc/net/snmp, there is no significant difference.
maybe we should find a good test method!

root@RH8100-V3:/proc/net# cat sockstat
sockets: used 1386
TCP: inuse 3 orphan 0 tw 0 alloc 4 mem 1
UDP: inuse 44 mem 42
UDPLITE: inuse 0
RAW: inuse 0
FRAG: inuse 1 memory 34336, 3144424.
 

> > diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
> > --- a/net/ipv4/inet_fragment.c
> > +++ b/net/ipv4/inet_fragment.c
> > @@ -123,6 +123,17 @@ static bool inet_fragq_should_evict(const struct
> > inet_frag_queue *q)
> >  	       frag_mem_limit(q->net) >= q->net->low_thresh;  }
> >
> > +/* ->mem batch size is huge, this can cause severe discrepancies
> > + * between actual value (sum of pcpu values) and the global estimate.
> > + *
> > + * Use a smaller batch to give an opportunity for the global estimate
> > + * to more accurately reflect current state.
> > + */
> > +static void update_frag_mem_limit(struct netns_frags *nf, unsigned
> > +int
> > +batch) {
> > +	 percpu_counter_add_batch(&nf->mem, 0, batch); }
> > +
> >  static unsigned int
> >  inet_evict_bucket(struct inet_frags *f, struct inet_frag_bucket *hb)
> > { @@
> > -146,8 +157,12 @@ inet_evict_bucket(struct inet_frags *f, struct
> > inet_frag_bucket *hb)
> >
> >  	spin_unlock(&hb->chain_lock);
> >
> > -	hlist_for_each_entry_safe(fq, n, &expired, list_evictor)
> > +	hlist_for_each_entry_safe(fq, n, &expired, list_evictor) {
> > +		struct netns_frags *nf = fq->net;
> > +
> >  		f->frag_expire((unsigned long) fq);
> > +		update_frag_mem_limit(nf, 1);
> 
> > +	}
> >
> >  	return evicted;
> >  }
> > @@ -396,8 +411,10 @@ struct inet_frag_queue *inet_frag_find(struct
> > netns_frags *nf,
> >  	struct inet_frag_queue *q;
> >  	int depth = 0;
> >
> > -	if (frag_mem_limit(nf) > nf->low_thresh)
> > +	if (frag_mem_limit(nf) > nf->low_thresh) {
> >  		inet_frag_schedule_worker(f);
> > +		update_frag_mem_limit(nf, SKB_TRUESIZE(1500) * 16);
> > +	}
> >
> >  	hash &= (INETFRAGS_HASHSZ - 1);
> >  	hb = &f->hash[hash];
> > @@ -416,6 +433,8 @@ struct inet_frag_queue *inet_frag_find(struct
> > netns_frags *nf,
> >  	if (depth <= INETFRAGS_MAXDEPTH)
> >  		return inet_frag_create(nf, f, key);
> >
> > +	update_frag_mem_limit(nf, 1);
> > +
> >  	if (inet_frag_may_rebuild(f)) {
> >  		if (!f->rebuild)
> >  			f->rebuild = true;