netdev - Re: Question about ip

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Date:   Tue, 29 Aug 2017 15:46:35 +0200
From:   Florian Westphal <fw@...len.de>
To:     "liujian (CE)" <liujian56@...wei.com>
Cc:     Florian Westphal <fw@...len.de>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Wangkefeng (Kevin)" <wangkefeng.wang@...wei.com>,
        "weiyongjun (A)" <weiyongjun1@...wei.com>
Subject: Re: Question about ip_defrag

liujian (CE) <liujian56@...wei.com> wrote:

[ trimming cc list ]

> 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.

Oh well, that explains it.

> > > +	if (frag_mem_limit(nf) > nf->low_thresh) {
> > >  		inet_frag_schedule_worker(f);
> > > +		update_frag_mem_limit(nf, SKB_TRUESIZE(1500) * 16);
> > > +	}

You need to reduce this to a lower value.
Your cpu count * batch_value needs to be less than
low_thresh to avoid problems.

Wtih 384 cpus its close to 12 mbyte...

Perhaps do this:

update_frag_mem_limit(nf, 2 * 1024*1024 / NR_CPUS);


However, I think its better to revert the percpu counter change and
move back to a single atomic_t count.