Re: Question about ip_defrag

From: Florian Westphal <fw@strlen.de>
To: "liujian (CE)" <liujian56@huawei.com>
Cc: Florian Westphal <fw@strlen.de>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"Wangkefeng (Kevin)" <wangkefeng.wang@huawei.com>,
	"weiyongjun (A)" <weiyongjun1@huawei.com>
Subject: Re: Question about ip_defrag
Date: Tue, 29 Aug 2017 15:46:35 +0200	[thread overview]
Message-ID: <20170829134635.GB9993@breakpoint.cc> (raw)
In-Reply-To: <4F88C5DDA1E80143B232E89585ACE27D018F4850@DGGEMA502-MBX.china.huawei.com>

liujian (CE) <liujian56@huawei.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.