On Mon, 28 Aug 2017 16:00:32 +0200
Florian Westphal <f...@strlen.de> wrote:
> liujian (CE) <liujia...@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
To me it looks like we/I have been using the wrong API for comparing
against percpu_counters. I guess we should have used
__percpu_counter_compare().
/*
* Compare counter against given value.
* Return 1 if greater, 0 if equal and -1 if less
*/
int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
{
s64 count;
count = percpu_counter_read(fbc);
/* Check to see if rough count will be sufficient for comparison */
if (abs(count - rhs) > (batch * num_online_cpus())) {
if (count > rhs)
return 1;
else
return -1;
}
/* Need to use precise count */
count = percpu_counter_sum(fbc);
if (count > rhs)
return 1;
else if (count < rhs)
return -1;
else
return 0;
}
EXPORT_SYMBOL(__percpu_counter_compare);
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
