Re: BUG: MAX_STACK_TRACE_ENTRIES too low! (2)

[Bart Van Assche]

On 7/12/19 1:55 AM, Peter Zijlstra wrote:
> On Thu, Jul 11, 2019 at 11:53:12AM -0700, Bart Van Assche wrote:
> > On 7/10/19 3:09 PM, Peter Zijlstra wrote:
> > > One thing I mentioned when Thomas did the unwinder API changes was
> > > trying to move lockdep over to something like stackdepot.
> > >
> > > We can't directly use stackdepot as is, because it uses locks and memory
> > > allocation, but we could maybe add a lower level API to it and use that
> > > under the graph_lock() on static storage or something.
> > >
> > > Otherwise we'll have to (re)implement something like it.
> > >
> > > I've not looked at it in detail.
> >
> > Hi Peter,
> >
> > Is something like the untested patch below perhaps what you had in mind?
>
> Most excellent, yes! Now I suppose the $64000 question is if it actually
> reduces the amount of storage we use for stack traces..
>
> Seems to boot just fine.. :-)

Hi Peter,

On my setup after some time the space occupied by stack traces stabilizes
to the following:

# grep stack /proc/lockdep_stats
 stack-trace entries:                169456 [max: 524288]
 number of stack traces:        9073
 number of stack hash chains:   6980

I think these numbers show that there are some but not too many hash
collisions (the code for the hash statistics was added after I e-mailed my
patch).

Bart.