Re: [Qemu-devel] [PATCH] rcu: reduce half heap memory size by malloc_trim()

[Zhong Yang]

On Mon, Nov 20, 2017 at 02:03:44PM +0000, Stefan Hajnoczi wrote:
> On Mon, Nov 20, 2017 at 04:41:41PM +0800, Zhong Yang wrote:
> > On Fri, Nov 17, 2017 at 01:54:09PM +0000, Stefan Hajnoczi wrote:
> > > On Fri, Nov 17, 2017 at 02:23:34PM +0800, Yang Zhong wrote:
> > > > @@ -272,6 +273,9 @@ static void *call_rcu_thread(void *opaque)
> > > >              node->func(node);
> > > >          }
> > > >          qemu_mutex_unlock_iothread();
> > > > +#ifdef CONFIG_LINUX
> > > > +        malloc_trim(0);
> > > > +#endif
> > > 
> > > It is important that the rcu thread isn't overzealous in minimizing heap
> > > size if that means ordinary malloc(3) calls will experience latency
> > > spikes.  Please leave a few MB free so that malloc(3) doesn't take the
> > > slow path.
> > > 
> >   Hello Stefan,
> > 
> >   From the Qemu bootup procedure, the qemu malloc chunk memory from OS, not
> >   from glibc free list which is freed before by Qemu. Maybe there are some 
> >   issues in glibc memory mechanism. I will continue to fine this parameter
> >   to get better balance, Many thanks!
> 
> I was suggesting malloc_trim(4 * 1024 * 1024) or similar instead of
> malloc_trim(0).
>  
  Hello Stefan,

  Thanks for your suggestion!
  I tried your suggested changes, malloc_trim(4 * 1024 * 1024), the heap size 
with
  this change almost same with malloc_trim(0), thanks!

  Regards,

  Yang   
 
> Stefan