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

[Stefan Hajnoczi]

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).

Stefan

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