Re: [PATCH 1/3] lockdep: Apply crossrelease to PG_locked locks

From: Michal Hocko
Date: Thu Nov 16 2017 - 08:08:02 EST

On Thu 16-11-17 21:48:05, Byungchul Park wrote:
> On 11/16/2017 9:02 PM, Michal Hocko wrote:
> > for each struct page. So you are doubling the size. Who is going to
> > enable this config option? You are moving this to page_ext in a later
> > patch which is a good step but it doesn't go far enough because this
> > still consumes those resources. Is there any problem to make this
> > kernel command line controllable? Something we do for page_owner for
> > example?
> Sure. I will add it.
> > Also it would be really great if you could give us some measures about
> > the runtime overhead. I do not expect it to be very large but this is
> The major overhead would come from the amount of additional memory
> consumption for 'lockdep_map's.


> Do you want me to measure the overhead by the additional memory
> consumption?
> Or do you expect another overhead?

I would be also interested how much impact this has on performance. I do
not expect it would be too large but having some numbers for cache cold
parallel kbuild or other heavy page lock workloads.
Michal Hocko