On Sat 04-02-17 11:01:32, Hoeun Ryu wrote: > On Sat, Feb 4, 2017 at 2:52 AM, Andy Lutomirski <[email protected]> wrote: > > On Fri, Feb 3, 2017 at 8:42 AM, Hoeun Ryu <[email protected]> wrote: > >> On Sat, Feb 4, 2017 at 12:39 AM, Michal Hocko <[email protected]> wrote: > >>> On Sat 04-02-17 00:30:05, Hoeun Ryu wrote: > >>>> Using virtually mapped stack, kernel stacks are allocated via vmalloc. > >>>> In the current implementation, two stacks per cpu can be cached when > >>>> tasks are freed and the cached stacks are used again in task > >>>> duplications. > >>>> but the array for the cached stacks is statically allocated by per-cpu > >>>> api. > >>>> In this new implementation, the array for the cached stacks are > >>>> dynamically > >>>> allocted and freed by cpu hotplug callbacks and the cached stacks are > >>>> freed > >>>> when cpu is down. setup for cpu hotplug is established in fork_init(). > >>> > >>> Why do we want this? I can see that the follow up patch makes the number > >>> configurable but the changelog doesn't describe the motivation for that. > >>> Which workload would benefit from a higher value? > >>> > >> > >> The key difference of this implementation, the cached stacks for a cpu > >> is freed when a cpu is down. > >> so the cached stacks are no longer wasted. > >> In the current implementation, the cached stacks for a cpu still > >> remain on the system when a cpu is down. > >> I think we could imagine what if a machine has many cpus and someone > >> wants to have bigger size of stack caches. > > > > Then how about just registering a simple hotplug hook to free the > > stacks without worrying about freeing the tiny array as well? > > > > Michal, What do you think about it. it sounds fair enough.
This is what I've tried to suggest in the other reply. -- Michal Hocko SUSE Labs
