Messages in this thread | | | From | Hoeun Ryu <> | Date | Sun, 5 Feb 2017 22:23:06 +0900 | Subject | Re: [PATCH 1/3] fork: dynamically allocate cache array for vmapped stacks using cpuhp |
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On Sun, Feb 5, 2017 at 7:18 PM, Michal Hocko <mhocko@kernel.org> wrote: > On Sat 04-02-17 11:01:32, Hoeun Ryu wrote: >> On Sat, Feb 4, 2017 at 2:52 AM, Andy Lutomirski <luto@amacapital.net> wrote: >> > On Fri, Feb 3, 2017 at 8:42 AM, Hoeun Ryu <hoeun.ryu@gmail.com> wrote: >> >> On Sat, Feb 4, 2017 at 12:39 AM, Michal Hocko <mhocko@kernel.org> 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.
OK, I'll work on patch1/2 again and drop patch3.
> -- > Michal Hocko > SUSE Labs
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