fork: free vmapped stacks in cache when cpus are offline

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 cached stacks may remain unfreed even when cpu
are offline.  By adding a cpu hotplug callback to free the cached stacks
when a cpu goes offline, the pages of the cached stacks are not wasted.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Hoeun Ryu <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Mateusz Guzik <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions