You possibly want to adjust the subject, instead of shrink I would use "dynamically allocate" or similar.
On Mon, Mar 09, 2026 at 04:35:34PM +0100, Jan Beulich wrote: > This NR_CPUS-dimensioned array is likely unused on most installations. > Therefore it is especially wasteful for it to consume more space than > really needed. Allocate it dynamically ahead of registering the hooks. > > Further the array having all fields set to -1 is actually useless. Nothing > relies on it, and core_parking_remove() doesn't restore the sentinel for > vacated slots. Drop the initializers altogether, rather than replacing > them. > > Also take the opportunity and update an adjacent variable's type, where > a fixed-width type was pretty clearly inappropriate to use. > > Finally drop the redundant initializer from core_parking_init(). > > Signed-off-by: Jan Beulich <[email protected]> > --- > I assume there is a reason this is acting (mostly) as a LIFO. Else a > simple cpumask_t would suffice. > > num_possible_cpus() would be the more correct thing to use as array > dimension, yet we don't maintain cpu_possible_map on x86. > --- > v2: Use dynamic allocation. > > --- a/xen/common/core_parking.c > +++ b/xen/common/core_parking.c > @@ -20,6 +20,7 @@ > #include <xen/cpumask.h> > #include <xen/init.h> > #include <xen/param.h> > +#include <xen/xvmalloc.h> > > #include <asm/smp.h> > > @@ -27,8 +28,8 @@ > #define CORE_PARKING_DECREMENT 2 > > static DEFINE_SPINLOCK(accounting_lock); > -static uint32_t cur_idle_nums; > -static unsigned int core_parking_cpunum[NR_CPUS] = {[0 ... NR_CPUS-1] = -1}; > +static unsigned int cur_idle_nums; > +static unsigned int *__ro_after_init core_parking_cpunum; Don't you need some kind of check in core_parking_remove() to prevent a NULL pointer dereference if core_parking_cpunum hasn't been allocated? Callers of XEN_SYSCTL_cpu_hotplug can set fn = smt_up_down_helper, and that would call core_parking_remove(). core_parking_helper() already contains a check that prevents accessing core_parking_cpunum if no policy has been registered. Thanks, Roger.
