mm/vmalloc.c: change purge_ndoes as local static variable

mm/vmalloc.c: change purge_ndoes as local static variable

Patch series "mm/vmalloc.c: code cleanup and improvements", v2.

These changes were made from code inspection in mm/vmalloc.c.

This patch (of 5):

Static variable 'purge_ndoes' is defined in global scope, while it's only
used in function __purge_vmap_area_lazy().  It mainly serves to avoid
memory allocation repeatedly, especially when NR_CPUS is big.

While a local static variable can also satisfy the demand, and can improve
code readibility.  Hence move its definition into
__purge_vmap_area_lazy().

Link: https://lkml.kernel.org/r/20250418223653.243436-1-bhe@redhat.com
Link: https://lkml.kernel.org/r/20250418223653.243436-2-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reviewed-by: Shivank Garg <shivankg@amd.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>