[RFC PATCH 7/9] mm: use read_lock for free path

Daniel Jordan's patch has made it possible for multiple threads to operate on a global list with smp_list_del() at any position and smp_list_add/splice() at head position concurrently without taking any lock. This patch makes use of this technique on free list. To make this happen,

[RFC PATCH 7/9] mm: use read_lock for free path

Daniel Jordan's patch has made it possible for multiple threads to operate on a global list with smp_list_del() at any position and smp_list_add/splice() at head position concurrently without taking any lock. This patch makes use of this technique on free list. To make this happen,