add sysfs: nr_max_batched_migration
add drop_caches before make test. use vmalloc as the migrate_buffer. size of migrate_buffer is now alterable
migrate_list is used now.
iterate over migrate_list to read the segment data
refactor and impl migrate_linked_segments. nr_mig=1 constant is tested
nr_mig > 1 tested. maybe this branch should close
Merge branch 'feature/batched-migration' into develop