mm: update min_free_kbytes from khugepaged after core initialization

Khugepaged attempts to raise min_free_kbytes if its set too low. However, on boot khugepaged sets min_free_kbytes first from subsys_initcall(), and then the mm 'core' over-rides min_free_kbytes after from init_per_zone_wmark_min(), via a module_init() call. Khugepaged used to use a late_initcall() to set min_free_kbytes (such that it occurred after the core initialization), however this was removed when the initialization of min_free_kbytes was integrated into the starting of the khugepaged thread. The fix here is simply to invoke the core initialization using a core_initcall() instead of module_init(), such that the previous initialization ordering is restored. I didn't restore the late_initcall() since start_stop_khugepaged() already sets min_free_kbytes via set_recommended_min_free_kbytes(). This was noticed when we had a number of page allocation failures when moving a workload to a kernel with this new initialization ordering. On an 8GB system this restores min_free_kbytes back to 67584 from 11365 when CONFIG_TRANSPARENT_HUGEPAGE=y is set and either CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y or CONFIG_TRANSPARENT_HUGEPAGE_MADVISE=y.

JBJason Baron committed 10 years ago