[PATCH 1/1] mm: update min_free_kbytes from khugepaged after core initialization

[Jason Baron]

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.

Fixes: 79553da293d3 ("thp: cleanup khugepaged startup")
Signed-off-by: Jason Baron <jbaron@xxxxxxxxxx>
---
 mm/page_alloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 59de90d5d3a3..c1069efcc4d7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6485,7 +6485,7 @@ int __meminit init_per_zone_wmark_min(void)
 	setup_per_zone_inactive_ratio();
 	return 0;
 }
-module_init(init_per_zone_wmark_min)
+core_initcall(init_per_zone_wmark_min)
 
 /*
  * min_free_kbytes_sysctl_handler - just a wrapper around proc_dointvec() so
-- 
2.6.1