[patch 04/13] mm: huge_memory: use GFP_TRANSHUGE when charging huge pages

[Johannes Weiner <hannes@cmpxchg.org>]

Transparent huge page charges prefer falling back to regular pages
rather than spending a lot of time in direct reclaim.

Desired reclaim behavior is usually declared in the gfp mask, but THP
charges use GFP_KERNEL and then rely on the fact that OOM is disabled
for THP charges, and that OOM-disabled charges don't retry reclaim.
Needless to say, this is anything but obvious and quite error prone.

Convert THP charges to use GFP_TRANSHUGE instead, which implies
__GFP_NORETRY, to indicate the low-latency requirement.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
---
 mm/huge_memory.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e60837dc785c..10cd7f2bf776 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -827,7 +827,7 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		count_vm_event(THP_FAULT_FALLBACK);
 		return VM_FAULT_FALLBACK;
 	}
-	if (unlikely(mem_cgroup_charge_anon(page, mm, GFP_KERNEL))) {
+	if (unlikely(mem_cgroup_charge_anon(page, mm, GFP_TRANSHUGE))) {
 		put_page(page);
 		count_vm_event(THP_FAULT_FALLBACK);
 		return VM_FAULT_FALLBACK;
@@ -1101,7 +1101,7 @@ alloc:
 		goto out;
 	}
 
-	if (unlikely(mem_cgroup_charge_anon(new_page, mm, GFP_KERNEL))) {
+	if (unlikely(mem_cgroup_charge_anon(new_page, mm, GFP_TRANSHUGE))) {
 		put_page(new_page);
 		if (page) {
 			split_huge_page(page);
@@ -2368,7 +2368,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 	if (!new_page)
 		return;
 
-	if (unlikely(mem_cgroup_charge_anon(new_page, mm, GFP_KERNEL)))
+	if (unlikely(mem_cgroup_charge_anon(new_page, mm, GFP_TRANSHUGE)))
 		return;
 
 	/*
-- 
2.0.0