[patch] mm, thp: count thp_fault_fallback anytime thp fault fails

[David Rientjes <rientjes@google.com>]

Currently, thp_fault_fallback in vmstat only gets incremented if a
hugepage allocation fails.  If current's memcg hits its limit or the page
fault handler returns an error, it is incorrectly accounted as a
successful thp_fault_alloc.

Count thp_fault_fallback anytime the page fault handler falls back to
using regular pages and only count thp_fault_alloc when a hugepage has
actually been faulted.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/huge_memory.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -801,7 +801,6 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			zero_page = get_huge_zero_page();
 			if (unlikely(!zero_page)) {
 				pte_free(mm, pgtable);
-				count_vm_event(THP_FAULT_FALLBACK);
 				goto out;
 			}
 			spin_lock(&mm->page_table_lock);
@@ -816,11 +815,8 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		}
 		page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
 					  vma, haddr, numa_node_id(), 0);
-		if (unlikely(!page)) {
-			count_vm_event(THP_FAULT_FALLBACK);
+		if (unlikely(!page))
 			goto out;
-		}
-		count_vm_event(THP_FAULT_ALLOC);
 		if (unlikely(mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))) {
 			put_page(page);
 			goto out;
@@ -832,9 +828,11 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			goto out;
 		}
 
+		count_vm_event(THP_FAULT_ALLOC);
 		return 0;
 	}
 out:
+	count_vm_event(THP_FAULT_FALLBACK);
 	/*
 	 * Use __pte_alloc instead of pte_alloc_map, because we can't
 	 * run pte_offset_map on the pmd, if an huge pmd could

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