[patch] mm, thp: drop page_table_lock to uncharge memcg pages

[David Rientjes <rientjes@google.com>]

mm->page_table_lock is hotly contested for page fault tests and isn't
necessary to do mem_cgroup_uncharge_page() in do_huge_pmd_wp_page().

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/huge_memory.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -968,8 +968,10 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	spin_lock(&mm->page_table_lock);
 	put_page(page);
 	if (unlikely(!pmd_same(*pmd, orig_pmd))) {
+		spin_unlock(&mm->page_table_lock);
 		mem_cgroup_uncharge_page(new_page);
 		put_page(new_page);
+		goto out;
 	} else {
 		pmd_t entry;
 		VM_BUG_ON(!PageHead(page));

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