mm, thp: drop page_table_lock to uncharge memcg pages

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>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index edfeb8c..d0def42 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -973,8 +973,10 @@ 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));