[PATCH] mm/hugetlb: avoid looping to the same hugepage if !pages and

["tonnylu(陆志刚)" <tonnylu@tencent.com>]

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This change greatly decrease the time of mmaping a file in hugetlbfs.
With MAP_POPULATE flag, it takes about 50 milliseconds to mmap an
existing 128GB file in hugetlbfs. With this change, it takes less
then 1 millisecond.

Signed-off-by: Zhigang Lu <tonnylu@tencent.com>
Reviewed-by: Haozhong Zhang <hzhongzhang@tencent.com>
Reviewed-by: Zongming Zhang <knightzhang@tencent.com>
---
mm/hugetlb.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6d7296d..2df941a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4391,6 +4391,17 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
                          break;
                   }
            }
+
+            if (!pages && !vmas && !pfn_offset &&
+                (vaddr + huge_page_size(h) < vma->vm_end) &&
+                (remainder >= pages_per_huge_page(h))) {
+                   vaddr += huge_page_size(h);
+                   remainder -= pages_per_huge_page(h);
+                   i += pages_per_huge_page(h);
+                   spin_unlock(ptl);
+                   continue;
+            }
+
same_page:
            if (pages) {
                   pages[i] = mem_map_offset(page, pfn_offset);
--
1.8.3.1


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