From: Zhigang Lu <tonnylu@xxxxxxxxxxx>
When mmapping an existing hugetlbfs file with MAP_POPULATE, we find
it is very time consuming. For example, mmapping a 128GB file takes
about 50 milliseconds. Sampling with perfevent shows it spends 99%
time in the same_page loop in follow_hugetlb_page().
samples: 205 of event 'cycles', Event count (approx.): 136686374
- 99.04% test_mmap_huget [kernel.kallsyms] [k] follow_hugetlb_page
follow_hugetlb_page
__get_user_pages
__mlock_vma_pages_range
__mm_populate
vm_mmap_pgoff
sys_mmap_pgoff
sys_mmap
system_call_fastpath
__mmap64
follow_hugetlb_page() is called with pages=NULL and vmas=NULL, so for
each hugepage, we run into the same_page loop for pages_per_huge_page()
times, but doing nothing. With this change, it takes less then 1
millisecond to mmap a 128GB file in hugetlbfs.
Signed-off-by: Zhigang Lu <tonnylu@xxxxxxxxxxx>
Reviewed-by: Haozhong Zhang <hzhongzhang@xxxxxxxxxxx>
Reviewed-by: Zongming Zhang <knightzhang@xxxxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Acked-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
---
mm/hugetlb.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6d7296d..a096fb3 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4391,6 +4391,21 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
break;
}
}
+
+ /*
+ * If subpage information not requested, update counters
+ * and skip the same_page loop below.
+ */
+ 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
