From: Zhigang Lu <tonnylu@xxxxxxxxxxx>
Subject: mm/hugetlb: avoid looping to the same hugepage if !pages and !vmas
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.
Link: http://lkml.kernel.org/r/1567581712-5992-1-git-send-email-totty.lu@xxxxxxxxx
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>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
--- a/mm/hugetlb.c~mm-hugetlb-avoid-looping-to-the-same-hugepage-if-pages-and-vmas
+++ a/mm/hugetlb.c
@@ -4338,6 +4338,21 @@ long follow_hugetlb_page(struct mm_struc
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);
_
