diff options
author | Zhigang Lu <tonnylu@tencent.com> | 2019-12-01 04:57:06 +0300 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-12-01 23:59:08 +0300 |
commit | acbfb087e3b19959d6f4b779a9a15bff644b8c9a (patch) | |
tree | b0786d716ffabb9701cb654810f55e1c2fc0f6a3 | |
parent | 188b04a7d93860fd100b2671600b8ad81fb0a842 (diff) |
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@gmail.com
Signed-off-by: Zhigang Lu <tonnylu@tencent.com>
Reviewed-by: Haozhong Zhang <hzhongzhang@tencent.com>
Reviewed-by: Zongming Zhang <knightzhang@tencent.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | mm/hugetlb.c | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 8624b7758abb..ac65bb5e38ac 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4338,6 +4338,21 @@ 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); |