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authorZhigang Lu <tonnylu@tencent.com>2019-11-30 17:57:06 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-12-01 12:59:08 -0800
commitacbfb087e3b19959d6f4b779a9a15bff644b8c9a (patch)
treeb0786d716ffabb9701cb654810f55e1c2fc0f6a3 /mm
parent188b04a7d93860fd100b2671600b8ad81fb0a842 (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>
Diffstat (limited to 'mm')
-rw-r--r--mm/hugetlb.c15
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);