leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

mm/hugetlb: avoid looping to the same hugepage if !pages and !vmas

Browse Source 
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>
This commit is contained in:
Zhigang Lu 2019-11-30 17:57:06 -08:00 committed by Linus Torvalds
parent 188b04a7d9
commit acbfb087e3
1 changed files with 15 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
mm/hugetlb.c
View File

@ -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);