mm/khugepaged.c: replace barrier() with READ_ONCE() for a selective variable

READ_ONCE() is more selective and lightweight.  It is more appropriate
that using a READ_ONCE() for the certain variable to prevent the
compiler from reordering.

Link: https://lkml.kernel.org/r/20210323092730.247583-1-yanfei.xu@windriver.com
Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index adf6772..a40a294 100644 (file)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2202,11 +2202,9 @@ static void khugepaged_do_scan(void)
 {
        struct page *hpage = NULL;
        unsigned int progress = 0, pass_through_head = 0;
-       unsigned int pages = khugepaged_pages_to_scan;
+       unsigned int pages = READ_ONCE(khugepaged_pages_to_scan);
        bool wait = true;
 
-       barrier(); /* write khugepaged_pages_to_scan to local stack */
-
        lru_add_drain_all();
 
        while (progress < pages) {