mm/ksm: Remove now-redundant smp_read_barrier_depends()

Because READ_ONCE() now implies smp_read_barrier_depends(), the
smp_read_barrier_depends() in get_ksm_page() is now redundant.
This commit removes it and updates the comments.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Cc: <linux-mm@kvack.org>

diff --git a/mm/ksm.c b/mm/ksm.c
index be8f4576f84211499e269f4c69f993a975a8e0a9..c406f75957ad49c646c12559d8f2f58f4713a715 100644 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -675,15 +675,8 @@ static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
        expected_mapping = (void *)((unsigned long)stable_node |
                                        PAGE_MAPPING_KSM);
 again:
-       kpfn = READ_ONCE(stable_node->kpfn);
+       kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
        page = pfn_to_page(kpfn);
-
-       /*
-        * page is computed from kpfn, so on most architectures reading
-        * page->mapping is naturally ordered after reading node->kpfn,
-        * but on Alpha we need to be more careful.
-        */
-       smp_read_barrier_depends();
        if (READ_ONCE(page->mapping) != expected_mapping)
                goto stale;