* [PATCH tip/core/rcu 13/21] mm/ksm: Remove now-redundant smp_read_barrier_depends()
[not found] <20171201195053.GA23494@linux.vnet.ibm.com>
@ 2017-12-01 19:51 ` Paul E. McKenney
0 siblings, 0 replies; only message in thread
From: Paul E. McKenney @ 2017-12-01 19:51 UTC (permalink / raw)
To: linux-kernel
Cc: mingo, jiangshanlai, dipankar, akpm, mathieu.desnoyers, josh,
tglx, peterz, rostedt, dhowells, edumazet, fweisbec, oleg,
Paul E. McKenney, Andrea Arcangeli, Minchan Kim, Michal Hocko,
Kirill A. Shutemov, Aneesh Kumar K.V, Claudio Imbrenda, linux-mm
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>
---
mm/ksm.c | 9 +--------
1 file changed, 1 insertion(+), 8 deletions(-)
diff --git a/mm/ksm.c b/mm/ksm.c
index be8f4576f842..c406f75957ad 100644
--- 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;
--
2.5.2
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