From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752434AbdLATx4 (ORCPT ); Fri, 1 Dec 2017 14:53:56 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:46806 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752227AbdLATv1 (ORCPT ); Fri, 1 Dec 2017 14:51:27 -0500 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, "Paul E. McKenney" , Andrea Arcangeli , Minchan Kim , Michal Hocko , "Kirill A. Shutemov" , "Aneesh Kumar K.V" , Claudio Imbrenda , Subject: [PATCH tip/core/rcu 13/21] mm/ksm: Remove now-redundant smp_read_barrier_depends() Date: Fri, 1 Dec 2017 11:51:08 -0800 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20171201195053.GA23494@linux.vnet.ibm.com> References: <20171201195053.GA23494@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17120119-0044-0000-0000-000003B83696 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008137; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000243; SDB=6.00953999; UDB=6.00482085; IPR=6.00734075; BA=6.00005726; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00018295; XFM=3.00000015; UTC=2017-12-01 19:51:23 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17120119-0045-0000-0000-000007E76793 Message-Id: <1512157876-24665-13-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-12-01_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1712010232 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: Andrew Morton Cc: Andrea Arcangeli Cc: Minchan Kim Cc: Michal Hocko Cc: "Kirill A. Shutemov" Cc: Ingo Molnar Cc: "Aneesh Kumar K.V" Cc: Claudio Imbrenda Cc: --- 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