From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757332Ab0EELWO (ORCPT ); Wed, 5 May 2010 07:22:14 -0400 Received: from smtp.nokia.com ([192.100.122.230]:18350 "EHLO mgw-mx03.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755224Ab0EELWM (ORCPT ); Wed, 5 May 2010 07:22:12 -0400 From: Phil Carmody To: balbir@linux.vnet.ibm.com, nishimura@mxp.nes.nec.co.jp, kamezawa.hiroyu@jp.fujitsu.com Cc: akpm@linux-foundation.org, kirill@shutemov.name, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/2] mm: remove unnecessary use of atomic Date: Wed, 5 May 2010 14:21:48 +0300 Message-Id: <1273058509-16625-1-git-send-email-ext-phil.2.carmody@nokia.com> X-Mailer: git-send-email 1.6.0.4 X-OriginalArrivalTime: 05 May 2010 11:21:34.0439 (UTC) FILETIME=[1EA32F70:01CAEC45] X-Nokia-AV: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Phil Carmody The bottom 4 hunks are atomically changing memory to which there are no aliases as it's freshly allocated, so there's no need to use atomic operations. The other hunks are just atomic_read and atomic_set, and do not involve any read-modify-write. The use of atomic_{read,set} doesn't prevent a read/write or write/write race, so if a race were possible (I'm not saying one is), then it would still be there even with atomic_set. See: http://digitalvampire.org/blog/index.php/2007/05/13/atomic-cargo-cults/ Signed-off-by: Phil Carmody Acked-by: Kirill A. Shutemov --- mm/memcontrol.c | 14 +++++++------- 1 files changed, 7 insertions(+), 7 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6c755de..90e32b2 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -151,7 +151,7 @@ struct mem_cgroup_threshold { struct mem_cgroup_threshold_ary { /* An array index points to threshold just below usage. */ - atomic_t current_threshold; + int current_threshold; /* Size of entries[] */ unsigned int size; /* Array of thresholds */ @@ -3327,7 +3327,7 @@ static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap) * If it's not true, a threshold was crossed after last * call of __mem_cgroup_threshold(). */ - i = atomic_read(&t->current_threshold); + i = t->current_threshold; /* * Iterate backward over array of thresholds starting from @@ -3351,7 +3351,7 @@ static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap) eventfd_signal(t->entries[i].eventfd, 1); /* Update current_threshold */ - atomic_set(&t->current_threshold, i - 1); + t->current_threshold = i - 1; unlock: rcu_read_unlock(); } @@ -3429,7 +3429,7 @@ static int mem_cgroup_register_event(struct cgroup *cgrp, struct cftype *cft, compare_thresholds, NULL); /* Find current threshold */ - atomic_set(&thresholds_new->current_threshold, -1); + thresholds_new->current_threshold = -1; for (i = 0; i < size; i++) { if (thresholds_new->entries[i].threshold < usage) { /* @@ -3437,7 +3437,7 @@ static int mem_cgroup_register_event(struct cgroup *cgrp, struct cftype *cft, * until rcu_assign_pointer(), so it's safe to increment * it here. */ - atomic_inc(&thresholds_new->current_threshold); + ++thresholds_new->current_threshold; } } @@ -3508,7 +3508,7 @@ static int mem_cgroup_unregister_event(struct cgroup *cgrp, struct cftype *cft, thresholds_new->size = size; /* Copy thresholds and find current threshold */ - atomic_set(&thresholds_new->current_threshold, -1); + thresholds_new->current_threshold = -1; for (i = 0, j = 0; i < thresholds->size; i++) { if (thresholds->entries[i].eventfd == eventfd) continue; @@ -3520,7 +3520,7 @@ static int mem_cgroup_unregister_event(struct cgroup *cgrp, struct cftype *cft, * until rcu_assign_pointer(), so it's safe to increment * it here. */ - atomic_inc(&thresholds_new->current_threshold); + ++thresholds_new->current_threshold; } j++; } -- 1.6.0.4