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From:   Feng Tang <feng.tang@intel.com>
To:     Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@suse.de>,
        Kees Cook <keescook@chromium.org>, Qian Cai <cai@lca.pw>,
        andi.kleen@intel.com, tim.c.chen@intel.com, dave.hansen@intel.com,
        ying.huang@intel.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Cc:     Feng Tang <feng.tang@intel.com>
Subject: [PATCH v4 2/4] mm/util.c: make vm_memory_committed() more accurate
Date:   Fri, 29 May 2020 09:06:08 +0800
Message-Id: <1590714370-67182-3-git-send-email-feng.tang@intel.com>
In-Reply-To: <1590714370-67182-1-git-send-email-feng.tang@intel.com>
References: <1590714370-67182-1-git-send-email-feng.tang@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

percpu_counter_sum_positive() will provide more accurate info.

As with percpu_counter_read_positive(), in worst case the deviation
could be 'batch * nr_cpus', which is totalram_pages/256 for now,
and will be more when the batch gets enlarged.

Its time cost is about 800 nanoseconds on a 2C/4T platform and
2~3 microseconds on a 2S/36C/72T server in normal case, and in
worst case where vm_committed_as's spinlock is under severe
contention, it costs 30~40 microseconds for the 2S/36C/72T sever,
which should be fine for its only two users: /proc/meminfo and
HyperV balloon driver's status trace per second.

Signed-off-by: Feng Tang <feng.tang@intel.com>
---
 mm/util.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/util.c b/mm/util.c
index 9b3be03..3c7a08c 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -790,7 +790,7 @@ struct percpu_counter vm_committed_as ____cacheline_aligned_in_smp;
  */
 unsigned long vm_memory_committed(void)
 {
-	return percpu_counter_read_positive(&vm_committed_as);
+	return percpu_counter_sum_positive(&vm_committed_as);
 }
 EXPORT_SYMBOL_GPL(vm_memory_committed);
 
-- 
2.7.4