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[37.188.178.109]) by smtp.gmail.com with ESMTPSA id z3sm1135456ejl.38.2020.06.03.06.35.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Jun 2020 06:35:29 -0700 (PDT) Date: Wed, 3 Jun 2020 15:35:28 +0200 From: Michal Hocko To: Feng Tang Cc: Andrew Morton , Johannes Weiner , Matthew Wilcox , Mel Gorman , Kees Cook , Qian Cai , 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, "K. Y. Srinivasan" , Haiyang Zhang Subject: Re: [PATCH v4 2/4] mm/util.c: make vm_memory_committed() more accurate Message-ID: <20200603133528.GJ7533@dhcp22.suse.cz> References: <1590714370-67182-1-git-send-email-feng.tang@intel.com> <1590714370-67182-3-git-send-email-feng.tang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1590714370-67182-3-git-send-email-feng.tang@intel.com> X-Rspamd-Queue-Id: 3A05810057575 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri 29-05-20 09:06:08, Feng Tang wrote: > 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 I cannot speak for HyperV part. Cc maintainers but this shouldn't be a problem for meminfo. Acked-by: Michal Hocko > --- > 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 > -- Michal Hocko SUSE Labs