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[192.55.52.93]) by mx.google.com with ESMTPS id r135si2993979pfc.123.2019.02.14.23.50.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 14 Feb 2019 23:50:26 -0800 (PST) Received-SPF: pass (google.com: domain of ying.huang@intel.com designates 192.55.52.93 as permitted sender) client-ip=192.55.52.93; Authentication-Results: mx.google.com; spf=pass (google.com: domain of ying.huang@intel.com designates 192.55.52.93 as permitted sender) smtp.mailfrom=ying.huang@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Feb 2019 23:50:26 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,372,1544515200"; d="scan'208";a="126685015" Received: from yhuang-dev.sh.intel.com (HELO yhuang-dev) ([10.239.159.151]) by orsmga003.jf.intel.com with ESMTP; 14 Feb 2019 23:50:23 -0800 From: "Huang\, Ying" To: Andrea Arcangeli Cc: Andrew Morton , , , Hugh Dickins , "Paul E . McKenney" , Minchan Kim , Johannes Weiner , Tim Chen , Mel Gorman , =?utf-8?Q?J=EF=BF=BDr=EF=BF=BDme_Glisse?= , Michal Hocko , David Rientjes , Rik van Riel , Jan Kara , Dave Jiang , Daniel Jordan , Andrea Parri Subject: Re: [PATCH -mm -V7] mm, swap: fix race between swapoff and some swap operations References: <20190211083846.18888-1-ying.huang@intel.com> <20190214023805.GA19090@redhat.com> <87k1i2oks6.fsf@yhuang-dev.intel.com> <20190214214741.GB10698@redhat.com> Date: Fri, 15 Feb 2019 15:50:21 +0800 In-Reply-To: <20190214214741.GB10698@redhat.com> (Andrea Arcangeli's message of "Thu, 14 Feb 2019 16:47:41 -0500") Message-ID: <87mumxa3sy.fsf@yhuang-dev.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii 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: Andrea Arcangeli writes: > On Thu, Feb 14, 2019 at 04:07:37PM +0800, Huang, Ying wrote: >> Before, we choose to use stop_machine() to reduce the overhead of hot >> path (page fault handler) as much as possible. But now, I found >> rcu_read_lock_sched() is just a wrapper of preempt_disable(). So maybe >> we can switch to RCU version now. > > rcu_read_lock looks more efficient than rcu_read_lock_sched. So for > this purpose in the fast path rcu_read_lock()/unlock() should be the > preferred methods, no need to force preempt_disable() (except for > debug purposes if sleep debug is enabled). Server builds are done with > voluntary preempt (no preempt shouldn't even exist as config option) > and there rcu_read_lock might be just a noop. If CONFIG_PREEMPT_VOLUNTARY=y CONFIG_PREEMPT=n CONFIG_PREEMPT_COUNT=n which is common for servers, rcu_read_lock() will be a noop, rcu_read_lock_sched() and preempt_disable() will be barrier(). So rcu_read_lock() is a little better. > Against a fast path rcu_read_lock/unlock before the consolidation > synchronize_rcu would have been enough, now after the consolidation > even more certain that it's enough because it's equivalent to _mult. Yes. Will change to rcu_read_lock/unlock based method. Best Regards, Huang, Ying