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[134.134.136.24]) by mx.google.com with ESMTPS id t1si18835036plr.74.2019.05.27.17.46.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 27 May 2019 17:46:12 -0700 (PDT) Received-SPF: pass (google.com: domain of ying.huang@intel.com designates 134.134.136.24 as permitted sender) client-ip=134.134.136.24; Authentication-Results: mx.google.com; spf=pass (google.com: domain of ying.huang@intel.com designates 134.134.136.24 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 fmsmga007.fm.intel.com ([10.253.24.52]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 May 2019 17:46:12 -0700 X-ExtLoop1: 1 Received: from yhuang-dev.sh.intel.com (HELO yhuang-dev) ([10.239.159.29]) by fmsmga007.fm.intel.com with ESMTP; 27 May 2019 17:46:09 -0700 From: "Huang\, Ying" To: "Paul E. McKenney" Cc: Andrew Morton , , , Hugh Dickins , Minchan Kim , Johannes Weiner , Tim Chen , Mel Gorman , Jérôme Glisse , Michal Hocko , Andrea Arcangeli , Yang Shi , David Rientjes , "Rik van Riel" , Jan Kara , Dave Jiang , Daniel Jordan , "Andrea Parri" Subject: Re: [PATCH -mm] mm, swap: Simplify total_swapcache_pages() with get_swap_device() References: <20190527082714.12151-1-ying.huang@intel.com> <20190527101536.GI28207@linux.ibm.com> Date: Tue, 28 May 2019 08:46:02 +0800 In-Reply-To: <20190527101536.GI28207@linux.ibm.com> (Paul E. McKenney's message of "Mon, 27 May 2019 03:15:36 -0700") Message-ID: <871s0j8kz9.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: Hi, Paul, "Paul E. McKenney" writes: > On Mon, May 27, 2019 at 04:27:14PM +0800, Huang, Ying wrote: >> From: Huang Ying >> >> total_swapcache_pages() may race with swapper_spaces[] allocation and >> freeing. Previously, this is protected with a swapper_spaces[] >> specific RCU mechanism. To simplify the logic/code complexity, it is >> replaced with get/put_swap_device(). The code line number is reduced >> too. Although not so important, the swapoff() performance improves >> too because one synchronize_rcu() call during swapoff() is deleted. > > I am guessing that total_swapcache_pages() is not used on any > fastpaths, but must defer to others on this. Of course, if the > performance/scalability of total_swapcache_pages() is important, > benchmarking is needed. This patch is mostly about code cleanup instead of performance. That is, to make the code easier to be understand. > But where do I find get_swap_device() and put_swap_device()? I do not > see them in current mainline. They are not in mainline, but in -mm tree. I should have made it more clear. Sorry about that. Best Regards, Huang, Ying