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[134.134.136.20]) by mx.google.com with ESMTPS id g129si18580850pfb.181.2019.05.27.01.27.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 27 May 2019 01:27:22 -0700 (PDT) Received-SPF: pass (google.com: domain of ying.huang@intel.com designates 134.134.136.20 as permitted sender) client-ip=134.134.136.20; Authentication-Results: mx.google.com; spf=pass (google.com: domain of ying.huang@intel.com designates 134.134.136.20 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 fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 May 2019 01:27:21 -0700 X-ExtLoop1: 1 Received: from yhuang-dev.sh.intel.com ([10.239.159.29]) by fmsmga001.fm.intel.com with ESMTP; 27 May 2019 01:27:18 -0700 From: "Huang, Ying" To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Huang Ying , Hugh Dickins , "Paul E . McKenney" , Minchan Kim , Johannes Weiner , Tim Chen , Mel Gorman , =?utf-8?b?SsOpcsO0bWUgR2xpc3Nl?= , Michal Hocko , Andrea Arcangeli , Yang Shi , David Rientjes , Rik van Riel , Jan Kara , Dave Jiang , Daniel Jordan , Andrea Parri Subject: [PATCH -mm] mm, swap: Simplify total_swapcache_pages() with get_swap_device() Date: Mon, 27 May 2019 16:27:14 +0800 Message-Id: <20190527082714.12151-1-ying.huang@intel.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 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: X-Virus-Scanned: ClamAV using ClamSMTP 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. Signed-off-by: "Huang, Ying" Cc: Hugh Dickins Cc: Paul E. McKenney Cc: Minchan Kim Cc: Johannes Weiner Cc: Tim Chen Cc: Mel Gorman Cc: Jérôme Glisse Cc: Michal Hocko Cc: Andrea Arcangeli Cc: Yang Shi Cc: David Rientjes Cc: Rik van Riel Cc: Jan Kara Cc: Dave Jiang Cc: Daniel Jordan Cc: Andrea Parri --- mm/swap_state.c | 28 ++++++++++------------------ 1 file changed, 10 insertions(+), 18 deletions(-) diff --git a/mm/swap_state.c b/mm/swap_state.c index f509cdaa81b1..b84c58b572ca 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -73,23 +73,19 @@ unsigned long total_swapcache_pages(void) unsigned int i, j, nr; unsigned long ret = 0; struct address_space *spaces; + struct swap_info_struct *si; - rcu_read_lock(); for (i = 0; i < MAX_SWAPFILES; i++) { - /* - * The corresponding entries in nr_swapper_spaces and - * swapper_spaces will be reused only after at least - * one grace period. So it is impossible for them - * belongs to different usage. - */ - nr = nr_swapper_spaces[i]; - spaces = rcu_dereference(swapper_spaces[i]); - if (!nr || !spaces) + /* Prevent swapoff to free swapper_spaces */ + si = get_swap_device(swp_entry(i, 1)); + if (!si) continue; + nr = nr_swapper_spaces[i]; + spaces = swapper_spaces[i]; for (j = 0; j < nr; j++) ret += spaces[j].nrpages; + put_swap_device(si); } - rcu_read_unlock(); return ret; } @@ -611,20 +607,16 @@ int init_swap_address_space(unsigned int type, unsigned long nr_pages) mapping_set_no_writeback_tags(space); } nr_swapper_spaces[type] = nr; - rcu_assign_pointer(swapper_spaces[type], spaces); + swapper_spaces[type] = spaces; return 0; } void exit_swap_address_space(unsigned int type) { - struct address_space *spaces; - - spaces = swapper_spaces[type]; + kvfree(swapper_spaces[type]); nr_swapper_spaces[type] = 0; - rcu_assign_pointer(swapper_spaces[type], NULL); - synchronize_rcu(); - kvfree(spaces); + swapper_spaces[type] = NULL; } static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,