Commit 054f1d1f authored Jul 11, 2019 by Huang Ying Committed by Linus Torvalds Jul 12, 2019

mm/swap_state.c: simplify total_swapcache_pages() with get_swap_device()

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.

[ying.huang@intel.com: fix bad swap file entry warning]
  Link: http://lkml.kernel.org/r/20190531024102.21723-1-ying.huang@intel.com
Link: http://lkml.kernel.org/r/20190527082714.12151-1-ying.huang@intel.com


Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent eb085574

mm/swap_state.c

+15 −18

Original line number	Diff line number	Diff line
		@@ -73,23 +73,24 @@ 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)
		swp_entry_t entry = swp_entry(i, 1);

		/* Avoid get_swap_device() to warn for bad swap entry */
		if (!swp_swap_info(entry))
		continue;
		/* Prevent swapoff to free swapper_spaces */
		si = get_swap_device(entry);
		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 +612,16 @@ 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,

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