The patch titled
Subject: mm/swap_state.c: simplify total_swapcache_pages() with get_swap_device()
has been added to the -mm tree. Its filename is
mm-swap-simplify-total_swapcache_pages-with-get_swap_device.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-swap-simplify-total_swapcache_pages-with-get_swap_device.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-swap-simplify-total_swapcache_pages-with-get_swap_device.patch
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------------------------------------------------------
From: Huang Ying <ying.huang@xxxxxxxxx>
Subject: 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.
Link: http://lkml.kernel.org/r/20190527082714.12151-1-ying.huang@xxxxxxxxx
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Cc: Andrea Parri <andrea.parri@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swap_state.c | 28 ++++++++++------------------
1 file changed, 10 insertions(+), 18 deletions(-)
--- a/mm/swap_state.c~mm-swap-simplify-total_swapcache_pages-with-get_swap_device
+++ a/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
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,
_
Patches currently in -mm which might be from ying.huang@xxxxxxxxx are
mm-swap-fix-race-between-swapoff-and-some-swap-operations.patch
mm-swap-simplify-total_swapcache_pages-with-get_swap_device.patch
