The scenario on which "Free swap -4kB" happens in my system, which is caused by get_swap_page_of_type or get_swap_pages racing with show_mem. Remove the race here.
Signed-off-by: Zhaoyang Huang <[email protected]> --- mm/swapfile.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index cf63b5f..13201b6 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -974,6 +974,8 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size) /* Only single cluster request supported */ WARN_ON_ONCE(n_goal > 1 && size == SWAPFILE_CLUSTER); + spin_lock(&swap_avail_lock); + avail_pgs = atomic_long_read(&nr_swap_pages) / size; if (avail_pgs <= 0) goto noswap; @@ -986,8 +988,6 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size) atomic_long_sub(n_goal * size, &nr_swap_pages); - spin_lock(&swap_avail_lock); - start_over: node = numa_node_id(); plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) { @@ -1061,14 +1061,13 @@ swp_entry_t get_swap_page_of_type(int type) spin_lock(&si->lock); if (si->flags & SWP_WRITEOK) { - atomic_long_dec(&nr_swap_pages); /* This is called for allocating swap entry, not cache */ offset = scan_swap_map(si, 1); if (offset) { + atomic_long_dec(&nr_swap_pages); spin_unlock(&si->lock); return swp_entry(type, offset); } - atomic_long_inc(&nr_swap_pages); } spin_unlock(&si->lock); fail: -- 1.9.1
