swap: make each swap partition have one address_space

When I use several fast SSD to do swap, swapper_space.tree_lock is
heavily contended.  This makes each swap partition have one
address_space to reduce the lock contention.  There is an array of
address_space for swap.  The swap entry type is the index to the array.

In my test with 3 SSD, this increases the swapout throughput 20%.

[akpm@linux-foundation.org: revert unneeded change to  __add_to_swap_cache]
Signed-off-by: Shaohua Li <shli@fusionio.com>
Cc: Hugh Dickins <hughd@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
index c3dac611c3c0..1efaaa19c4f3 100644
--- a/fs/proc/meminfo.c
+++ b/fs/proc/meminfo.c
@@ -40,7 +40,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
                 * sysctl_overcommit_ratio / 100) + total_swap_pages;
 
         cached = global_page_state(NR_FILE_PAGES) -
-                        total_swapcache_pages - i.bufferram;
+                        total_swapcache_pages() - i.bufferram;
         if (cached < 0)
                 cached = 0;
 
@@ -109,7 +109,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
                 K(i.freeram),
                 K(i.bufferram),
                 K(cached),
-                K(total_swapcache_pages),
+                K(total_swapcache_pages()),
                 K(pages[LRU_ACTIVE_ANON]   + pages[LRU_ACTIVE_FILE]),
                 K(pages[LRU_INACTIVE_ANON] + pages[LRU_INACTIVE_FILE]),
                 K(pages[LRU_ACTIVE_ANON]),