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>
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 8c66486..235c039 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -8,7 +8,7 @@
#include <linux/memcontrol.h>
#include <linux/sched.h>
#include <linux/node.h>
-
+#include <linux/fs.h>
#include <linux/atomic.h>
#include <asm/page.h>
@@ -330,8 +330,9 @@
sector_t *);
/* linux/mm/swap_state.c */
-extern struct address_space swapper_space;
-#define total_swapcache_pages swapper_space.nrpages
+extern struct address_space swapper_spaces[];
+#define swap_address_space(entry) (&swapper_spaces[swp_type(entry)])
+extern unsigned long total_swapcache_pages(void);
extern void show_swap_cache_info(void);
extern int add_to_swap(struct page *);
extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
@@ -382,7 +383,7 @@
#define nr_swap_pages 0L
#define total_swap_pages 0L
-#define total_swapcache_pages 0UL
+#define total_swapcache_pages() 0UL
#define si_swapinfo(val) \
do { (val)->freeswap = (val)->totalswap = 0; } while (0)