[PATCH] swap: swap_lock replace list+device
The idea of a swap_device_lock per device, and a swap_list_lock over them all,
is appealing; but in practice almost every holder of swap_device_lock must
already hold swap_list_lock, which defeats the purpose of the split.
The only exceptions have been swap_duplicate, valid_swaphandles and an
untrodden path in try_to_unuse (plus a few places added in this series).
valid_swaphandles doesn't show up high in profiles, but swap_duplicate does
demand attention. However, with the hold time in get_swap_pages so much
reduced, I've not yet found a load and set of swap device priorities to show
even swap_duplicate benefitting from the split. Certainly the split is mere
overhead in the common case of a single swap device.
So, replace swap_list_lock and swap_device_lock by spinlock_t swap_lock
(generally we seem to prefer an _ in the name, and not hide in a macro).
If someone can show a regression in swap_duplicate, then probably we should
add a hashlock for the swap_map entries alone (shorts being anatomic), so as
to help the case of the single swap device too.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/swap.h b/include/linux/swap.h
index db3b5de..3c9ff00 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -121,7 +121,7 @@
*/
struct swap_info_struct {
unsigned int flags;
- spinlock_t sdev_lock;
+ int prio; /* swap priority */
struct file *swap_file;
struct block_device *bdev;
struct list_head extent_list;
@@ -135,7 +135,6 @@
unsigned int pages;
unsigned int max;
unsigned int inuse_pages;
- int prio; /* swap priority */
int next; /* next entry on swap list */
};
@@ -221,13 +220,7 @@
extern int remove_exclusive_swap_page(struct page *);
struct backing_dev_info;
-extern struct swap_list_t swap_list;
-extern spinlock_t swaplock;
-
-#define swap_list_lock() spin_lock(&swaplock)
-#define swap_list_unlock() spin_unlock(&swaplock)
-#define swap_device_lock(p) spin_lock(&p->sdev_lock)
-#define swap_device_unlock(p) spin_unlock(&p->sdev_lock)
+extern spinlock_t swap_lock;
/* linux/mm/thrash.c */
extern struct mm_struct * swap_token_mm;