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[PATCH] swap: swap_lock replace list+device

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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>
This commit is contained in:
Hugh Dickins
2005-09-03 15:54:41 -07:00
committed by Linus Torvalds
parent 048c27fd72
commit 5d337b9194
5 changed files with 70 additions and 99 deletions
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11
include/linux/swap.h
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@ -121,7 +121,7 @@ enum {
*/
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 @@ struct swap_info_struct {
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 can_share_swap_page(struct page *);
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;