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frontswap: make frontswap_init use a pointer for the ops

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This simplifies the code in the frontswap - we can get rid of the
'backend_registered' test and instead check against frontswap_ops.

[v1: Rebase on top of 703ba7fe5e (ramster->zcache move]
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by: Bob Liu <[email protected]>
Cc: Wanpeng Li <[email protected]>
Cc: Andor Daam <[email protected]>
Cc: Dan Magenheimer <[email protected]>
Cc: Florian Schmaus <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Stefan Hengelein <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Konrad Rzeszutek Wilk 2013-04-30 15:26:51 -07:00 • committed by Linus Torvalds
commit 1e01c968db
4 changed files with 26 additions and 28 deletions
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38
mm/frontswap.c
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@ -24,7 +24,7 @@
* frontswap_ops is set by frontswap_register_ops to contain the pointers
* to the frontswap "backend" implementation functions.
*/
static struct frontswap_ops frontswap_ops __read_mostly;
static struct frontswap_ops *frontswap_ops __read_mostly;
/*
* This global enablement flag reduces overhead on systems where frontswap_ops
@ -108,41 +108,39 @@ static inline void inc_frontswap_invalidates(void) { }
*
* The time between the backend being registered and the swap file system
* calling the backend (via the frontswap_* functions) is indeterminate as
* backend_registered is not atomic_t (or a value guarded by a spinlock).
* frontswap_ops is not atomic_t (or a value guarded by a spinlock).
* That is OK as we are comfortable missing some of these calls to the newly
* registered backend.
*
* Obviously the opposite (unloading the backend) must be done after all
* the frontswap_[store|load|invalidate_area|invalidate_page] start
* ignorning or failing the requests - at which point backend_registered
* ignorning or failing the requests - at which point frontswap_ops
* would have to be made in some fashion atomic.
*/
static DECLARE_BITMAP(need_init, MAX_SWAPFILES);
static bool backend_registered __read_mostly;
/*
* Register operations for frontswap, returning previous thus allowing
* detection of multiple backends and possible nesting.
*/
struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
struct frontswap_ops *frontswap_register_ops(struct frontswap_ops *ops)
{
struct frontswap_ops old = frontswap_ops;
struct frontswap_ops *old = frontswap_ops;
int i;
frontswap_ops = *ops;
frontswap_enabled = true;
for (i = 0; i < MAX_SWAPFILES; i++) {
if (test_and_clear_bit(i, need_init))
(*frontswap_ops.init)(i);
ops->init(i);
}
/*
* We MUST have backend_registered set _after_ the frontswap_init's
* We MUST have frontswap_ops set _after_ the frontswap_init's
* have been called. Otherwise __frontswap_store might fail. Hence
* the barrier to make sure compiler does not re-order us.
*/
barrier();
backend_registered = true;
frontswap_ops = ops;
return old;
}
EXPORT_SYMBOL(frontswap_register_ops);
@ -172,11 +170,11 @@ void __frontswap_init(unsigned type)
{
struct swap_info_struct *sis = swap_info[type];
if (backend_registered) {
if (frontswap_ops) {
BUG_ON(sis == NULL);
if (sis->frontswap_map == NULL)
return;
(*frontswap_ops.init)(type);
frontswap_ops->init(type);
} else {
BUG_ON(type > MAX_SWAPFILES);
set_bit(type, need_init);
@ -206,7 +204,7 @@ int __frontswap_store(struct page *page)
struct swap_info_struct *sis = swap_info[type];
pgoff_t offset = swp_offset(entry);
if (!backend_registered) {
if (!frontswap_ops) {
inc_frontswap_failed_stores();
return ret;
}
@ -215,7 +213,7 @@ int __frontswap_store(struct page *page)
BUG_ON(sis == NULL);
if (frontswap_test(sis, offset))
dup = 1;
ret = frontswap_ops.store(type, offset, page);
ret = frontswap_ops->store(type, offset, page);
if (ret == 0) {
frontswap_set(sis, offset);
inc_frontswap_succ_stores();
@ -250,13 +248,13 @@ int __frontswap_load(struct page *page)
struct swap_info_struct *sis = swap_info[type];
pgoff_t offset = swp_offset(entry);
if (!backend_registered)
if (!frontswap_ops)
return ret;
BUG_ON(!PageLocked(page));
BUG_ON(sis == NULL);
if (frontswap_test(sis, offset))
ret = frontswap_ops.load(type, offset, page);
ret = frontswap_ops->load(type, offset, page);
if (ret == 0) {
inc_frontswap_loads();
if (frontswap_tmem_exclusive_gets_enabled) {
@ -276,12 +274,12 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
{
struct swap_info_struct *sis = swap_info[type];
if (!backend_registered)
if (!frontswap_ops)
return;
BUG_ON(sis == NULL);
if (frontswap_test(sis, offset)) {
frontswap_ops.invalidate_page(type, offset);
frontswap_ops->invalidate_page(type, offset);
__frontswap_clear(sis, offset);
inc_frontswap_invalidates();
}
@ -296,11 +294,11 @@ void __frontswap_invalidate_area(unsigned type)
{
struct swap_info_struct *sis = swap_info[type];
if (backend_registered) {
if (frontswap_ops) {
BUG_ON(sis == NULL);
if (sis->frontswap_map == NULL)
return;
(*frontswap_ops.invalidate_area)(type);
frontswap_ops->invalidate_area(type);
atomic_set(&sis->frontswap_pages, 0);
memset(sis->frontswap_map, 0, sis->max / sizeof(long));
}