Commit 8ea1d2a1 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
Browse files

mm, frontswap: convert frontswap_enabled to static key

I have noticed that frontswap.h first declares "frontswap_enabled" as
extern bool variable, and then overrides it with "#define
frontswap_enabled (1)" for CONFIG_FRONTSWAP=Y or (0) when disabled.  The
bool variable isn't actually instantiated anywhere.

This all looks like an unfinished attempt to make frontswap_enabled
reflect whether a backend is instantiated.  But in the current state,
all frontswap hooks call unconditionally into frontswap.c just to check
if frontswap_ops is non-NULL.  This should at least be checked inline,
but we can further eliminate the overhead when CONFIG_FRONTSWAP is
enabled and no backend registered, using a static key that is initially
disabled, and gets enabled only upon first backend registration.

Thus, checks for "frontswap_enabled" are replaced with
"frontswap_enabled()" wrapping the static key check.  There are two
exceptions:

- xen's selfballoon_process() was testing frontswap_enabled in code guarded
  by #ifdef C...
parent fbe84a09
......@@ -195,7 +195,7 @@ static void selfballoon_process(struct work_struct *work)
MB2PAGES(selfballoon_reserved_mb);
#ifdef CONFIG_FRONTSWAP
/* allow space for frontswap pages to be repatriated */
if (frontswap_selfshrinking && frontswap_enabled)
if (frontswap_selfshrinking)
goal_pages += frontswap_curr_pages();
#endif
if (cur_pages > goal_pages)
......@@ -230,7 +230,7 @@ static void selfballoon_process(struct work_struct *work)
reset_timer = true;
}
#ifdef CONFIG_FRONTSWAP
if (frontswap_selfshrinking && frontswap_enabled) {
if (frontswap_selfshrinking) {
frontswap_selfshrink();
reset_timer = true;
}
......
......@@ -4,6 +4,7 @@
#include <linux/swap.h>
#include <linux/mm.h>
#include <linux/bitops.h>
#include <linux/jump_label.h>
struct frontswap_ops {
void (*init)(unsigned); /* this swap type was just swapon'ed */
......@@ -14,7 +15,6 @@ struct frontswap_ops {
struct frontswap_ops *next; /* private pointer to next ops */
};
extern bool frontswap_enabled;
extern void frontswap_register_ops(struct frontswap_ops *ops);
extern void frontswap_shrink(unsigned long);
extern unsigned long frontswap_curr_pages(void);
......@@ -30,7 +30,12 @@ extern void __frontswap_invalidate_page(unsigned, pgoff_t);
extern void __frontswap_invalidate_area(unsigned);
#ifdef CONFIG_FRONTSWAP
#define frontswap_enabled (1)
extern struct static_key_false frontswap_enabled_key;
static inline bool frontswap_enabled(void)
{
return static_branch_unlikely(&frontswap_enabled_key);
}
static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
{
......@@ -50,7 +55,10 @@ static inline unsigned long *frontswap_map_get(struct swap_info_struct *p)
#else
/* all inline routines become no-ops and all externs are ignored */
#define frontswap_enabled (0)
static inline bool frontswap_enabled(void)
{
return false;
}
static inline bool frontswap_test(struct swap_info_struct *sis, pgoff_t offset)
{
......@@ -70,37 +78,35 @@ static inline unsigned long *frontswap_map_get(struct swap_info_struct *p)
static inline int frontswap_store(struct page *page)
{
int ret = -1;
if (frontswap_enabled())
return __frontswap_store(page);
if (frontswap_enabled)
ret = __frontswap_store(page);
return ret;
return -1;
}
static inline int frontswap_load(struct page *page)
{
int ret = -1;
if (frontswap_enabled())
return __frontswap_load(page);
if (frontswap_enabled)
ret = __frontswap_load(page);
return ret;
return -1;
}
static inline void frontswap_invalidate_page(unsigned type, pgoff_t offset)
{
if (frontswap_enabled)
if (frontswap_enabled())
__frontswap_invalidate_page(type, offset);
}
static inline void frontswap_invalidate_area(unsigned type)
{
if (frontswap_enabled)
if (frontswap_enabled())
__frontswap_invalidate_area(type);
}
static inline void frontswap_init(unsigned type, unsigned long *map)
{
if (frontswap_enabled)
if (frontswap_enabled())
__frontswap_init(type, map);
}
......
......@@ -20,6 +20,8 @@
#include <linux/frontswap.h>
#include <linux/swapfile.h>
DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key);
/*
* frontswap_ops are added by frontswap_register_ops, and provide the
* frontswap "backend" implementation functions. Multiple implementations
......@@ -139,6 +141,8 @@ void frontswap_register_ops(struct frontswap_ops *ops)
ops->next = frontswap_ops;
} while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next);
static_branch_inc(&frontswap_enabled_key);
spin_lock(&swap_lock);
plist_for_each_entry(si, &swap_active_head, list) {
if (si->frontswap_map)
......@@ -189,7 +193,7 @@ void __frontswap_init(unsigned type, unsigned long *map)
struct swap_info_struct *sis = swap_info[type];
struct frontswap_ops *ops;
BUG_ON(sis == NULL);
VM_BUG_ON(sis == NULL);
/*
* p->frontswap is a bitmap that we MUST have to figure out which page
......@@ -248,15 +252,9 @@ int __frontswap_store(struct page *page)
pgoff_t offset = swp_offset(entry);
struct frontswap_ops *ops;
/*
* Return if no backend registed.
* Don't need to inc frontswap_failed_stores here.
*/
if (!frontswap_ops)
return -1;
BUG_ON(!PageLocked(page));
BUG_ON(sis == NULL);
VM_BUG_ON(!frontswap_ops);
VM_BUG_ON(!PageLocked(page));
VM_BUG_ON(sis == NULL);
/*
* If a dup, we must remove the old page first; we can't leave the
......@@ -303,11 +301,10 @@ int __frontswap_load(struct page *page)
pgoff_t offset = swp_offset(entry);
struct frontswap_ops *ops;
if (!frontswap_ops)
return -1;
VM_BUG_ON(!frontswap_ops);
VM_BUG_ON(!PageLocked(page));
VM_BUG_ON(sis == NULL);
BUG_ON(!PageLocked(page));
BUG_ON(sis == NULL);
if (!__frontswap_test(sis, offset))
return -1;
......@@ -337,10 +334,9 @@ void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
struct swap_info_struct *sis = swap_info[type];
struct frontswap_ops *ops;
if (!frontswap_ops)
return;
VM_BUG_ON(!frontswap_ops);
VM_BUG_ON(sis == NULL);
BUG_ON(sis == NULL);
if (!__frontswap_test(sis, offset))
return;
......@@ -360,10 +356,9 @@ void __frontswap_invalidate_area(unsigned type)
struct swap_info_struct *sis = swap_info[type];
struct frontswap_ops *ops;
if (!frontswap_ops)
return;
VM_BUG_ON(!frontswap_ops);
VM_BUG_ON(sis == NULL);
BUG_ON(sis == NULL);
if (sis->frontswap_map == NULL)
return;
......
......@@ -2493,7 +2493,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
goto bad_swap;
}
/* frontswap enabled? set up bit-per-page map for frontswap */
if (frontswap_enabled)
if (IS_ENABLED(CONFIG_FRONTSWAP))
frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long));
if (p->bdev &&(swap_flags & SWAP_FLAG_DISCARD) && swap_discardable(p)) {
......
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