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authorVlastimil Babka <vbabka@suse.cz>2016-07-26 15:24:42 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-07-26 16:19:19 -0700
commit8ea1d2a1985a7ae096edf5850a31d844ad1b8e97 (patch)
tree3ec2c4dc7d51fa1f5f2797e09fd8361a8404b474 /include/linux
parentfbe84a09da746f781553051bb3dbc63f7b0a5162 (diff)
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 CONFIG_FRONTSWAP, which was effectively always true when reachable. The patch just removes this check. Using frontswap_enabled() does not sound correct here, as this can be true even without xen's own backend being registered. - in SYSCALL_DEFINE2(swapon), change the check to IS_ENABLED(CONFIG_FRONTSWAP) as it seems the bitmap allocation cannot currently be postponed until a backend is registered. This means that frontswap will still have some memory overhead by being configured, but without a backend. After the patch, we can expect that some functions in frontswap.c are called only when frontswap_ops is non-NULL. Change the checks there to VM_BUG_ONs. While at it, convert other BUG_ONs to VM_BUG_ONs as frontswap has been stable for some time. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/1463152235-9717-1-git-send-email-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/frontswap.h34
1 files changed, 20 insertions, 14 deletions
diff --git a/include/linux/frontswap.h b/include/linux/frontswap.h
index e65ef959546c..c46d2aa16d81 100644
--- a/include/linux/frontswap.h
+++ b/include/linux/frontswap.h
@@ -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);
}