init_on_alloc: Optimize static branches

The state of CONFIG_INIT_ON_ALLOC_DEFAULT_ON (and ...ON_FREE...) did not
change the assembly ordering of the static branches: they were always out
of line. Use the new jump_label macros to check the CONFIG settings to
default to the "expected" state, which slightly optimizes the resulting
assembly code.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexander Potapenko <glider@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Link: https://lore.kernel.org/r/20210401232347.2791257-3-keescook@chromium.org

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8ba4342..616dcaf 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2904,18 +2904,20 @@ static inline void kernel_poison_pages(struct page *page, int numpages) { }
 static inline void kernel_unpoison_pages(struct page *page, int numpages) { }
 #endif
 
-DECLARE_STATIC_KEY_FALSE(init_on_alloc);
+DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc);
 static inline bool want_init_on_alloc(gfp_t flags)
 {
-       if (static_branch_unlikely(&init_on_alloc))
+       if (static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON,
+                               &init_on_alloc))
                return true;
        return flags & __GFP_ZERO;
 }
 
-DECLARE_STATIC_KEY_FALSE(init_on_free);
+DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free);
 static inline bool want_init_on_free(void)
 {
-       return static_branch_unlikely(&init_on_free);
+       return static_branch_maybe(CONFIG_INIT_ON_FREE_DEFAULT_ON,
+                                  &init_on_free);
 }
 
 extern bool _debug_pagealloc_enabled_early;

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cfc7287..e2f19bf 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -167,10 +167,10 @@ unsigned long totalcma_pages __read_mostly;
 
 int percpu_pagelist_fraction;
 gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
-DEFINE_STATIC_KEY_FALSE(init_on_alloc);
+DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc);
 EXPORT_SYMBOL(init_on_alloc);
 
-DEFINE_STATIC_KEY_FALSE(init_on_free);
+DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free);
 EXPORT_SYMBOL(init_on_free);
 
 static bool _init_on_alloc_enabled_early __read_mostly

diff --git a/mm/slab.h b/mm/slab.h
index 076582f..774c722 100644 (file)
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -601,7 +601,8 @@ static inline void cache_random_seq_destroy(struct kmem_cache *cachep) { }
 
 static inline bool slab_want_init_on_alloc(gfp_t flags, struct kmem_cache *c)
 {
-       if (static_branch_unlikely(&init_on_alloc)) {
+       if (static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON,
+                               &init_on_alloc)) {
                if (c->ctor)
                        return false;
                if (c->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON))
@@ -613,7 +614,8 @@ static inline bool slab_want_init_on_alloc(gfp_t flags, struct kmem_cache *c)
 
 static inline bool slab_want_init_on_free(struct kmem_cache *c)
 {
-       if (static_branch_unlikely(&init_on_free))
+       if (static_branch_maybe(CONFIG_INIT_ON_FREE_DEFAULT_ON,
+                               &init_on_free))
                return !(c->ctor ||
                         (c->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)));
        return false;