[PATCH 1/3] mm, debug_pagelloc: use static keys to enable debugging

From: Vlastimil Babka
Date: Mon Jun 03 2019 - 10:39:12 EST


CONFIG_DEBUG_PAGEALLOC has been redesigned by 031bc5743f15
("mm/debug-pagealloc: make debug-pagealloc boottime configurable") to allow
being always enabled in a distro kernel, but only perform its expensive
functionality when booted with debug_pagelloc=on. We can further reduce
the overhead when not boot-enabled (including page allocator fast paths) using
static keys. This patch introduces one for debug_pagealloc core functionality,
and another for the optional guard page functionality (enabled by booting with
debug_guardpage_minorder=X).

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
include/linux/mm.h | 15 +++++++++++----
mm/page_alloc.c | 23 +++++++++++++++++------
2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0e8834ac32b7..c71ed22769f3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2685,11 +2685,18 @@ static inline void kernel_poison_pages(struct page *page, int numpages,
int enable) { }
#endif

-extern bool _debug_pagealloc_enabled;
+#ifdef CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT
+DECLARE_STATIC_KEY_TRUE(_debug_pagealloc_enabled);
+#else
+DECLARE_STATIC_KEY_FALSE(_debug_pagealloc_enabled);
+#endif

static inline bool debug_pagealloc_enabled(void)
{
- return IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) && _debug_pagealloc_enabled;
+ if (!IS_ENABLED(CONFIG_DEBUG_PAGEALLOC))
+ return false;
+
+ return static_branch_unlikely(&_debug_pagealloc_enabled);
}

#if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP)
@@ -2843,7 +2850,7 @@ extern struct page_ext_operations debug_guardpage_ops;

#ifdef CONFIG_DEBUG_PAGEALLOC
extern unsigned int _debug_guardpage_minorder;
-extern bool _debug_guardpage_enabled;
+DECLARE_STATIC_KEY_FALSE(_debug_guardpage_enabled);

static inline unsigned int debug_guardpage_minorder(void)
{
@@ -2852,7 +2859,7 @@ static inline unsigned int debug_guardpage_minorder(void)

static inline bool debug_guardpage_enabled(void)
{
- return _debug_guardpage_enabled;
+ return static_branch_unlikely(&_debug_guardpage_enabled);
}

static inline bool page_is_guard(struct page *page)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d66bc8abe0af..639f1f9e74c5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -646,16 +646,27 @@ void prep_compound_page(struct page *page, unsigned int order)

#ifdef CONFIG_DEBUG_PAGEALLOC
unsigned int _debug_guardpage_minorder;
-bool _debug_pagealloc_enabled __read_mostly
- = IS_ENABLED(CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT);
+
+#ifdef CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT
+DEFINE_STATIC_KEY_TRUE(_debug_pagealloc_enabled);
+#else
+DEFINE_STATIC_KEY_FALSE(_debug_pagealloc_enabled);
+#endif
EXPORT_SYMBOL(_debug_pagealloc_enabled);
-bool _debug_guardpage_enabled __read_mostly;
+
+DEFINE_STATIC_KEY_FALSE(_debug_guardpage_enabled);

static int __init early_debug_pagealloc(char *buf)
{
- if (!buf)
+ bool enable = false;
+
+ if (kstrtobool(buf, &enable))
return -EINVAL;
- return kstrtobool(buf, &_debug_pagealloc_enabled);
+
+ if (enable)
+ static_branch_enable(&_debug_pagealloc_enabled);
+
+ return 0;
}
early_param("debug_pagealloc", early_debug_pagealloc);

@@ -679,7 +690,7 @@ static void init_debug_guardpage(void)
if (!debug_guardpage_minorder())
return;

- _debug_guardpage_enabled = true;
+ static_branch_enable(&_debug_guardpage_enabled);
}

struct page_ext_operations debug_guardpage_ops = {
--
2.21.0