[PATCH v2 7/7] mm, page_alloc: add static key for should_fail_alloc_page()

[Vlastimil Babka <vbabka@suse.cz>]

Similarly to should_failslab(), remove the overhead of calling the
noinline function should_fail_alloc_page() with a static key that guards
the callsite in the page allocator hotpath, and is controlled by the
fault and error injection frameworks and bpf.

Additionally, compile out all relevant code if neither
CONFIG_FAIL_ALLOC_PAGE nor CONFIG_FUNCTION_ERROR_INJECTION is enabled.
When only the latter is not enabled, make should_fail_alloc_page()
static inline instead of noinline.

No measurement was done other than verifying the should_fail_alloc_page
is gone from the perf profile. A measurement with the analogical change
for should_failslab() suggests that for a page allocator intensive
workload there might be noticeable improvement. It also makes
CONFIG_FAIL_ALLOC_PAGE an option suitable not only for debug kernels.

Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 include/linux/fault-inject.h |  3 ++-
 mm/fail_page_alloc.c         |  3 ++-
 mm/internal.h                |  2 ++
 mm/page_alloc.c              | 30 +++++++++++++++++++++++++++---
 4 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/include/linux/fault-inject.h b/include/linux/fault-inject.h
index 0d0fa94dc1c8..1a782042ae80 100644
--- a/include/linux/fault-inject.h
+++ b/include/linux/fault-inject.h
@@ -96,8 +96,9 @@ static inline void fault_config_init(struct fault_config *config,
 
 struct kmem_cache;
 
+#ifdef CONFIG_FUNCTION_ERROR_INJECTION
 bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order);
-
+#endif
 #ifdef CONFIG_FAIL_PAGE_ALLOC
 bool __should_fail_alloc_page(gfp_t gfp_mask, unsigned int order);
 #else
diff --git a/mm/fail_page_alloc.c b/mm/fail_page_alloc.c
index b1b09cce9394..0906b76d78e8 100644
--- a/mm/fail_page_alloc.c
+++ b/mm/fail_page_alloc.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/fault-inject.h>
 #include <linux/mm.h>
+#include "internal.h"
 
 static struct {
 	struct fault_attr attr;
@@ -9,7 +10,7 @@ static struct {
 	bool ignore_gfp_reclaim;
 	u32 min_order;
 } fail_page_alloc = {
-	.attr = FAULT_ATTR_INITIALIZER,
+	.attr = FAULT_ATTR_INITIALIZER_KEY(&should_fail_alloc_page_active.key),
 	.ignore_gfp_reclaim = true,
 	.ignore_gfp_highmem = true,
 	.min_order = 1,
diff --git a/mm/internal.h b/mm/internal.h
index b2c75b12014e..8539e39b02e6 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -410,6 +410,8 @@ extern char * const zone_names[MAX_NR_ZONES];
 /* perform sanity checks on struct pages being allocated or freed */
 DECLARE_STATIC_KEY_MAYBE(CONFIG_DEBUG_VM, check_pages_enabled);
 
+DECLARE_STATIC_KEY_FALSE(should_fail_alloc_page_active);
+
 extern int min_free_kbytes;
 
 void setup_per_zone_wmarks(void);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2e22ce5675ca..b6e246acb4aa 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3008,11 +3008,35 @@ struct page *rmqueue(struct zone *preferred_zone,
 	return page;
 }
 
-noinline bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
+#if defined(CONFIG_FUNCTION_ERROR_INJECTION) || defined(CONFIG_FAIL_PAGE_ALLOC)
+DEFINE_STATIC_KEY_FALSE(should_fail_alloc_page_active);
+
+#ifdef CONFIG_FUNCTION_ERROR_INJECTION
+noinline
+#else
+static inline
+#endif
+bool should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)
 {
 	return __should_fail_alloc_page(gfp_mask, order);
 }
-ALLOW_ERROR_INJECTION(should_fail_alloc_page, TRUE);
+ALLOW_ERROR_INJECTION_KEY(should_fail_alloc_page, TRUE, &should_fail_alloc_page_active);
+
+static __always_inline bool
+should_fail_alloc_page_wrapped(gfp_t gfp_mask, unsigned int order)
+{
+	if (static_branch_unlikely(&should_fail_alloc_page_active))
+		return should_fail_alloc_page(gfp_mask, order);
+
+	return false;
+}
+#else
+static __always_inline bool
+should_fail_alloc_page_wrapped(gfp_t gfp_mask, unsigned int order)
+{
+	return false;
+}
+#endif
 
 static inline long __zone_watermark_unusable_free(struct zone *z,
 				unsigned int order, unsigned int alloc_flags)
@@ -4430,7 +4454,7 @@ static inline bool prepare_alloc_pages(gfp_t gfp_mask, unsigned int order,
 
 	might_alloc(gfp_mask);
 
-	if (should_fail_alloc_page(gfp_mask, order))
+	if (should_fail_alloc_page_wrapped(gfp_mask, order))
 		return false;
 
 	*alloc_flags = gfp_to_alloc_flags_cma(gfp_mask, *alloc_flags);

-- 
2.45.2