[PATCH 3/3] alloc_tag: uninline code gated by mem_alloc_profiling_key in page allocator

Suren Baghdasaryan
2025-01-26T07:02:14Z

When a sizable code section is protected by a disabled static key, that
code gets into the instruction cache even though it's not executed and
consumes the cache, increasing cache misses. This can be remedied by
moving such code into a separate uninlined function. The improvement
however comes at the expense of the configuration when this static key
gets enabled since there is now an additional function call.
The default state of the mem_alloc_profiling_key is controlled by
CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT. Apply this optimization
only if CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=n, improving the
performance of the default configuration.
When CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=y the functions
are inlined and performance does not change.

On a Pixel6 phone, page allocation profiling overhead measured with
CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=n and profiling disabled:

baseline modified
Big 4.93% 1.53%
Medium 4.39% 1.41%
Little 1.02% 0.36%

When CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=n and memory allocation
profiling gets enabled, the difference in performance before and after
this change stays within noise levels.

On x86 this patch does not make noticeable difference because the overhead
with mem_alloc_profiling_key disabled is much lower (under 1%) to start
with, so any improvement is less visible and hard to distinguish from the
noise.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
include/linux/pgalloc_tag.h | 60 +++-------------------------
mm/page_alloc.c | 78 +++++++++++++++++++++++++++++++++++++
2 files changed, 83 insertions(+), 55 deletions(-)

diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
index 4a82b6b4820e..c74077977830 100644
--- a/include/linux/pgalloc_tag.h
+++ b/include/linux/pgalloc_tag.h
@@ -162,47 +162,13 @@ static inline void update_page_tag_ref(union pgtag_ref_handle handle, union code
}
}

-static inline void clear_page_tag_ref(struct page *page)
-{
- if (mem_alloc_profiling_enabled()) {
- union pgtag_ref_handle handle;
- union codetag_ref ref;
-
- if (get_page_tag_ref(page, &ref, &handle)) {
- set_codetag_empty(&ref);
- update_page_tag_ref(handle, &ref);
- put_page_tag_ref(handle);
- }
- }
-}
-
-static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
- unsigned int nr)
-{
- if (mem_alloc_profiling_enabled()) {
- union pgtag_ref_handle handle;
- union codetag_ref ref;
-
- if (get_page_tag_ref(page, &ref, &handle)) {
- alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr);
- update_page_tag_ref(handle, &ref);
- put_page_tag_ref(handle);
- }
- }
-}
+/* Should be called only if mem_alloc_profiling_enabled() */
+void __clear_page_tag_ref(struct page *page);

-static inline void pgalloc_tag_sub(struct page *page, unsigned int nr)
+static inline void clear_page_tag_ref(struct page *page)
{
- if (mem_alloc_profiling_enabled()) {
- union pgtag_ref_handle handle;
- union codetag_ref ref;
-
- if (get_page_tag_ref(page, &ref, &handle)) {
- alloc_tag_sub(&ref, PAGE_SIZE * nr);
- update_page_tag_ref(handle, &ref);
- put_page_tag_ref(handle);
- }
- }
+ if (mem_alloc_profiling_enabled())
+ __clear_page_tag_ref(page);
}

/* Should be called only if mem_alloc_profiling_enabled() */
@@ -222,18 +188,6 @@ static inline struct alloc_tag *__pgalloc_tag_get(struct page *page)
return tag;
}

-static inline void pgalloc_tag_sub_pages(struct page *page, unsigned int nr)
-{
- struct alloc_tag *tag;
-
- if (!mem_alloc_profiling_enabled())
- return;
-
- tag = __pgalloc_tag_get(page);
- if (tag)
- this_cpu_sub(tag->counters->bytes, PAGE_SIZE * nr);
-}
-
void pgalloc_tag_split(struct folio *folio, int old_order, int new_order);
void pgalloc_tag_swap(struct folio *new, struct folio *old);

@@ -242,10 +196,6 @@ void __init alloc_tag_sec_init(void);
#else /* CONFIG_MEM_ALLOC_PROFILING */

static inline void clear_page_tag_ref(struct page *page) {}
-static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
- unsigned int nr) {}
-static inline void pgalloc_tag_sub(struct page *page, unsigned int nr) {}
-static inline void pgalloc_tag_sub_pages(struct page *page, unsigned int nr) {}
static inline void alloc_tag_sec_init(void) {}
static inline void pgalloc_tag_split(struct folio *folio, int old_order, int new_order) {}
static inline void pgalloc_tag_swap(struct folio *new, struct folio *old) {}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 55ed2f245f80..67e205286dbf 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1041,6 +1041,84 @@ static void kernel_init_pages(struct page *page, int numpages)
kasan_enable_current();
}

+#ifdef CONFIG_MEM_ALLOC_PROFILING
+
+/* Should be called only if mem_alloc_profiling_enabled() */
+void __clear_page_tag_ref(struct page *page)
+{
+ union pgtag_ref_handle handle;
+ union codetag_ref ref;
+
+ if (get_page_tag_ref(page, &ref, &handle)) {
+ set_codetag_empty(&ref);
+ update_page_tag_ref(handle, &ref);
+ put_page_tag_ref(handle);
+ }
+}
+
+/* Should be called only if mem_alloc_profiling_enabled() */
+static inline_if_mem_alloc_prof
+void __pgalloc_tag_add(struct page *page, struct task_struct *task,
+ unsigned int nr)
+{
+ union pgtag_ref_handle handle;
+ union codetag_ref ref;
+
+ if (get_page_tag_ref(page, &ref, &handle)) {
+ alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr);
+ update_page_tag_ref(handle, &ref);
+ put_page_tag_ref(handle);
+ }
+}
+
+static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
+ unsigned int nr)
+{
+ if (mem_alloc_profiling_enabled())
+ __pgalloc_tag_add(page, task, nr);
+}
+
+/* Should be called only if mem_alloc_profiling_enabled() */
+static inline_if_mem_alloc_prof
+void __pgalloc_tag_sub(struct page *page, unsigned int nr)
+{
+ union pgtag_ref_handle handle;
+ union codetag_ref ref;
+
+ if (get_page_tag_ref(page, &ref, &handle)) {
+ alloc_tag_sub(&ref, PAGE_SIZE * nr);
+ update_page_tag_ref(handle, &ref);
+ put_page_tag_ref(handle);
+ }
+}
+
+static inline void pgalloc_tag_sub(struct page *page, unsigned int nr)
+{
+ if (mem_alloc_profiling_enabled())
+ __pgalloc_tag_sub(page, nr);
+}
+
+static inline void pgalloc_tag_sub_pages(struct page *page, unsigned int nr)
+{
+ struct alloc_tag *tag;
+
+ if (!mem_alloc_profiling_enabled())
+ return;
+
+ tag = __pgalloc_tag_get(page);
+ if (tag)
+ this_cpu_sub(tag->counters->bytes, PAGE_SIZE * nr);
+}
+
+#else /* CONFIG_MEM_ALLOC_PROFILING */
+
+static inline void pgalloc_tag_add(struct page *page, struct task_struct *task,
+ unsigned int nr) {}
+static inline void pgalloc_tag_sub(struct page *page, unsigned int nr) {}
+static inline void pgalloc_tag_sub_pages(struct page *page, unsigned int nr) {}
+
+#endif /* CONFIG_MEM_ALLOC_PROFILING */
+
__always_inline bool free_pages_prepare(struct page *page,
unsigned int order)
{
--
2.48.1.262.g85cc9f2d1e-goog