[PATCH RFC 02/14] perf/ring_buffer: stop using PG_private as AUX page high-order marker

[Zi Yan]

A high-order AUX page sets PG_private on its first page and stores the
order in first_page->private. Stop using PG_private and check
first_page->private for AUX page order only ring buffer and its users.

It prepares for a future commit that remove PG_private.

No functional change intended.

Assisted-by: Claude:claude-opus-4-8
Assisted-by: Codex:gpt-5
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
To: Ingo Molnar <mingo@xxxxxxxxxx>
To: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
To: Namhyung Kim <namhyung@xxxxxxxxxx>
To: Thomas Gleixner <tglx@xxxxxxxxxx>
To: Borislav Petkov <bp@xxxxxxxxx>
To: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
To: x86@xxxxxxxxxx
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: James Clark <james.clark@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: linux-perf-users@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 arch/x86/events/intel/bts.c | 3 ---
 arch/x86/events/intel/pt.c  | 6 ++----
 kernel/events/ring_buffer.c | 7 +++----
 3 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index cbac54cb3a9ec..5849392cf26d5 100644
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -66,9 +66,6 @@ static struct pmu bts_pmu;
 
 static int buf_nr_pages(struct page *page)
 {
-	if (!PagePrivate(page))
-		return 1;
-
 	return 1 << page_private(page);
 }
 
diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index b5726b50e77db..29d8b4a3560cd 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -774,8 +774,7 @@ static int topa_insert_pages(struct pt_buffer *buf, int cpu, gfp_t gfp)
 	struct page *p;
 
 	p = virt_to_page(buf->data_pages[buf->nr_pages]);
-	if (PagePrivate(p))
-		order = page_private(p);
+	order = page_private(p);
 
 	if (topa_table_full(topa)) {
 		topa = topa_alloc(cpu, gfp);
@@ -1289,8 +1288,7 @@ static int pt_buffer_try_single(struct pt_buffer *buf, int nr_pages)
 	if (!intel_pt_validate_hw_cap(PT_CAP_single_range_output))
 		goto out;
 
-	if (PagePrivate(p))
-		order = page_private(p);
+	order = page_private(p);
 
 	if (1 << order != nr_pages)
 		goto out;
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 9fe92161715e0..061b5cb222266 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -630,11 +630,10 @@ static struct page *rb_alloc_aux_page(int node, int order)
 		/*
 		 * Communicate the allocation size to the driver:
 		 * if we managed to secure a high-order allocation,
-		 * set its first page's private to this order;
-		 * !PagePrivate(page) means it's just a normal page.
+		 * set its first page's private to this order, otherwise page's
+		 * private remains zero.
 		 */
 		split_page(page, order);
-		SetPagePrivate(page);
 		set_page_private(page, order);
 	}
 
@@ -645,7 +644,7 @@ static void rb_free_aux_page(struct perf_buffer *rb, int idx)
 {
 	struct page *page = virt_to_page(rb->aux_pages[idx]);
 
-	ClearPagePrivate(page);
+	set_page_private(page, 0);
 	__free_page(page);
 }
 

-- 
2.53.0