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

[Zi Yan]

On Sat Aug 1, 2026 at 10:32 AM EDT, Usama Arif wrote:
> On Fri, 31 Jul 2026 22:13:25 -0400 Zi Yan <ziy@xxxxxxxxxx> wrote:
>
>> 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.
>> 
>
> nit: only "in the" ring buffer?

Will fix it.
>
>> 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;
>> -
>
>
> For order 0, 1 << 0 is 1, which is exactly what the !PagePrivate(page) so LGTM.
>
> The commit message probably needs more text but everything else looks good.
>
> Feel free to add
>
> Acked-by: Usama Arif <usama.arif@xxxxxxxxx>

Thanks. Will add order 0 explanation to the commit message.
>
>
>>  	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
>> 
>> 




-- 
Best Regards,
Yan, Zi