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

[Usama Arif <usama.arif@linux.dev>]

On Fri, 31 Jul 2026 22:13:25 -0400 Zi Yan <ziy@nvidia.com> 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?

> 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@nvidia.com>
> To: Peter Zijlstra <peterz@infradead.org>
> To: Ingo Molnar <mingo@redhat.com>
> To: Arnaldo Carvalho de Melo <acme@kernel.org>
> To: Namhyung Kim <namhyung@kernel.org>
> To: Thomas Gleixner <tglx@kernel.org>
> To: Borislav Petkov <bp@alien8.de>
> To: Dave Hansen <dave.hansen@linux.intel.com>
> To: x86@kernel.org
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Ian Rogers <irogers@google.com>
> Cc: Adrian Hunter <adrian.hunter@intel.com>
> Cc: James Clark <james.clark@linaro.org>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: linux-perf-users@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> ---
>  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@linux.dev>


>  	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
> 
>