Re: [PATCH] mm/page_alloc: add tracepoint for PCP refills

[Vishal Moola <vishal.moola@gmail.com>]

On Sat, Apr 25, 2026 at 05:13:35PM +0800, Bunyod Suvonov wrote:
> The page allocator already has mm_page_pcpu_drain to trace pages
> drained from the per-cpu page lists back to the buddy allocator. There
> is no matching tracepoint for the opposite direction, where
> rmqueue_bulk() refills a PCP list from the buddy allocator.

This sounds like a reasonable idea. Does this tracepoint show us
something that a workload might care about? Not opposed, just curious.

For future versions, would you mind including documentation about it
in Documentation/trace/events-kmem.rst?

> mm_page_alloc_zone_locked is not a good substitute for this. It is
> emitted from __rmqueue_smallest(), which is used both by rmqueue_bulk()
> and by the direct buddy allocation path. Its percpu_refill field is
> derived from the allocation order and migratetype, so it does not
> reliably identify whether the allocation came from a PCP refill.
> 
> Add mm_page_pcpu_refill and emit it from rmqueue_bulk() for each page
> added to the PCP list. The new tracepoint uses the same page, order and
> migratetype fields as mm_page_pcpu_drain, making refill and drain
> activity directly comparable.
> 
> Signed-off-by: Bunyod Suvonov <b.suvonov@sjtu.edu.cn>
> ---
>  include/trace/events/kmem.h | 23 +++++++++++++++++++++++
>  mm/page_alloc.c             |  1 +
>  2 files changed, 24 insertions(+)
> 
> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> index cd7920c81f85..16985604fc51 100644
> --- a/include/trace/events/kmem.h
> +++ b/include/trace/events/kmem.h
> @@ -243,6 +243,29 @@ DEFINE_EVENT(mm_page, mm_page_alloc_zone_locked,
>  	TP_ARGS(page, order, migratetype, percpu_refill)
>  );
>  
> +TRACE_EVENT(mm_page_pcpu_refill,
> +
> +	TP_PROTO(struct page *page, unsigned int order, int migratetype),
> +
> +	TP_ARGS(page, order, migratetype),
> +
> +	TP_STRUCT__entry(
> +		__field(	unsigned long,	pfn		)
> +		__field(	unsigned int,	order		)
> +		__field(	int,		migratetype	)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->pfn		= page ? page_to_pfn(page) : -1UL;
> +		__entry->order		= order;
> +		__entry->migratetype	= migratetype;
> +	),
> +
> +	TP_printk("page=%p pfn=0x%lx order=%d migratetype=%d",
> +		pfn_to_page(__entry->pfn), __entry->pfn,
> +		__entry->order, __entry->migratetype)
> +);
> +
>  TRACE_EVENT(mm_page_pcpu_drain,
>  
>  	TP_PROTO(struct page *page, unsigned int order, int migratetype),
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 65e205111553..a60b73ed39a4 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2544,6 +2544,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
>  		 * pages are ordered properly.
>  		 */
>  		list_add_tail(&page->pcp_list, list);
> +		trace_mm_page_pcpu_refill(page, order, migratetype);

If you're trying to trace all pages as they come onto the pcp lists,
should you also account for the free_frozen_page_commit() path?

>  	}
>  	spin_unlock_irqrestore(&zone->lock, flags);
>  
> -- 
> 2.53.0
>