Re: [PATCH 2/3] mm/page_alloc: Add trace event for per-zone lowmem reserve setup

[Kalesh Singh <kaleshsingh@google.com>]

On Sun, Mar 2, 2025 at 11:36 PM Martin Liu <liumartin@google.com> wrote:
>
> This commit introduces the `mm_setup_per_zone_lowmem_reserve` trace
> event,which provides detailed insights into the kernel's per-zone lowmem
> reserve configuration.
>
> The trace event provides precise timestamps, allowing developers to
>
> 1. Correlate lowmem reserve changes with specific kernel events and
> able to diagnose unexpected kswapd or direct reclaim behavior
> triggered by dynamic changes in lowmem reserve.
>
> 2. know memory allocation failures that occur due to insufficient lowmem
> reserve, by precisely correlating allocation attempts with reserve
> adjustments.
>
> Signed-off-by: Martin Liu <liumartin@google.com>
> ---
>  include/trace/events/kmem.h | 27 +++++++++++++++++++++++++++
>  mm/page_alloc.c             |  2 ++
>  2 files changed, 29 insertions(+)
>
> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> index 5fd392dae503..9623e68d4d26 100644
> --- a/include/trace/events/kmem.h
> +++ b/include/trace/events/kmem.h
> @@ -375,6 +375,33 @@ TRACE_EVENT(mm_setup_per_zone_wmarks,
>                   __entry->watermark_promo)
>  );
>
> +TRACE_EVENT(mm_setup_per_zone_lowmem_reserve,
> +
> +       TP_PROTO(struct zone *zone, struct zone *upper_zone, long lowmem_reserve),
> +
> +       TP_ARGS(zone, upper_zone, lowmem_reserve),
> +
> +       TP_STRUCT__entry(
> +               __field(int, node_id)
> +               __string(name, zone->name)
> +               __string(upper_name, upper_zone->name)
> +               __field(long, lowmem_reserve)
> +       ),
> +
> +       TP_fast_assign(
> +               __entry->node_id = zone->zone_pgdat->node_id;
> +               __assign_str(name);
> +               __assign_str(upper_name);
> +               __entry->lowmem_reserve = lowmem_reserve;
> +       ),
> +
> +       TP_printk("node_id=%d zone name=%s upper_zone name=%s lowmem_reserve_pages=%ld",
> +                 __entry->node_id,
> +                 __get_str(name),
> +                 __get_str(upper_name),
> +                 __entry->lowmem_reserve)
> +);
> +
>  /*
>   * Required for uniquely and securely identifying mm in rss_stat tracepoint.
>   */
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 50893061db66..48623a2bf1ac 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5857,6 +5857,8 @@ static void setup_per_zone_lowmem_reserve(void)
>                                         zone->lowmem_reserve[j] = 0;
>                                 else
>                                         zone->lowmem_reserve[j] = managed_pages / ratio;
> +                               trace_mm_setup_per_zone_lowmem_reserve(zone, upper_zone,
> +                                                                                                          zone->lowmem_reserve[j]);

Hi Martin,

Please use 8-character width tabs for indentation.

-- Kalesh
>                         }
>                 }
>         }
> --
> 2.48.1.711.g2feabab25a-goog
>
>