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

[Martin Liu <liumartin@google.com>]

On Mon, Mar 03, 2025 at 12:18:46AM -0800, Kalesh Singh wrote:
> 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.

Hi Kalesh,

Yes, thank you for the reminders. I will address these once receiving
feedback :)

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