linux-kernel - Re: [RFC PATCH V2 12/13] trace/kscand: Add tracing of scanning and migration

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Message-Id: <20250624160958.e36196456a4c8befc99717ba@kernel.org>
Date: Tue, 24 Jun 2025 16:09:58 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Raghavendra K T <raghavendra.kt@....com>
Cc: <AneeshKumar.KizhakeVeetil@....com>, <Hasan.Maruf@....com>,
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Subject: Re: [RFC PATCH V2 12/13] trace/kscand: Add tracing of scanning and
 migration

On Tue, 24 Jun 2025 05:56:16 +0000
Raghavendra K T <raghavendra.kt@....com> wrote:

> Add tracing support to track
>  - start and end of scanning.
>  - migration.
> 
> CC: Steven Rostedt <rostedt@...dmis.org>
> CC: Masami Hiramatsu <mhiramat@...nel.org>
> CC: linux-trace-kernel@...r.kernel.org
> 
> Signed-off-by: Raghavendra K T <raghavendra.kt@....com>
> ---
>  include/trace/events/kmem.h | 90 +++++++++++++++++++++++++++++++++++++
>  mm/kscand.c                 |  8 ++++
>  2 files changed, 98 insertions(+)
> 
> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> index f74925a6cf69..682c4015414f 100644
> --- a/include/trace/events/kmem.h
> +++ b/include/trace/events/kmem.h
> @@ -9,6 +9,96 @@
>  #include <linux/tracepoint.h>
>  #include <trace/events/mmflags.h>
>  

Please make sure the event is not exposed when it is not used.

#ifdef CONFIG_KSCAND

Thank you,

> +DECLARE_EVENT_CLASS(kmem_mm_class,
> +
> +	TP_PROTO(struct mm_struct *mm),
> +
> +	TP_ARGS(mm),
> +
> +	TP_STRUCT__entry(
> +		__field(	struct mm_struct *, mm		)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->mm = mm;
> +	),
> +
> +	TP_printk("mm = %p", __entry->mm)
> +);
> +
> +DEFINE_EVENT(kmem_mm_class, kmem_mm_enter,
> +	TP_PROTO(struct mm_struct *mm),
> +	TP_ARGS(mm)
> +);
> +
> +DEFINE_EVENT(kmem_mm_class, kmem_mm_exit,
> +	TP_PROTO(struct mm_struct *mm),
> +	TP_ARGS(mm)
> +);
> +
> +DEFINE_EVENT(kmem_mm_class, kmem_scan_mm_start,
> +	TP_PROTO(struct mm_struct *mm),
> +	TP_ARGS(mm)
> +);
> +
> +TRACE_EVENT(kmem_scan_mm_end,
> +
> +	TP_PROTO( struct mm_struct *mm,
> +		 unsigned long start,
> +		 unsigned long total,
> +		 unsigned long scan_period,
> +		 unsigned long scan_size,
> +		 int target_node),
> +
> +	TP_ARGS(mm, start, total, scan_period, scan_size, target_node),
> +
> +	TP_STRUCT__entry(
> +		__field(	struct mm_struct *, mm		)
> +		__field(	unsigned long,   start		)
> +		__field(	unsigned long,   total		)
> +		__field(	unsigned long,   scan_period	)
> +		__field(	unsigned long,   scan_size	)
> +		__field(	int,		 target_node	)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->mm = mm;
> +		__entry->start = start;
> +		__entry->total = total;
> +		__entry->scan_period  = scan_period;
> +		__entry->scan_size    = scan_size;
> +		__entry->target_node  = target_node;
> +	),
> +
> +	TP_printk("mm=%p, start = %ld, total = %ld, scan_period = %ld, scan_size = %ld node = %d",
> +		__entry->mm, __entry->start, __entry->total, __entry->scan_period,
> +		__entry->scan_size, __entry->target_node)
> +);
> +
> +TRACE_EVENT(kmem_scan_mm_migrate,
> +
> +	TP_PROTO(struct mm_struct *mm,
> +		 int rc,
> +		 int target_node),
> +
> +	TP_ARGS(mm, rc, target_node),
> +
> +	TP_STRUCT__entry(
> +		__field(	struct mm_struct *, mm		)
> +		__field(	int,   rc			)
> +		__field(	int,   target_node		)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->mm = mm;
> +		__entry->rc = rc;
> +		__entry->target_node = target_node;
> +	),
> +
> +	TP_printk("mm = %p rc = %d node = %d",
> +		__entry->mm, __entry->rc, __entry->target_node)
> +);
> +
>  TRACE_EVENT(kmem_cache_alloc,
>  
>  	TP_PROTO(unsigned long call_site,
> diff --git a/mm/kscand.c b/mm/kscand.c
> index db7b2f940f36..029d6d2bedc3 100644
> --- a/mm/kscand.c
> +++ b/mm/kscand.c
> @@ -1035,6 +1035,7 @@ static void kmigrated_migrate_mm(struct kmigrated_mm_slot *mm_slot)
>  			}
>  
>  			ret = kmigrated_promote_folio(info, mm, dest);
> +			trace_kmem_scan_mm_migrate(mm, ret, dest);
>  
>  			/* TBD: encode migrated count here, currently assume folio_nr_pages */
>  			if (!ret)
> @@ -1230,6 +1231,9 @@ static unsigned long kscand_scan_mm_slot(void)
>  	mm_target_node = READ_ONCE(mm->target_node);
>  	if (mm_target_node != mm_slot_target_node)
>  		WRITE_ONCE(mm->target_node, mm_slot_target_node);
> +
> +	trace_kmem_scan_mm_start(mm);
> +
>  	now = jiffies;
>  
>  	if (mm_slot_next_scan && time_before(now, mm_slot_next_scan))
> @@ -1300,6 +1304,8 @@ static unsigned long kscand_scan_mm_slot(void)
>  		kscand_update_mmslot_info(mm_slot, total, target_node);
>  	}
>  
> +	trace_kmem_scan_mm_end(mm, address, total, mm_slot_scan_period,
> +			mm_slot_scan_size, target_node);
>  
>  outerloop:
>  	/* exit_mmap will destroy ptes after this */
> @@ -1453,6 +1459,7 @@ void __kscand_enter(struct mm_struct *mm)
>  	spin_unlock(&kscand_mm_lock);
>  
>  	mmgrab(mm);
> +	trace_kmem_mm_enter(mm);
>  	if (wakeup)
>  		wake_up_interruptible(&kscand_wait);
>  }
> @@ -1463,6 +1470,7 @@ void __kscand_exit(struct mm_struct *mm)
>  	struct mm_slot *slot;
>  	int free = 0, serialize = 1;
>  
> +	trace_kmem_mm_exit(mm);
>  	spin_lock(&kscand_mm_lock);
>  	slot = mm_slot_lookup(kscand_slots_hash, mm);
>  	mm_slot = mm_slot_entry(slot, struct kscand_mm_slot, slot);
> -- 
> 2.34.1
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>