Re: [PATCH v6 3/3] mm: vmscan: add PIDs to vmscan tracepoints

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

On Fri, 13 Feb 2026 10:15:37 -0800 Thomas Ballasi <tballasi@linux.microsoft.com> wrote:

> The changes aims at adding additionnal tracepoints variables to help
> debuggers attribute them to specific processes.
> 
> The PID field uses in_task() to reliably detect when we're in process
> context and can safely access current->pid.  When not in process
> context (such as in interrupt or in an asynchronous RCU context), the
> field is set to -1 as a sentinel value.
> 
> Signed-off-by: Thomas Ballasi <tballasi@linux.microsoft.com>
> ---
>  include/trace/events/vmscan.h | 35 +++++++++++++++++++++++++----------
>  1 file changed, 25 insertions(+), 10 deletions(-)
> 
> diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> index 1212f6a7c223e..a68b712ef757a 100644
> --- a/include/trace/events/vmscan.h
> +++ b/include/trace/events/vmscan.h
> @@ -122,18 +122,22 @@ DECLARE_EVENT_CLASS(mm_vmscan_direct_reclaim_begin_template,
>  		__field(	unsigned long,	gfp_flags	)
>  		__field(	u64,	memcg_id	)
>  		__field(	int,	order		)
> +		__field(	int,	pid		)
>  	),
>  
>  	TP_fast_assign(
>  		__entry->gfp_flags	= (__force unsigned long)gfp_flags;
>  		__entry->order		= order;
> +		__entry->pid		= current->pid;
>  		__entry->memcg_id	= mem_cgroup_id(memcg);
>  	),
>  
> -	TP_printk("order=%d gfp_flags=%s memcg_id=%llu",
> +	TP_printk("order=%d gfp_flags=%s pid=%d memcg_id=%llu %s",
>  		__entry->order,
>  		show_gfp_flags(__entry->gfp_flags),
> -		__entry->memcg_id)
> +		__entry->pid,
> +		__entry->memcg_id,
> +		__event_in_irq() ? "(in-irq)" : "")
>  );
>  
>  DEFINE_EVENT(mm_vmscan_direct_reclaim_begin_template, mm_vmscan_direct_reclaim_begin,
> @@ -168,16 +172,20 @@ DECLARE_EVENT_CLASS(mm_vmscan_direct_reclaim_end_template,
>  	TP_STRUCT__entry(
>  		__field(	unsigned long,	nr_reclaimed	)
>  		__field(	u64,	memcg_id	)
> +		__field(	int,	pid		)
>  	),
>  
>  	TP_fast_assign(
>  		__entry->nr_reclaimed	= nr_reclaimed;
>  		__entry->memcg_id	= mem_cgroup_id(memcg);
> +		__entry->pid		= current->pid;
>  	),
>  
> -	TP_printk("nr_reclaimed=%lu memcg_id=%llu",
> +	TP_printk("nr_reclaimed=%lu pid=%d memcg_id=%llu %s",
>  		__entry->nr_reclaimed,
> -		__entry->memcg_id)
> +		__entry->pid,
> +		__entry->memcg_id,
> +		__event_in_irq() ? "(in-irq)" : "")
>  );
>  
>  DEFINE_EVENT(mm_vmscan_direct_reclaim_end_template, mm_vmscan_direct_reclaim_end,
> @@ -220,9 +228,10 @@ TRACE_EVENT(mm_shrink_slab_start,
>  		__field(unsigned long, cache_items)
>  		__field(unsigned long long, delta)
>  		__field(unsigned long, total_scan)
> +		__field(u64, memcg_id)
>  		__field(int, priority)
>  		__field(int, nid)
> -		__field(u64, memcg_id)
> +		__field(int, pid)
>  	),
>  
>  	TP_fast_assign(
> @@ -236,19 +245,22 @@ TRACE_EVENT(mm_shrink_slab_start,
>  		__entry->priority = priority;
>  		__entry->nid = sc->nid;
>  		__entry->memcg_id = mem_cgroup_id(memcg);
> +		__entry->pid = current->pid;
>  	),
>  
> -	TP_printk("%pS %p: nid: %d memcg_id: %llu objects to shrink %ld gfp_flags %s cache items %ld delta %lld total_scan %ld priority %d",
> +	TP_printk("%pS %p: nid: %d pid: %d memcg_id: %llu objects to shrink %ld gfp_flags %s cache items %ld delta %lld total_scan %ld priority %d %s",
>  		__entry->shrink,
>  		__entry->shr,
>  		__entry->nid,
> +		__entry->pid,
>  		__entry->memcg_id,
>  		__entry->nr_objects_to_shrink,
>  		show_gfp_flags(__entry->gfp_flags),
>  		__entry->cache_items,
>  		__entry->delta,
>  		__entry->total_scan,
> -		__entry->priority)
> +		__entry->priority,
> +		__event_in_irq() ? "(in-irq)" : "")
>  );
>  
>  TRACE_EVENT(mm_shrink_slab_end,
> @@ -266,29 +278,32 @@ TRACE_EVENT(mm_shrink_slab_end,
>  		__field(long, total_scan)
>  		__field(int, nid)
>  		__field(int, retval)
> +		__field(int, pid)
>  		__field(u64, memcg_id)
>  	),
>  
>  	TP_fast_assign(
>  		__entry->shr = shr;
> -		__entry->shrink = shr->scan_objects;

__entry->shrink is removed here, but still printed below. Was this an intended
change of this commit?

>  		__entry->unused_scan = unused_scan_cnt;
>  		__entry->new_scan = new_scan_cnt;
>  		__entry->total_scan = total_scan;
>  		__entry->nid = nid;
>  		__entry->retval = shrinker_retval;
> +		__entry->pid = current->pid;
>  		__entry->memcg_id = mem_cgroup_id(memcg);
>  	),
>  
> -	TP_printk("%pS %p: nid: %d memcg_id: %llu unused scan count %ld new scan count %ld total_scan %ld last shrinker return val %d",
> +	TP_printk("%pS %p: nid: %d pid: %d memcg_id: %llu unused scan count %ld new scan count %ld total_scan %ld last shrinker return val %d %s",
>  		__entry->shrink,
>  		__entry->shr,
>  		__entry->nid,
> +		__entry->pid,
>  		__entry->memcg_id,
>  		__entry->unused_scan,
>  		__entry->new_scan,
>  		__entry->total_scan,
> -		__entry->retval)
> +		__entry->retval,
> +		__event_in_irq() ? "(in-irq)" : "")
>  );
>  
>  TRACE_EVENT(mm_vmscan_lru_isolate,
> -- 
> 2.33.8
> 
>