Re: [PATCH v2 1/2] mm: vmscan: add cgroup IDs to vmscan tracepoints

[Shakeel Butt <shakeel.butt@linux.dev>]

On Tue, Dec 16, 2025 at 06:02:51AM -0800, Thomas Ballasi wrote:
> Memory reclaim events are currently difficult to attribute to
> specific cgroups, making debugging memory pressure issues
> challenging.  This patch adds memory cgroup ID (memcg_id) to key
> vmscan tracepoints to enable better correlation and analysis.
> 
> For operations not associated with a specific cgroup, the field
> is defaulted to 0.
> 
> Signed-off-by: Thomas Ballasi <tballasi@linux.microsoft.com>
> ---
...
> +		__entry->memcg_id = sc->memcg ? mem_cgroup_id(sc->memcg) : 0;
...
> +		__entry->memcg_id = sc->memcg ? mem_cgroup_id(sc->memcg) : 0;
...
>  
...
>  	trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
> -						      sc.gfp_mask);
> +						      sc.gfp_mask,
> +						      mem_cgroup_id(memcg));
>  

...

> +	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed, mem_cgroup_id(memcg));
...
> +	trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask, mem_cgroup_id(memcg));
...
> +	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed, mem_cgroup_id(memcg));

Please don't use mem_cgroup_id() here as it is an ID internal to memcg.
Use cgroup_id(memcg->css.cgroup) instead which is inode number and is
exposed to the userspace.