Re: [PATCH v4 3/5] cgroup: change rstat function signatures from cgroup-based to css-based

[Yosry Ahmed <yosry.ahmed@linux.dev>]

On Thu, Apr 03, 2025 at 06:10:48PM -0700, JP Kobryn wrote:
> This non-functional change serves as preparation for moving to
> subsystem-based rstat trees. To simplify future commits, change the
> signatures of existing cgroup-based rstat functions to become css-based and
> rename them to reflect that.
> 
> Though the signatures have changed, the implementations have not. Within
> these functions use the css->cgroup pointer to obtain the associated cgroup
> and allow code to function the same just as it did before this patch. At
> applicable call sites, pass the subsystem-specific css pointer as an
> argument or pass a pointer to cgroup::self if not in subsystem context.
> 
> Note that cgroup_rstat_updated_list() and cgroup_rstat_push_children()
> are not altered yet since there would be a larger amount of css to
> cgroup conversions which may overcomplicate the code at this
> intermediate phase.
> 
> Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
> ---
>  block/blk-cgroup.c                            |  6 +-
>  include/linux/cgroup-defs.h                   |  2 +-
>  include/linux/cgroup.h                        |  4 +-
>  kernel/cgroup/cgroup-internal.h               |  4 +-
>  kernel/cgroup/cgroup.c                        | 30 ++++---
>  kernel/cgroup/rstat.c                         | 83 +++++++++++--------
>  mm/memcontrol.c                               |  4 +-
>  .../bpf/progs/cgroup_hierarchical_stats.c     |  9 +-
>  8 files changed, 80 insertions(+), 62 deletions(-)
> 
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 5905f277057b..0560ea402856 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -1144,7 +1144,7 @@ static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu)
>  /*
>   * We source root cgroup stats from the system-wide stats to avoid
>   * tracking the same information twice and incurring overhead when no
> - * cgroups are defined. For that reason, cgroup_rstat_flush in
> + * cgroups are defined. For that reason, css_rstat_flush in
>   * blkcg_print_stat does not actually fill out the iostat in the root
>   * cgroup's blkcg_gq.
>   *
> @@ -1253,7 +1253,7 @@ static int blkcg_print_stat(struct seq_file *sf, void *v)
>  	if (!seq_css(sf)->parent)
>  		blkcg_fill_root_iostats();
>  	else
> -		cgroup_rstat_flush(blkcg->css.cgroup);
> +		css_rstat_flush(&blkcg->css);
>  
>  	rcu_read_lock();
>  	hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
> @@ -2243,7 +2243,7 @@ void blk_cgroup_bio_start(struct bio *bio)
>  	}
>  
>  	u64_stats_update_end_irqrestore(&bis->sync, flags);
> -	cgroup_rstat_updated(blkcg->css.cgroup, cpu);
> +	css_rstat_updated(&blkcg->css, cpu);
>  	put_cpu();
>  }
>  
> diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
> index 6d177f770d28..e4a9fb00b228 100644
> --- a/include/linux/cgroup-defs.h
> +++ b/include/linux/cgroup-defs.h
> @@ -536,7 +536,7 @@ struct cgroup {
>  	/*
>  	 * A singly-linked list of cgroup structures to be rstat flushed.
>  	 * This is a scratch field to be used exclusively by
> -	 * cgroup_rstat_flush_locked() and protected by cgroup_rstat_lock.
> +	 * css_rstat_flush_locked() and protected by cgroup_rstat_lock.

Also, I believe this function does not exist anymore.