Re: [PATCH v3 1/1] memcg/hugetlb: Adding hugeTLB counters to memcg

[Michal Hocko <mhocko@suse.com>]

On Mon 28-10-24 14:05:05, Joshua Hahn wrote:
[...]
> Changelog
> v3:
>   * Removed check for whether CGRP_ROOT_HUGETLB_ACCOUNTING is on, since
>     this check is already handled by lruvec_stat_mod (and doing the
>     check in hugetlb.c actually breaks the build if MEMCG is not
>     enabled.
[...]
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 190fa05635f4..fbb10e52d7ea 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1925,6 +1925,7 @@ void free_huge_folio(struct folio *folio)
>  				     pages_per_huge_page(h), folio);
>  	hugetlb_cgroup_uncharge_folio_rsvd(hstate_index(h),
>  					  pages_per_huge_page(h), folio);
> +	lruvec_stat_mod_folio(folio, NR_HUGETLB, -pages_per_huge_page(h));
>  	mem_cgroup_uncharge(folio);
>  	if (restore_reserve)
>  		h->resv_huge_pages++;
> @@ -3093,6 +3094,7 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
>  
>  	if (!memcg_charge_ret)
>  		mem_cgroup_commit_charge(folio, memcg);
> +	lruvec_stat_mod_folio(folio, NR_HUGETLB, pages_per_huge_page(h));
>  	mem_cgroup_put(memcg);
>  
>  	return folio;

I do not see any specific checks for CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING
in these paths. I guess you wanted to say that you rely on
mem_cgroup_commit_charge setting memcg pointer which then __lruvec_stat_mod_folio
relies on when updating stats.

I suspect this all is done because you want a global counter to be
updated as well, right? Changelog doesn't say anything about that
though. Why is this needed when /proc/meminfo already describes the
global hugetlb usage?
-- 
Michal Hocko
SUSE Labs