linux-kernel - Re: [PATCH v2 1/2] hugetlb: memcg: account hugetlb-backed memory in memory controller

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Message-ID: <CAJD7tkanr99d_Y=LefQTFsykyiO5oZpPUC=suD3P-L5eS=0SXA@mail.gmail.com>
Date:   Thu, 28 Sep 2023 17:38:01 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Nhat Pham <nphamcs@...il.com>
Cc:     akpm@...ux-foundation.org, riel@...riel.com, hannes@...xchg.org,
        mhocko@...nel.org, roman.gushchin@...ux.dev, shakeelb@...gle.com,
        muchun.song@...ux.dev, tj@...nel.org, lizefan.x@...edance.com,
        shuah@...nel.org, mike.kravetz@...cle.com, linux-mm@...ck.org,
        kernel-team@...a.com, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org
Subject: Re: [PATCH v2 1/2] hugetlb: memcg: account hugetlb-backed memory in
 memory controller

<snip>

>
> +
> +/**
> + * mem_cgroup_hugetlb_charge_folio - Charge a newly allocated hugetlb folio.
> + * @folio: folio to charge.
> + * @gfp: reclaim mode
> + *
> + * This function charges an allocated hugetlbf folio to the memcg of the
> + * current task.
> + *
> + * Returns 0 on success. Otherwise, an error code is returned.
> + */
> +int mem_cgroup_hugetlb_charge_folio(struct folio *folio, gfp_t gfp)
> +{
> +       struct mem_cgroup *memcg;
> +       int ret;
> +
> +       if (mem_cgroup_disabled() ||
> +               !(cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING))

What happens if the memory controller is mounted in a cgroup v1
hierarchy? It appears to me that we *will* go through with hugetlb
charging in this case?

>
> +               return 0;
> +
> +       memcg = get_mem_cgroup_from_current();
> +       ret = charge_memcg(folio, memcg, gfp);
> +       mem_cgroup_put(memcg);
> +
> +       return ret;
> +}
> +
>  /**
>   * mem_cgroup_swapin_charge_folio - Charge a newly allocated folio for swapin.
>   * @folio: folio to charge.
> --
> 2.34.1