Re: [PATCH v2 1/2] mm/memcontrol: add dmem charge/uncharge functions

[Albert Esteve <aesteve@redhat.com>]

On Tue, May 19, 2026 at 6:01 PM Eric Chanudet <echanude@redhat.com> wrote:
>
> Add mem_cgroup_dmem_charge() and mem_cgroup_dmem_uncharge() to allow
> dmem pool allocations to optionally be double-charged against the memory
> controller. Take the struct cgroup from the dmem pool's css as there is
> no convenient object exported to represent these allocations. These will
> resolve the effective memory css from that cgroup and perform the
> charge.
>
> Introduce a MEMCG_DMEM stat counter to memory.stat to make the cgroup's
> dmem charge visible.
>
> Signed-off-by: Eric Chanudet <echanude@redhat.com>

Reviewed-by: Albert Esteve <aesteve@redhat.com>

> ---
>  include/linux/memcontrol.h | 16 ++++++++++++
>  mm/memcontrol.c            | 65 ++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 81 insertions(+)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index dc3fa687759b45748b2acee6d7f43da325eb50c1..8e1d49b87fb64e6114f3eb920293e14920290fe7 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -39,6 +39,7 @@ enum memcg_stat_item {
>         MEMCG_ZSWAP_B,
>         MEMCG_ZSWAPPED,
>         MEMCG_ZSWAP_INCOMP,
> +       MEMCG_DMEM,
>         MEMCG_NR_STAT,
>  };
>
> @@ -1872,6 +1873,21 @@ static inline bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg)
>  }
>  #endif
>
> +#if defined(CONFIG_MEMCG) && defined(CONFIG_CGROUP_DMEM)
> +bool mem_cgroup_dmem_charge(struct cgroup *cgrp, unsigned int nr_pages,
> +                           gfp_t gfp_mask);
> +void mem_cgroup_dmem_uncharge(struct cgroup *cgrp, unsigned int nr_pages);
> +#else
> +static inline bool mem_cgroup_dmem_charge(struct cgroup *cgrp,
> +                                         unsigned int nr_pages, gfp_t gfp_mask)
> +{
> +       return true;
> +}
> +static inline void mem_cgroup_dmem_uncharge(struct cgroup *cgrp,
> +                                           unsigned int nr_pages)
> +{
> +}
> +#endif
>
>  /* Cgroup v1-related declarations */
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index c03d4787d466803db49cdaa90e6d6ba426b7afe2..91a7ac16b6eac2d6c3700b6885a068bf8b640706 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -433,6 +433,7 @@ static const unsigned int memcg_stat_items[] = {
>         MEMCG_ZSWAP_B,
>         MEMCG_ZSWAPPED,
>         MEMCG_ZSWAP_INCOMP,
> +       MEMCG_DMEM,
>  };
>
>  #define NR_MEMCG_NODE_STAT_ITEMS ARRAY_SIZE(memcg_node_stat_items)
> @@ -1606,6 +1607,9 @@ static const struct memory_stat memory_stats[] = {
>  #ifdef CONFIG_NUMA_BALANCING
>         { "pgpromote_success",          PGPROMOTE_SUCCESS       },
>  #endif
> +#ifdef CONFIG_CGROUP_DMEM
> +       { "dmem",                       MEMCG_DMEM              },
> +#endif
>  };
>
>  /* The actual unit of the state item, not the same as the output unit */
> @@ -5909,6 +5913,67 @@ static struct cftype zswap_files[] = {
>  };
>  #endif /* CONFIG_ZSWAP */
>
> +#ifdef CONFIG_CGROUP_DMEM
> +/**
> + * mem_cgroup_dmem_charge - charge memcg for a dmem pool allocation
> + * @cgrp: cgroup of the dmem pool
> + * @nr_pages: number of pages to charge
> + * @gfp_mask: reclaim mode
> + *
> + * Charges @nr_pages to @memcg. Returns %true if the charge fit within
> + * @memcg's configured limit, %false if it doesn't.
> + */
> +bool mem_cgroup_dmem_charge(struct cgroup *cgrp, unsigned int nr_pages,
> +                           gfp_t gfp_mask)
> +{
> +       struct cgroup_subsys_state *mem_css;
> +       struct mem_cgroup *memcg;
> +
> +       /* CGROUP_DMEM and MEMCG guarantees this cannot be NULL. */
> +       mem_css = cgroup_get_e_css(cgrp, &memory_cgrp_subsys);
> +
> +       /* Use the memcg, if any, of the dmem cgroup. */
> +       memcg = mem_cgroup_from_css(mem_css);
> +       if (!memcg || mem_cgroup_is_root(memcg)) {
> +               css_put(mem_css);
> +               return false;
> +       }
> +
> +       if (try_charge_memcg(memcg, gfp_mask, nr_pages)) {
> +               css_put(mem_css);
> +               return false;
> +       }
> +
> +       mod_memcg_state(memcg, MEMCG_DMEM, nr_pages);
> +       css_put(mem_css);
> +       return true;
> +}
> +
> +/**
> + * mem_cgroup_dmem_uncharge - uncharge memcg from a dmem pool allocation
> + * @cgrp: cgroup of the dmem pool
> + * @nr_pages: number of pages to uncharge
> + */
> +void mem_cgroup_dmem_uncharge(struct cgroup *cgrp, unsigned int nr_pages)
> +{
> +       struct cgroup_subsys_state *mem_css;
> +       struct mem_cgroup *memcg;
> +
> +       /* CGROUP_DMEM and MEMCG guarantees this cannot be NULL. */
> +       mem_css = cgroup_get_e_css(cgrp, &memory_cgrp_subsys);
> +
> +       memcg = mem_cgroup_from_css(mem_css);
> +       if (!memcg || mem_cgroup_is_root(memcg)) {
> +               css_put(mem_css);
> +               return;
> +       }
> +
> +       mod_memcg_state(memcg, MEMCG_DMEM, -nr_pages);
> +       refill_stock(memcg, nr_pages);
> +       css_put(mem_css);
> +}
> +#endif /* CONFIG_CGROUP_DMEM */
> +
>  static int __init mem_cgroup_swap_init(void)
>  {
>         if (mem_cgroup_disabled())
>
> --
> 2.52.0
>