Re: [PATCH 08/11] mm/memcontrol: Track MEMCG_ZSWAPPED in bytes

[Nhat Pham]

On Wed, Mar 11, 2026 at 12:52 PM Joshua Hahn <joshua.hahnjy@xxxxxxxxx> wrote:
>
> Zswap compresses and uncompresses in PAGE_SIZE units, which simplifies
> the accounting for how much memory it has compressed. However, when a
> compressed object is stored at the boundary of two zspages, accounting
> at a PAGE_SIZE granularity makes it difficult to fractionally charge
> each backing zspage with the ratio of memory it backs for the
> compressed object.
>
> To make sub-PAGE_SIZE granularity charging possible for MEMCG_ZSWAPPED,
> track the value in bytes and adjust its accounting accordingly.
>
> No functional changes intended.
>
> Signed-off-by: Joshua Hahn <joshua.hahnjy@xxxxxxxxx>

LGTM.
Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>

> ---
>  include/linux/memcontrol.h | 2 +-
>  mm/memcontrol.c            | 5 +++--
>  mm/zsmalloc.c              | 4 ++--
>  mm/zswap.c                 | 8 +++++---
>  4 files changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 701d9ab6fef1..ce2e598b5963 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -38,7 +38,7 @@ enum memcg_stat_item {
>         MEMCG_VMALLOC,
>         MEMCG_KMEM,
>         MEMCG_ZSWAP_B,
> -       MEMCG_ZSWAPPED,
> +       MEMCG_ZSWAPPED_B,
>         MEMCG_NR_STAT,
>  };
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 68139be66a4f..1cb02d2febe8 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -342,7 +342,7 @@ static const unsigned int memcg_stat_items[] = {
>         MEMCG_VMALLOC,
>         MEMCG_KMEM,
>         MEMCG_ZSWAP_B,
> -       MEMCG_ZSWAPPED,
> +       MEMCG_ZSWAPPED_B,
>  };
>
>  #define NR_MEMCG_NODE_STAT_ITEMS ARRAY_SIZE(memcg_node_stat_items)
> @@ -1364,7 +1364,7 @@ static const struct memory_stat memory_stats[] = {
>         { "shmem",                      NR_SHMEM                        },
>  #ifdef CONFIG_ZSWAP
>         { "zswap",                      MEMCG_ZSWAP_B                   },
> -       { "zswapped",                   MEMCG_ZSWAPPED                  },
> +       { "zswapped",                   MEMCG_ZSWAPPED_B                },
>  #endif
>         { "file_mapped",                NR_FILE_MAPPED                  },
>         { "file_dirty",                 NR_FILE_DIRTY                   },
> @@ -1412,6 +1412,7 @@ static int memcg_page_state_unit(int item)
>         switch (item) {
>         case MEMCG_PERCPU_B:
>         case MEMCG_ZSWAP_B:
> +       case MEMCG_ZSWAPPED_B:
>         case NR_SLAB_RECLAIMABLE_B:
>         case NR_SLAB_UNRECLAIMABLE_B:
>                 return 1;
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 291194572a09..24665d7cd4a9 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1047,7 +1047,7 @@ static void zs_charge_objcg(struct zs_pool *pool, struct obj_cgroup *objcg,
>         rcu_read_lock();
>         memcg = obj_cgroup_memcg(objcg);
>         mod_memcg_state(memcg, pool->compressed_stat, size);
> -       mod_memcg_state(memcg, pool->uncompressed_stat, 1);
> +       mod_memcg_state(memcg, pool->uncompressed_stat, PAGE_SIZE);
>         rcu_read_unlock();
>  }
>
> @@ -1066,7 +1066,7 @@ static void zs_uncharge_objcg(struct zs_pool *pool, struct obj_cgroup *objcg,
>         rcu_read_lock();
>         memcg = obj_cgroup_memcg(objcg);
>         mod_memcg_state(memcg, pool->compressed_stat, -size);
> -       mod_memcg_state(memcg, pool->uncompressed_stat, -1);
> +       mod_memcg_state(memcg, pool->uncompressed_stat, -(int)PAGE_SIZE);

nit: seems a bit awkward lol?