Re: [PATCH 04/11] mm/zsmalloc: Introduce objcgs pointer in struct zspage

[Nhat Pham]

On Wed, Mar 11, 2026 at 12:52 PM Joshua Hahn <joshua.hahnjy@xxxxxxxxx> wrote:
>
> Introduce an array of struct obj_cgroup pointers to zspage to keep track
> of compressed objects' memcg ownership, if the zs_pool has been made to
> be memcg-aware at creation time.
>
> Move the error path for alloc_zspage to a jump label to simplify the
> growing error handling path for a failed zpdesc allocation.
>
> Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Suggested-by: Harry Yoo <harry.yoo@xxxxxxxxxx>
> Signed-off-by: Joshua Hahn <joshua.hahnjy@xxxxxxxxx>
> ---
>  mm/zsmalloc.c | 34 ++++++++++++++++++++++++++--------
>  1 file changed, 26 insertions(+), 8 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 3f0f42b78314..dcf99516227c 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -39,6 +39,7 @@
>  #include <linux/zsmalloc.h>
>  #include <linux/fs.h>
>  #include <linux/workqueue.h>
> +#include <linux/memcontrol.h>
>  #include "zpdesc.h"
>
>  #define ZSPAGE_MAGIC   0x58
> @@ -273,6 +274,7 @@ struct zspage {
>         struct zpdesc *first_zpdesc;
>         struct list_head list; /* fullness list */
>         struct zs_pool *pool;
> +       struct obj_cgroup **objcgs;
>         struct zspage_lock zsl;
>  };
>
> @@ -825,6 +827,8 @@ static void __free_zspage(struct zs_pool *pool, struct size_class *class,
>                 zpdesc = next;
>         } while (zpdesc != NULL);
>
> +       if (pool->memcg_aware)
> +               kfree(zspage->objcgs);
>         cache_free_zspage(zspage);
>
>         class_stat_sub(class, ZS_OBJS_ALLOCATED, class->objs_per_zspage);
> @@ -946,6 +950,16 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
>         if (!IS_ENABLED(CONFIG_COMPACTION))
>                 gfp &= ~__GFP_MOVABLE;
>
> +       if (pool->memcg_aware) {
> +               zspage->objcgs = kcalloc(class->objs_per_zspage,
> +                                        sizeof(struct obj_cgroup *),
> +                                        gfp & ~__GFP_HIGHMEM);

I remembered asking this, so my apologies if I missed/forgot your
response - but would vmalloc work here? i.e kvcalloc to fallback to
vmalloc etc.?

> +               if (!zspage->objcgs) {
> +                       cache_free_zspage(zspage);
> +                       return NULL;
> +               }
> +       }
> +
>         zspage->magic = ZSPAGE_MAGIC;
>         zspage->pool = pool;
>         zspage->class = class->index;
> @@ -955,14 +969,8 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
>                 struct zpdesc *zpdesc;
>
>                 zpdesc = alloc_zpdesc(gfp, nid);
> -               if (!zpdesc) {
> -                       while (--i >= 0) {
> -                               zpdesc_dec_zone_page_state(zpdescs[i]);
> -                               free_zpdesc(zpdescs[i]);
> -                       }
> -                       cache_free_zspage(zspage);
> -                       return NULL;
> -               }
> +               if (!zpdesc)
> +                       goto err;
>                 __zpdesc_set_zsmalloc(zpdesc);
>
>                 zpdesc_inc_zone_page_state(zpdesc);
> @@ -973,6 +981,16 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
>         init_zspage(class, zspage);
>
>         return zspage;
> +
> +err:
> +       while (--i >= 0) {
> +               zpdesc_dec_zone_page_state(zpdescs[i]);
> +               free_zpdesc(zpdescs[i]);
> +       }
> +       if (pool->memcg_aware)
> +               kfree(zspage->objcgs);
> +       cache_free_zspage(zspage);
> +       return NULL;
>  }
>
>  static struct zspage *find_get_zspage(struct size_class *class)
> --
> 2.52.0
>