Re: [PATCH 03/11] mm/zsmalloc: Introduce conditional memcg awareness to zs_pool

[Johannes Weiner <hannes@cmpxchg.org>]

On Wed, Mar 11, 2026 at 12:51:40PM -0700, Joshua Hahn wrote:
> Introduce 3 new fields to struct zs_pool to allow individual zpools to
> be "memcg-aware": memcg_aware, compressed_stat, and uncompressed_stat.
> 
> memcg_aware is used in later patches to determine whether memory
> should be allocated to keep track of per-compresed object objgs.
> compressed_stat and uncompressed_stat are enum indices that point into
> memcg (node) stats that zsmalloc will account towards.
> 
> In reality, these fields help distinguish between the two users of
> zsmalloc, zswap and zram. The enum indices compressed_stat and
> uncompressed_stat are parametrized to minimize zswap-specific hardcoding
> in zsmalloc.
> 
> Suggested-by: Yosry Ahmed <yosry@kernel.org>
> Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
> ---
>  drivers/block/zram/zram_drv.c |  3 ++-
>  include/linux/zsmalloc.h      |  5 ++++-
>  mm/zsmalloc.c                 | 13 ++++++++++++-
>  mm/zswap.c                    |  3 ++-
>  4 files changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index bca33403fc8b..d1eae5c20df7 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1980,7 +1980,8 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize)
>  	if (!zram->table)
>  		return false;
>  
> -	zram->mem_pool = zs_create_pool(zram->disk->disk_name);
> +	/* zram does not support memcg accounting */
> +	zram->mem_pool = zs_create_pool(zram->disk->disk_name, false, 0, 0);

It's a bit awkward that 0 is valid (MEMCG_SWAP). Plus you store these
values in every pool, even though they're always the same for all
zswap pools.

How about:

/* zsmalloc.h */
struct zs_memcg_params {
	enum memcg_stat_item compressed;
	enum memcg_stat_item uncompressed;
};
struct zs_pool *zs_create_pool(const char *name, struct zs_memcg_params *memcg_params);

/* zswap.c */
static struct zs_memcg_params zswap_memcg_params = {
	.compressed = MEMCG_ZSWAP_B,
	.uncompressed = MEMCG_ZSWAPPED,
};

then pass &zswap_memcg_params from zswap and NULL from zram.

> @@ -2071,6 +2079,9 @@ struct zs_pool *zs_create_pool(const char *name)
>  	rwlock_init(&pool->lock);
>  	atomic_set(&pool->compaction_in_progress, 0);
>  
> +	pool->memcg_aware = memcg_aware;
> +	pool->compressed_stat = compressed_stat;
> +	pool->uncompressed_stat = uncompressed_stat;

	pool->memcg_params = memcg_params;

And then use if (pool->memcg_params) to gate in zsmalloc.c.