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

[Yosry Ahmed <yosry@kernel.org>]

> 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.

I like this.

I also didn't like the suggested prototype for zs_create_pool(), and
didn't like that compressed_stat and uncompressed_stat did not have
memcg anywhere in the name. Was going to suggest adding a warning if
memcg_aware=false but the stat indices are non-zero, but your
suggestion is so much cleaner.