Re: [PATCH v3 10/13] mm: zswap: Add a per-cpu "acomp_batch_ctx" to struct zswap_pool.

[Yosry Ahmed]

On Wed, Nov 6, 2024 at 11:21 AM Kanchana P Sridhar
<kanchana.p.sridhar@xxxxxxxxx> wrote:
>
> This patch adds a separate per-cpu batching acomp context "acomp_batch_ctx"
> to the zswap_pool. The per-cpu acomp_batch_ctx pointer is allocated at pool
> creation time, but no per-cpu resources are allocated for it.
>
> The idea is to not incur the memory footprint cost of multiple acomp_reqs
> and buffers in the existing "acomp_ctx" for cases where compress batching
> is not possible; for instance, with software compressor algorithms, on
> systems without IAA, on systems with IAA that want to run the existing
> non-batching implementation of zswap_store() of large folios.
>
> By creating a separate acomp_batch_ctx, we have the ability to allocate
> additional memory per-cpu only if the zswap compressor supports batching,
> and if the user wants to enable the use of compress batching in
> zswap_store() to improve swapout performance of large folios.
>
> Suggested-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>

This isn't needed if the sysctl is removed and we just allocate the
number of buffers during pool initialization, right? Same for the next
patch.


> Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx>
> ---
>  mm/zswap.c | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 02e031122fdf..80a928cf0f7e 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -160,6 +160,7 @@ struct crypto_acomp_ctx {
>  struct zswap_pool {
>         struct zpool *zpool;
>         struct crypto_acomp_ctx __percpu *acomp_ctx;
> +       struct crypto_acomp_ctx __percpu *acomp_batch_ctx;
>         struct percpu_ref ref;
>         struct list_head list;
>         struct work_struct release_work;
> @@ -287,10 +288,14 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
>
>         pool->acomp_ctx = alloc_percpu(*pool->acomp_ctx);
>         if (!pool->acomp_ctx) {
> -               pr_err("percpu alloc failed\n");
> +               pr_err("percpu acomp_ctx alloc failed\n");
>                 goto error;
>         }
>
> +       pool->acomp_batch_ctx = alloc_percpu(*pool->acomp_batch_ctx);
> +       if (!pool->acomp_batch_ctx)
> +               pr_err("percpu acomp_batch_ctx alloc failed\n");
> +
>         ret = cpuhp_state_add_instance(CPUHP_MM_ZSWP_POOL_PREPARE,
>                                        &pool->node);
>         if (ret)
> @@ -312,6 +317,8 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
>  ref_fail:
>         cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
>  error:
> +       if (pool->acomp_batch_ctx)
> +               free_percpu(pool->acomp_batch_ctx);
>         if (pool->acomp_ctx)
>                 free_percpu(pool->acomp_ctx);
>         if (pool->zpool)
> @@ -368,6 +375,8 @@ static void zswap_pool_destroy(struct zswap_pool *pool)
>
>         cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
>         free_percpu(pool->acomp_ctx);
> +       if (pool->acomp_batch_ctx)
> +               free_percpu(pool->acomp_batch_ctx);
>
>         zpool_destroy_pool(pool->zpool);
>         kfree(pool);
> @@ -930,6 +939,11 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
>         struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
>         struct crypto_acomp_ctx *acomp_ctx;
>
> +       if (pool->acomp_batch_ctx) {
> +               acomp_ctx = per_cpu_ptr(pool->acomp_batch_ctx, cpu);
> +               acomp_ctx->nr_reqs = 0;
> +       }
> +
>         acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);
>         return zswap_create_acomp_ctx(cpu, acomp_ctx, pool->tfm_name, 1);
>  }
> @@ -939,6 +953,12 @@ static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node)
>         struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
>         struct crypto_acomp_ctx *acomp_ctx;
>
> +       if (pool->acomp_batch_ctx) {
> +               acomp_ctx = per_cpu_ptr(pool->acomp_batch_ctx, cpu);
> +               if (!IS_ERR_OR_NULL(acomp_ctx) && (acomp_ctx->nr_reqs > 0))
> +                       zswap_delete_acomp_ctx(acomp_ctx);
> +       }
> +
>         acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);
>         zswap_delete_acomp_ctx(acomp_ctx);
>
> --
> 2.27.0
>