Message-ID: <CAGsJ_4xRij-Vz_-dmL44YLvaQrYLKKnw7O_Skedrxj_YxuaT5Q@mail.gmail.com>
Date: Tue, 26 Aug 2025 11:48:08 +0800
From: Barry Song <21cnbao@...il.com>
To: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, hannes@...xchg.org, 
	yosry.ahmed@...ux.dev, nphamcs@...il.com, chengming.zhou@...ux.dev, 
	usamaarif642@...il.com, ryan.roberts@....com, ying.huang@...ux.alibaba.com, 
	akpm@...ux-foundation.org, senozhatsky@...omium.org, 
	linux-crypto@...r.kernel.org, herbert@...dor.apana.org.au, 
	davem@...emloft.net, clabbe@...libre.com, ardb@...nel.org, 
	ebiggers@...gle.com, surenb@...gle.com, kristen.c.accardi@...el.com, 
	vinicius.gomes@...el.com, wajdi.k.feghali@...el.com, vinodh.gopal@...el.com
Subject: Re: [PATCH v11 22/24] mm: zswap: Allocate pool batching resources if
 the compressor supports batching.

Hi Kanchana,


[...]
>
> +       /*
> +        * Set the unit of compress batching for large folios, for quick
> +        * retrieval in the zswap_compress() fast path:
> +        * If the compressor is sequential (@pool->compr_batch_size is 1),
> +        * large folios will be compressed in batches of ZSWAP_MAX_BATCH_SIZE
> +        * pages, where each page in the batch is compressed sequentially.
> +        * We see better performance by processing the folio in batches of
> +        * ZSWAP_MAX_BATCH_SIZE, due to cache locality of working set
> +        * structures.
> +        */
> +       pool->batch_size = (pool->compr_batch_size > 1) ?
> +                               pool->compr_batch_size : ZSWAP_MAX_BATCH_SIZE;
> +
>         zswap_pool_debug("created", pool);
>
>         return pool;
>

It’s hard to follow — you add batch_size and compr_batch_size in this
patch, but only use them in another. Could we merge the related changes
into one patch instead of splitting them into several that don’t work
independently?

> -
>         acomp_ctx->acomp = crypto_alloc_acomp_node(pool->tfm_name, 0, 0, cpu_to_node(cpu));
>         if (IS_ERR_OR_NULL(acomp_ctx->acomp)) {
>                 pr_err("could not alloc crypto acomp %s : %ld\n",
> @@ -904,17 +929,36 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
>         acomp_ctx->req = acomp_request_alloc(acomp_ctx->acomp);
>         if (IS_ERR_OR_NULL(acomp_ctx->req)) {
>                 pr_err("could not alloc crypto acomp_request %s\n",
> -                      pool->tfm_name);
> +                       pool->tfm_name);
>                 goto fail;
>         }
>
> -       crypto_init_wait(&acomp_ctx->wait);
> +       /*
> +        * Allocate up to ZSWAP_MAX_BATCH_SIZE dst buffers if the
> +        * compressor supports batching.
> +        */
> +       pool->compr_batch_size = min(ZSWAP_MAX_BATCH_SIZE,
> +                                    crypto_acomp_batch_size(acomp_ctx->acomp));
> +
> +       acomp_ctx->buffers = kcalloc_node(pool->compr_batch_size, sizeof(u8 *),
> +                                         GFP_KERNEL, cpu_to_node(cpu));
> +       if (!acomp_ctx->buffers)
> +               goto fail;
> +
> +       for (i = 0; i < pool->compr_batch_size; ++i) {
> +               acomp_ctx->buffers[i] = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL,
> +                                                    cpu_to_node(cpu));
> +               if (!acomp_ctx->buffers[i])
> +                       goto fail;
> +       }

It’s hard to follow — memory is allocated here but only used in another
patch. Could we merge the related changes into a single patch instead of
splitting them into several that don’t work independently?

>
>         /*
>          * if the backend of acomp is async zip, crypto_req_done() will wakeup
>          * crypto_wait_req(); if the backend of acomp is scomp, the callback
>          * won't be called, crypto_wait_req() will return without blocking.
>          */
> +       crypto_init_wait(&acomp_ctx->wait);
> +
>         acomp_request_set_callback(acomp_ctx->req, CRYPTO_TFM_REQ_MAY_BACKLOG,
>                                    crypto_req_done, &acomp_ctx->wait);
>
> @@ -922,7 +966,7 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
>         return 0;
>
>  fail:
> -       acomp_ctx_dealloc(acomp_ctx);
> +       acomp_ctx_dealloc(acomp_ctx, pool->compr_batch_size);
>         return ret;
>  }
>
> @@ -942,7 +986,7 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
>
>         mutex_lock(&acomp_ctx->mutex);
>
> -       dst = acomp_ctx->buffer;
> +       dst = acomp_ctx->buffers[0];
>         sg_init_table(&input, 1);
>         sg_set_page(&input, page, PAGE_SIZE, 0);
>
> @@ -1003,19 +1047,19 @@ static bool zswap_decompress(struct zswap_entry *entry, struct folio *folio)
>
>         acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
>         mutex_lock(&acomp_ctx->mutex);
> -       obj = zpool_obj_read_begin(zpool, entry->handle, acomp_ctx->buffer);
> +       obj = zpool_obj_read_begin(zpool, entry->handle, acomp_ctx->buffers[0]);
>
>         /*
>          * zpool_obj_read_begin() might return a kmap address of highmem when
> -        * acomp_ctx->buffer is not used.  However, sg_init_one() does not
> -        * handle highmem addresses, so copy the object to acomp_ctx->buffer.
> +        * acomp_ctx->buffers[0] is not used.  However, sg_init_one() does not
> +        * handle highmem addresses, so copy the object to acomp_ctx->buffers[0].
>          */
>         if (virt_addr_valid(obj)) {
>                 src = obj;
>         } else {
> -               WARN_ON_ONCE(obj == acomp_ctx->buffer);
> -               memcpy(acomp_ctx->buffer, obj, entry->length);
> -               src = acomp_ctx->buffer;
> +               WARN_ON_ONCE(obj == acomp_ctx->buffers[0]);
> +               memcpy(acomp_ctx->buffers[0], obj, entry->length);
> +               src = acomp_ctx->buffers[0];

Hard to understand what is going on if related changes are not kept in
one self-contained patch.

Thanks
Barry

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