Re: [RFC PATCH 7/7] mm: zswap: Use acomp virtual address interface

[Yosry Ahmed <yosry.ahmed@linux.dev>]

On Thu, Feb 27, 2025 at 06:15:09PM +0800, Herbert Xu wrote:
> Use the acomp virtual address interface.
> 
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

I can't speak to the rest of the series, but I like what this patch is
doing in zswap. Together with the recent zsmalloc changes, we should be
able to drop the alternative memcpy path completely, without needing to
use kmap_to_page() or removing the warning the highmem code.

Thanks for doing this!

> ---
>  mm/zswap.c | 23 ++++++++---------------
>  1 file changed, 8 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 6504174fbc6a..2b5a2398a9be 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -925,27 +925,20 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
>  			   struct zswap_pool *pool)
>  {
>  	struct crypto_acomp_ctx *acomp_ctx;
> -	struct scatterlist input, output;
>  	int comp_ret = 0, alloc_ret = 0;
>  	unsigned int dlen = PAGE_SIZE;
>  	unsigned long handle;
>  	struct zpool *zpool;
> +	const u8 *src;
>  	char *buf;
>  	gfp_t gfp;
>  	u8 *dst;
>  
>  	acomp_ctx = acomp_ctx_get_cpu_lock(pool);
> +	src = kmap_local_page(page);
>  	dst = acomp_ctx->buffer;
> -	sg_init_table(&input, 1);
> -	sg_set_page(&input, page, PAGE_SIZE, 0);
>  
> -	/*
> -	 * We need PAGE_SIZE * 2 here since there maybe over-compression case,
> -	 * and hardware-accelerators may won't check the dst buffer size, so
> -	 * giving the dst buffer with enough length to avoid buffer overflow.
> -	 */
> -	sg_init_one(&output, dst, PAGE_SIZE * 2);
> -	acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen);
> +	acomp_request_set_virt(acomp_ctx->req, src, dst, PAGE_SIZE, dlen);
>  
>  	/*
>  	 * it maybe looks a little bit silly that we send an asynchronous request,
> @@ -960,6 +953,7 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
>  	 * acomp instance, so multiple threads can do (de)compression in parallel.
>  	 */
>  	comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
> +	kunmap_local(src);
>  	dlen = acomp_ctx->req->dlen;
>  	if (comp_ret)
>  		goto unlock;
> @@ -994,9 +988,9 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
>  static void zswap_decompress(struct zswap_entry *entry, struct folio *folio)
>  {
>  	struct zpool *zpool = entry->pool->zpool;
> -	struct scatterlist input, output;
>  	struct crypto_acomp_ctx *acomp_ctx;
>  	u8 *src;
> +	u8 *dst;
>  
>  	acomp_ctx = acomp_ctx_get_cpu_lock(entry->pool);
>  	src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
> @@ -1016,11 +1010,10 @@ static void zswap_decompress(struct zswap_entry *entry, struct folio *folio)
>  		zpool_unmap_handle(zpool, entry->handle);
>  	}
>  
> -	sg_init_one(&input, src, entry->length);
> -	sg_init_table(&output, 1);
> -	sg_set_folio(&output, folio, PAGE_SIZE, 0);
> -	acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, PAGE_SIZE);
> +	dst = kmap_local_folio(folio, 0);
> +	acomp_request_set_virt(acomp_ctx->req, src, dst, entry->length, PAGE_SIZE);
>  	BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait));
> +	kunmap_local(dst);
>  	BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
>  
>  	if (src != acomp_ctx->buffer)
> -- 
> 2.39.5
>