Re: [PATCH v7] crypto: scompress: remove memcpy if sg_nents is 1 and pages are lowmem

From: Guenter Roeck <linux@roeck-us.net>
To: Barry Song <21cnbao@gmail.com>
Cc: herbert@gondor.apana.org.au, davem@davemloft.net,
	linux-crypto@vger.kernel.org, akpm@linux-foundation.org,
	chrisl@kernel.org, sjenning@redhat.com, vitaly.wool@konsulko.com,
	linux-kernel@vger.kernel.org, Barry Song <v-songbaohua@oppo.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Nhat Pham <nphamcs@gmail.com>,
	Yosry Ahmed <yosryahmed@google.com>,
	Chengming Zhou <zhouchengming@bytedance.com>
Subject: Re: [PATCH v7] crypto: scompress: remove memcpy if sg_nents is 1 and pages are lowmem
Date: Sun, 17 Mar 2024 16:13:47 -0700	[thread overview]
Message-ID: <aaa8b7d7-5abe-47bf-93f6-407942436472@roeck-us.net> (raw)
In-Reply-To: <20240301192745.14987-1-21cnbao@gmail.com>

Hi,

On Sat, Mar 02, 2024 at 08:27:45AM +1300, Barry Song wrote:
[ ... ]
> @@ -152,8 +165,17 @@ static int scomp_acomp_comp_decomp(struct acomp_req *req, int dir)
>  			ret = -ENOSPC;
>  			goto out;
>  		}
> -		scatterwalk_map_and_copy(scratch->dst, req->dst, 0, req->dlen,
> -					 1);
> +		if (dst == scratch->dst) {
> +			scatterwalk_map_and_copy(scratch->dst, req->dst, 0,
> +						 req->dlen, 1);
> +		} else {
> +			int nr_pages = DIV_ROUND_UP(req->dst->offset + req->dlen, PAGE_SIZE);
> +			int i;
> +			struct page *dst_page = sg_page(req->dst);
> +
> +			for (i = 0; i < nr_pages; i++)
> +				flush_dcache_page(dst_page + i);

flush_dcache_page() is an empty macro on some architectures
such as xtensa. This results in

Building xtensa:allmodconfig ... failed
--------------
Error log:
crypto/scompress.c: In function 'scomp_acomp_comp_decomp':
crypto/scompress.c:174:38: error: unused variable 'dst_page'

on the affected architectures.

Guenter