linux-kernel - Re: [PATCH v5 3/3] crypto: scompress: remove memcpy if sg

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Message-ID: <ZdWLim6zYSl/x1Bk@gondor.apana.org.au>
Date: Wed, 21 Feb 2024 13:35:06 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org, davem@...emloft.net, hannes@...xchg.org,
	linux-crypto@...r.kernel.org, linux-mm@...ck.org, nphamcs@...il.com,
	yosryahmed@...gle.com, zhouchengming@...edance.com,
	chriscli@...gle.com, chrisl@...nel.org, ddstreet@...e.org,
	linux-kernel@...r.kernel.org, sjenning@...hat.com,
	vitaly.wool@...sulko.com, Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH v5 3/3] crypto: scompress: remove memcpy if sg_nents is 1

On Tue, Feb 20, 2024 at 07:44:14PM +1300, Barry Song wrote:
> From: Barry Song <v-songbaohua@...o.com>
> 
> while sg_nents is 1 which is always true for the current kernel
> as the only user - zswap is the case, we should remove two big
> memcpy.
> 
> Signed-off-by: Barry Song <v-songbaohua@...o.com>
> Tested-by: Chengming Zhou <zhouchengming@...edance.com>
> ---
>  crypto/scompress.c | 36 +++++++++++++++++++++++++++++-------
>  1 file changed, 29 insertions(+), 7 deletions(-)

This patch is independent of the other two.  Please split it
out so I can apply it directly.

> @@ -134,13 +135,25 @@ static int scomp_acomp_comp_decomp(struct acomp_req *req, int dir)
>  	scratch = raw_cpu_ptr(&scomp_scratch);
>  	spin_lock(&scratch->lock);
>  
> -	scatterwalk_map_and_copy(scratch->src, req->src, 0, req->slen, 0);
> +	if (sg_nents(req->src) == 1) {
> +		src = kmap_local_page(sg_page(req->src)) + req->src->offset;

What if the SG entry is longer than PAGE_SIZE (or indeed crosses a
page boundary)? I think the test needs to be strengthened.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt