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

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Date: Fri, 16 Feb 2024 16:49:19 +1300
From: Barry Song <21cnbao@...il.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: davem@...emloft.net, akpm@...ux-foundation.org, ddstreet@...e.org, 
	sjenning@...hat.com, vitaly.wool@...sulko.com, linux-crypto@...r.kernel.org, 
	chriscli@...gle.com, chrisl@...nel.org, hannes@...xchg.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, nphamcs@...il.com, 
	yosryahmed@...gle.com, zhouchengming@...edance.com, 
	Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH 3/3] crypto: scompress: remove memcpy if sg_nents is 1

On Thu, Jan 25, 2024 at 10:58 PM Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> On Wed, Jan 03, 2024 at 10:50:06PM +1300, Barry Song wrote:
> >
> > +     if (dst != scratch->dst)
> > +             kunmap_local(dst);
>
> This is missing a flush_dcache_page.

Thanks, Herbert!  I'd rather add flush_dcache_page()
to the below place so that we can avoid one redundant
flush for ENOSPC/ENOMEM case:

        if (!ret) {
                if (!req->dst) {
                        req->dst = sgl_alloc(req->dlen, GFP_ATOMIC, NULL);
                        if (!req->dst) {
                                ret = -ENOMEM;
                                goto out;
                        }
                } else if (req->dlen > dlen) {
                        ret = -ENOSPC;
                        goto out;
                }
                if (dst == scratch->dst) {
                        scatterwalk_map_and_copy(scratch->dst, req->dst, 0,
                                                 req->dlen, 1);
                } else {
+                        flush_dcache_page(sg_page(req->dst));
                }
        }
out:
        if (src != scratch->src)
                kunmap_local(src);
        if (dst != scratch->dst)
                kunmap_local(dst);

>
> It may not matter for zswap, but this is API code and needs to
> work for every single case.
>
> 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
>

Thanks
Barry