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From: Barry Song <21cnbao@gmail.com>
Date: Fri, 16 Feb 2024 16:49:19 +1300
Message-ID: <CAGsJ_4wf+PF-HVnyARTuAhS4bEe-SZ_pSKzPLp2YQcHp4Aftiw@mail.gmail.com>
Subject: Re: [PATCH 3/3] crypto: scompress: remove memcpy if sg_nents is 1
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: davem@davemloft.net, akpm@linux-foundation.org, ddstreet@ieee.org, 
	sjenning@redhat.com, vitaly.wool@konsulko.com, linux-crypto@vger.kernel.org, 
	chriscli@google.com, chrisl@kernel.org, hannes@cmpxchg.org, 
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, nphamcs@gmail.com, 
	yosryahmed@google.com, zhouchengming@bytedance.com, 
	Barry Song <v-songbaohua@oppo.com>
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On Thu, Jan 25, 2024 at 10:58=E2=80=AFPM Herbert Xu <herbert@gondor.apana.o=
rg.au> wrote:
>
> On Wed, Jan 03, 2024 at 10:50:06PM +1300, Barry Song wrote:
> >
> > +     if (dst !=3D 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 =3D sgl_alloc(req->dlen, GFP_ATOMIC, NULL)=
;
                        if (!req->dst) {
                                ret =3D -ENOMEM;
                                goto out;
                        }
                } else if (req->dlen > dlen) {
                        ret =3D -ENOSPC;
                        goto out;
                }
                if (dst =3D=3D 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 !=3D scratch->src)
                kunmap_local(src);
        if (dst !=3D 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@gondor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
>

Thanks
Barry