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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     =?ISO-8859-1?Q?J=E9r=F4me?= Glisse <jglisse@redhat.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Sumitra Sharma <sumitraartsy@gmail.com>
Cc:     Ira Weiny <ira.weiny@intel.com>, Deepak R Varma <drv@mailo.com>
Subject: Re: [PATCH v2] lib: Replace kmap() with kmap_local_page()
Date:   Sun, 18 Jun 2023 06:50:04 +0200
Message-ID: <8275009.NyiUUSuA9g@suse>
In-Reply-To: <20230610175712.GA348514@sumitra.com>
References: <20230610175712.GA348514@sumitra.com>
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On sabato 10 giugno 2023 19:57:12 CEST Sumitra Sharma wrote:
> kmap() has been deprecated in favor of the kmap_local_page()
> due to high cost, restricted mapping space, the overhead of
> a global lock for synchronization, and making the process
> sleep in the absence of free slots.
>=20
> kmap_local_page() is faster than kmap() and offers thread-local
> and CPU-local mappings, take pagefaults in a local kmap region
> and preserves preemption by saving the mappings of outgoing
> tasks and restoring those of the incoming one during a context
> switch.
>=20
> The mappings are kept thread local in the functions
> =E2=80=9Cdmirror_do_read=E2=80=9D and =E2=80=9Cdmirror_do_write=E2=80=9D =
in test_hmm.c
>=20
> Therefore, replace kmap() with kmap_local_page() and use
> mempcy_from/to_page() to avoid open coding kmap_local_page()
> + memcpy() + kunmap_local().
>=20
> Remove the unused variable =E2=80=9Ctmp=E2=80=9D.
>=20
>=20
> Suggested-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>

LGTM, so...

Reviewed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>

Thanks,

=46abio

P.S.: The answer to an old question from you is that "LGTM" stands for "[It=
]=20
Looks Good To Me".=20

It's just a way to introduce the "Reviewed-by" tag itself. However, "LGTM" =
is=20
not required, whereas the tag is required for a valid review and only the t=
ag=20
line will be added by maintainers in the log when your patch gets applied. =
=20

While here... Please don't put unnecessary blank lines between the tags.The=
y=20
are not required and instead may worsen readability (obviously, I'm not=20
requiring a new version for this). =20

>=20
> Signed-off-by: Sumitra Sharma <sumitraartsy@gmail.com>
> ---
>=20
> Changes in v2:
> 	- Change commit subject and description.
> 	- Remove unnecessary type casting (char *).
>=20
>=20
>  lib/test_hmm.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
>=20
> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
> index 67e6f83fe0f8..717dcb830127 100644
> --- a/lib/test_hmm.c
> +++ b/lib/test_hmm.c
> @@ -368,16 +368,13 @@ static int dmirror_do_read(struct dmirror *dmirror,
> unsigned long start, for (pfn =3D start >> PAGE_SHIFT; pfn < (end >>
> PAGE_SHIFT); pfn++) { void *entry;
>  		struct page *page;
> -		void *tmp;
>=20
>  		entry =3D xa_load(&dmirror->pt, pfn);
>  		page =3D xa_untag_pointer(entry);
>  		if (!page)
>  			return -ENOENT;
>=20
> -		tmp =3D kmap(page);
> -		memcpy(ptr, tmp, PAGE_SIZE);
> -		kunmap(page);
> +		memcpy_from_page(ptr, page, 0, PAGE_SIZE);
>=20
>  		ptr +=3D PAGE_SIZE;
>  		bounce->cpages++;
> @@ -437,16 +434,13 @@ static int dmirror_do_write(struct dmirror *dmirror,
> unsigned long start, for (pfn =3D start >> PAGE_SHIFT; pfn < (end >>
> PAGE_SHIFT); pfn++) { void *entry;
>  		struct page *page;
> -		void *tmp;
>=20
>  		entry =3D xa_load(&dmirror->pt, pfn);
>  		page =3D xa_untag_pointer(entry);
>  		if (!page || xa_pointer_tag(entry) !=3D DPT_XA_TAG_WRITE)
>  			return -ENOENT;
>=20
> -		tmp =3D kmap(page);
> -		memcpy(tmp, ptr, PAGE_SIZE);
> -		kunmap(page);
> +		memcpy_to_page(page, 0, ptr, PAGE_SIZE);
>=20
>  		ptr +=3D PAGE_SIZE;
>  		bounce->cpages++;
> --
> 2.25.1