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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     David Sterba <dsterba@suse.com>
Cc:     Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
        Nick Terrell <terrelln@fb.com>,
        Chris Down <chris@chrisdown.name>,
        Filipe Manana <fdmanana@suse.com>, Qu Wenruo <wqu@suse.com>,
        Nikolay Borisov <nborisov@suse.com>,
        Gabriel Niebler <gniebler@suse.com>,
        Ira Weiny <ira.weiny@intel.com>, linux-btrfs@vger.kernel.org,
        linux-kernel@vger.kernel.org, David Sterba <dsterba@suse.cz>
Subject: Re: [RFC PATCH] btrfs: Replace kmap_atomic() with kmap_local_page()
Date:   Mon, 27 Jun 2022 20:01:31 +0200
Message-ID: <8960694.CDJkKcVGEf@opensuse>
In-Reply-To: <20220624084215.7287-1-fmdefrancesco@gmail.com>
References: <20220624084215.7287-1-fmdefrancesco@gmail.com>
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On venerd=C3=AC 24 giugno 2022 10:42:15 CEST Fabio M. De Francesco wrote:
> kmap_atomic() is being deprecated in favor of kmap_local_page() where it
> is feasible. With kmap_local_page() mappings are per thread, CPU local,
> and not globally visible.
>=20
> As far as I can see, the kmap_atomic() calls in compression.c and in
> inode.c can be safely converted.
>=20
> Above all else, David Sterba has confirmed that "The context in
> check_compressed_csum is atomic [...]" and that "kmap_atomic() in inode.c
> [...] also can be replaced by kmap_local_page().".[1]
>=20
> Therefore, convert all kmap_atomic() calls currently still left in fs/
btrfs
> to kmap_local_page().
>=20
> This is an RFC only because, testing with "./check -g quick" (xfstests)=20
on
> a QEMU + KVM 32-bits VM with 4GB RAM and booting a kernel with=20
HIGHMEM64GB
> enabled, outputs several errors. These errors seem to be exactly the same
> which are being output without this patch. It apparently seems that these
> changes don't introduce further errors, however I'd like to ask for
> comments before sending a "real" patch.
>=20
> With this patch, there are no more call sites for kmap() and=20
kmap_atomic()
> in fs/btrfs.
>=20
> [1] https://lore.kernel.org/linux-btrfs/
20220601132545.GM20633@twin.jikos.cz/
>=20
> Suggested-by: Ira Weiny <ira.weiny@intel.com>
> Suggested-by: David Sterba <dsterba@suse.cz>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
>  fs/btrfs/compression.c |  4 ++--
>  fs/btrfs/inode.c       | 12 ++++++------
>  2 files changed, 8 insertions(+), 8 deletions(-)
>=20

Please discard this RFC.

I've just submitted a real patch:

https://lore.kernel.org/lkml/20220627174849.29962-1-fmdefrancesco@gmail.com/

Thanks,

=46abio