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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.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>,
        linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Ira Weiny <ira.weiny@intel.com>
Subject: Re: [RFC PATCH] btrfs: Replace kmap() with kmap_local_page() in zlib.c
Date:   Fri, 17 Jun 2022 14:18:23 +0200
Message-ID: <2243807.ElGaqSPkdT@opensuse>
In-Reply-To: <20220614104718.9193-1-fmdefrancesco@gmail.com>
References: <20220614104718.9193-1-fmdefrancesco@gmail.com>
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On marted=C3=AC 14 giugno 2022 12:47:18 CEST Fabio M. De Francesco wrote:
> The use of kmap() is being deprecated in favor of kmap_local_page(). With
> kmap_local_page(), the mapping is per thread, CPU local and not globally
> visible.
>=20
> Therefore, use kmap_local_page() / kunmap_local() in zlib.c because in
> this file the mappings are per thread and are not visible in other
> contexts; meanwhile refactor zlib_compress_pages() to comply with nested
> local mapping / unmapping ordering rules.
>=20
> Tested with xfstests on QEMU + KVM 32 bits VM with 4GB of RAM and
> HIGHMEM64G enabled.
>=20
> This is an RFC PATCH because it passes all tests of the "compress"
> group, with the only two exceptions of tests/btrfs/138 (it freezes the
> VM) and tests/btrfs/251 (it runs forever but doesn't freeze the VM).
>=20
> Can anyone please take a look and tell me what I'm still overlooking
> after days of code inspections?
>=20
> Suggested-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
>  fs/btrfs/zlib.c | 75 ++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 50 insertions(+), 25 deletions(-)
>=20
Please don't respond to this RFC and drop it. I've just split it into three=
=20
new versions and send a series of RFC PATCH(es) which seems to work=20
properly.=20

They can pass all tests of the group "compress", but I decided to implement=
=20
some questionable solutions. Therefore, I'd like to hear about them:

https://lore.kernel.org/lkml/20220617120538.18091-1-fmdefrancesco@gmail.com=
/T/#t

Thanks,

=46abio