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Date:   Thu, 7 Jul 2022 23:17:33 +0200
From:   David Sterba <dsterba@suse.cz>
To:     "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
Cc:     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>, Qu Wenruo <wqu@suse.com>,
        Filipe Manana <fdmanana@suse.com>,
        Gabriel Niebler <gniebler@suse.com>,
        linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        Ira Weiny <ira.weiny@intel.com>
Subject: Re: [PATCH] btrfs: Convert zlib_compress_pages() to use
 kmap_local_page()
Message-ID: <20220707211732.GP15169@twin.jikos.cz>
Reply-To: dsterba@suse.cz
Mail-Followup-To: dsterba@suse.cz,
        "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
        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>, Qu Wenruo <wqu@suse.com>,
        Filipe Manana <fdmanana@suse.com>,
        Gabriel Niebler <gniebler@suse.com>, linux-btrfs@vger.kernel.org,
        linux-kernel@vger.kernel.org, Ira Weiny <ira.weiny@intel.com>
References: <20220627163305.24116-1-fmdefrancesco@gmail.com>
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On Mon, Jun 27, 2022 at 06:33:05PM +0200, 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.
> 
> Therefore, use kmap_local_page() / kunmap_local() in zlib_compress_pages()
> because in this function the mappings are per thread and are not visible
> in other contexts. Furthermore, drop the mappings of "out_page" which is
> allocated within zlib_compress_pages() with alloc_page(GFP_NOFS) and use
> page_address() (thanks to David Sterba).
> 
> Tested with xfstests on a QEMU + KVM 32-bits VM with 4GB of RAM booting
> a kernel with HIGHMEM64G enabled. This patch passes 26/26 tests of group
> "compress".
> 
> Cc: Qu Wenruo <wqu@suse.com>
> Suggested-by: David Sterba <dsterba@suse.com>
> Suggested-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>

Added to the kmap patch queue, thanks.