Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 30 Jun 2022 07:51:14 -0700
From:   Ira Weiny <ira.weiny@intel.com>
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>
Subject: Re: [PATCH] btrfs: Convert zlib_compress_pages() to use
 kmap_local_page()
Message-ID: <Yr24YtEM9JyHp+jS@iweiny-desk3>
References: <20220627163305.24116-1-fmdefrancesco@gmail.com>
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <20220627163305.24116-1-fmdefrancesco@gmail.com>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?ZUGC7SDO1/txYAnzJNTnOuKQXq7/t3danzCKI2M7sJVjNF2ZG1CGXimjItJz?=
 =?us-ascii?Q?nKi+V4GcY0c/AxwTcEJV8mFB/xrctTNDynVT1w7zZ/qFqzxX0vM0Tyroa6/k?=
 =?us-ascii?Q?/ux+nsSbQyzT19gzY+nMx5qCj9Rf2piNN7EWO2NLfiz46/F2vjZURcCG7yuI?=
 =?us-ascii?Q?Uvg5Mklu1FH54zhX/C2O/JNF9eVTIiPrDsjqWVdHdqeBbMnoQv7TuEE8FcaV?=
 =?us-ascii?Q?4kyUspMVWP/l+BpohtqlahrFOvZ1dXxnsbQuFmxZd0JRDjCK19lu4A7Z8a8l?=
 =?us-ascii?Q?E3paGvFDU4ruHlxkZX+sMvs8G3hDXahY8MKK9vBpslNcg+WigfOLsIC26C9y?=
 =?us-ascii?Q?zKaitVxDEqVsbecZNElX+GaEm+1NmQRgTDn4z5LBEHB03qlylq5GedgMduD6?=
 =?us-ascii?Q?u4m5y9KQopCJbIBAsq2Hmvss5peImQCSt3TesYA4h4orC/wVsCaJHZDh4H1s?=
 =?us-ascii?Q?neCKjkAChaRu6M8yPxRWaB8SlRW00TXoyrPmoOu1hIpG6ykIWeZs+Gx2jBQs?=
 =?us-ascii?Q?16OQj2VtrSP8KHR/7rG8f9OZFH4G0kvbV60lzOHzQDtzD+g8ZHOHq3+h6E9H?=
 =?us-ascii?Q?0KwmovAOj940uyEbyduVGEeOUQs4VfxYf56x6mbx03Fv4tAmzVRhmQNO8Mm7?=
 =?us-ascii?Q?vFCCb2eGeK+AAQZxXbKlGodcIHWXDUIx6gXK35pdP8z2wMq6WL97k2XBvs9z?=
 =?us-ascii?Q?YMXKow3icmLXcN72x0Z9nVOln/58Cd9k9wacAJ6wf2kHYKc8R+pq3AYKq0Rh?=
 =?us-ascii?Q?863z6T5DKVIo/xNHLE2wa97aooGw6in0Tm2WqMfyWgCx+uK7LHpTk4/QfHUW?=
 =?us-ascii?Q?EzyczmaXNeEGAjGHFFCGPy3hUTgpVXGRibYak5zxK+mUv3Q4j2yZZIHThwSh?=
 =?us-ascii?Q?1PrN2QY1AtxIvYkVqNM2HvrHbTbSCxwhjxkEBZIn0EuI1RKWPLWX6sO3SJMj?=
 =?us-ascii?Q?AYm2lDHE/SfAOo3qCZqhdu8aSZX4e6QO+MF0F3OhoqOpX9HXAogN7bAm/M5+?=
 =?us-ascii?Q?t6M1jN7IQwNJb1++8PFS9xd6f0rLbWNOg2xNe0AkQc1dXLc6MlPnNI8vayQ9?=
 =?us-ascii?Q?MfzTPcIyE6LbowvuezfktYgaKOH2xznbrCMjyPnDOy2hILpYp86yXAKm8kb9?=
 =?us-ascii?Q?LinJknNdYeYMAR8ARSzmsn+QEuTYAePn/h6i/tpgV++XEKPnYRzDSmzyIfI6?=
 =?us-ascii?Q?vcD58ypKAnU9S/aRTKCL6qVcrlwL4QcR2T34sSo9oArjrhbKq9qjsOAW3wgd?=
 =?us-ascii?Q?iAnZzcx1FF4xEjjdQ+Cu4GPaLCtOhG0MPdQaAW8DhnmuppsB8taf8ry/FQx/?=
 =?us-ascii?Q?zE0c1+66vv8lpnJeqdaQwS3ZUzp0jlSwB4sY9Xs69r9chmrOBSQrHkPK6McG?=
 =?us-ascii?Q?xKuZ7urnDbaQ6g8qVtpBbGsxIdI+s/RTHwix3/580OgVeBKmICDvatQ24YDD?=
 =?us-ascii?Q?p9KT73ISMwCxAmgBnJiXul2O3h0aeLlDIpiHrydd8OtZDEggYPMBQk1laFCs?=
 =?us-ascii?Q?8VuauMlhjpBL8v9unThcd088q4QyLPsZgNtzxafAzlIluaAnIHhfpSzCXoEp?=
 =?us-ascii?Q?GbdoqXyRKFT1gBi1rJAdcVAJ/I37kPbVJsnhgdOTTLH5JAIK+PMigMKDKBxZ?=
 =?us-ascii?Q?rg+xt02ZYMTyoQDNx6EuPBoPq1nd0rL1NA3br6uuC51f?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 112261da-66f3-43ad-a952-08da5aa8000e
X-MS-Exchange-CrossTenant-AuthSource: DM4PR11MB6311.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Jun 2022 14:51:22.9406
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: ZDrdMD9b8H3ifEBZpzmyFDxnekLemGJaK83+WupMuDAT8UCN6fZPNS7xTVhR8zgdRJIbOAjI1QWmXVO5gWMHEg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR1101MB2165
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-4.8 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,
        SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham
        autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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>

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
>  fs/btrfs/zlib.c | 32 +++++++++++++-------------------
>  1 file changed, 13 insertions(+), 19 deletions(-)
> 
> diff --git a/fs/btrfs/zlib.c b/fs/btrfs/zlib.c
> index 770c4c6bbaef..b4f44662cda7 100644
> --- a/fs/btrfs/zlib.c
> +++ b/fs/btrfs/zlib.c
> @@ -97,7 +97,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
>  {
>  	struct workspace *workspace = list_entry(ws, struct workspace, list);
>  	int ret;
> -	char *data_in;
> +	char *data_in = NULL;
>  	char *cpage_out;
>  	int nr_pages = 0;
>  	struct page *in_page = NULL;
> @@ -126,7 +126,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
>  		ret = -ENOMEM;
>  		goto out;
>  	}
> -	cpage_out = kmap(out_page);
> +	cpage_out = page_address(out_page);
>  	pages[0] = out_page;
>  	nr_pages = 1;
>  
> @@ -148,26 +148,26 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
>  				int i;
>  
>  				for (i = 0; i < in_buf_pages; i++) {
> -					if (in_page) {
> -						kunmap(in_page);
> +					if (data_in) {
> +						kunmap_local(data_in);
>  						put_page(in_page);
>  					}
>  					in_page = find_get_page(mapping,
>  								start >> PAGE_SHIFT);
> -					data_in = kmap(in_page);
> +					data_in = kmap_local_page(in_page);
>  					memcpy(workspace->buf + i * PAGE_SIZE,
>  					       data_in, PAGE_SIZE);
>  					start += PAGE_SIZE;
>  				}
>  				workspace->strm.next_in = workspace->buf;
>  			} else {
> -				if (in_page) {
> -					kunmap(in_page);
> +				if (data_in) {
> +					kunmap_local(data_in);
>  					put_page(in_page);
>  				}
>  				in_page = find_get_page(mapping,
>  							start >> PAGE_SHIFT);
> -				data_in = kmap(in_page);
> +				data_in = kmap_local_page(in_page);
>  				start += PAGE_SIZE;
>  				workspace->strm.next_in = data_in;
>  			}
> @@ -196,9 +196,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
>  		 * the stream end if required
>  		 */
>  		if (workspace->strm.avail_out == 0) {
> -			kunmap(out_page);
>  			if (nr_pages == nr_dest_pages) {
> -				out_page = NULL;
>  				ret = -E2BIG;
>  				goto out;
>  			}
> @@ -207,7 +205,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
>  				ret = -ENOMEM;
>  				goto out;
>  			}
> -			cpage_out = kmap(out_page);
> +			cpage_out = page_address(out_page);
>  			pages[nr_pages] = out_page;
>  			nr_pages++;
>  			workspace->strm.avail_out = PAGE_SIZE;
> @@ -234,9 +232,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
>  			goto out;
>  		} else if (workspace->strm.avail_out == 0) {
>  			/* get another page for the stream end */
> -			kunmap(out_page);
>  			if (nr_pages == nr_dest_pages) {
> -				out_page = NULL;
>  				ret = -E2BIG;
>  				goto out;
>  			}
> @@ -245,7 +241,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
>  				ret = -ENOMEM;
>  				goto out;
>  			}
> -			cpage_out = kmap(out_page);
> +			cpage_out = page_address(out_page);
>  			pages[nr_pages] = out_page;
>  			nr_pages++;
>  			workspace->strm.avail_out = PAGE_SIZE;
> @@ -264,13 +260,11 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
>  	*total_in = workspace->strm.total_in;
>  out:
>  	*out_pages = nr_pages;
> -	if (out_page)
> -		kunmap(out_page);
> -
> -	if (in_page) {
> -		kunmap(in_page);
> +	if (data_in) {
> +		kunmap_local(data_in);
>  		put_page(in_page);
>  	}
> +
>  	return ret;
>  }
>  
> -- 
> 2.36.1
>