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Thunderbird/95.0 Subject: Re: [6.2 regression][bisected]discard storm on idle since v6.1-rc8-59-g63a7cb130718 discard=async To: Sergei Trofimovich , linux-btrfs@vger.kernel.org Cc: David Sterba , Boris Burkov , Chris Mason , Josef Bacik References: From: Anand Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SG2PR02CA0077.apcprd02.prod.outlook.com (2603:1096:4:90::17) To PH0PR10MB5706.namprd10.prod.outlook.com (2603:10b6:510:148::10) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH0PR10MB5706:EE_|PH7PR10MB6249:EE_ X-MS-Office365-Filtering-Correlation-Id: 5aeeaa7f-274c-45fb-5c93-08db1afe4339 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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5aeeaa7f-274c-45fb-5c93-08db1afe4339 X-MS-Exchange-CrossTenant-AuthSource: PH0PR10MB5706.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Mar 2023 09:12:35.7873 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: QzWWrZTa3lp+ZbJdlf3YL8w15iU7MVcUo42INlKgmPo5rj1E5XTa1tthpfwEVGRIYXTFKYmnY9a4wWsGHDVKlw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR10MB6249 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-03-02_04,2023-03-02_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 bulkscore=0 adultscore=0 mlxlogscore=999 suspectscore=0 phishscore=0 spamscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2303020079 X-Proofpoint-GUID: XeWSJROHNfinrxRk2T6ltx-PPeXYP-sB X-Proofpoint-ORIG-GUID: XeWSJROHNfinrxRk2T6ltx-PPeXYP-sB Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 3/2/23 03:30, Sergei Trofimovich wrote: > Hi btrfs maintainers! > > Tl;DR: > > After 63a7cb13071842 "btrfs: auto enable discard=async when possible" I > see constant DISCARD storm towards my NVME device be it idle or not. > > No storm: v6.1 and older > Has storm: v6.2 and newer > > More words: > > After upgrade from 6.1 to 6.2 I noticed that Disk led on my desktop > started flashing incessantly regardless of present or absent workload. > > I think I confirmed the storm with `perf`: led flashes align with output > of: > > # perf ftrace -a -T 'nvme_setup*' | cat > > kworker/6:1H-298 [006] 2569.645201: nvme_setup_cmd <-nvme_queue_rq > kworker/6:1H-298 [006] 2569.645205: nvme_setup_discard <-nvme_setup_cmd > kworker/6:1H-298 [006] 2569.749198: nvme_setup_cmd <-nvme_queue_rq > kworker/6:1H-298 [006] 2569.749202: nvme_setup_discard <-nvme_setup_cmd > kworker/6:1H-298 [006] 2569.853204: nvme_setup_cmd <-nvme_queue_rq > kworker/6:1H-298 [006] 2569.853209: nvme_setup_discard <-nvme_setup_cmd > kworker/6:1H-298 [006] 2569.958198: nvme_setup_cmd <-nvme_queue_rq > kworker/6:1H-298 [006] 2569.958202: nvme_setup_discard <-nvme_setup_cmd > > `iotop` shows no read/write IO at all (expected). > > I was able to bisect it down to this commit: > > $ git bisect good > 63a7cb13071842966c1ce931edacbc23573aada5 is the first bad commit > commit 63a7cb13071842966c1ce931edacbc23573aada5 > Author: David Sterba > Date: Tue Jul 26 20:54:10 2022 +0200 > > btrfs: auto enable discard=async when possible > > There's a request to automatically enable async discard for capable > devices. We can do that, the async mode is designed to wait for larger > freed extents and is not intrusive, with limits to iops, kbps or latency. > > The status and tunables will be exported in /sys/fs/btrfs/FSID/discard . > > The automatic selection is done if there's at least one discard capable > device in the filesystem (not capable devices are skipped). Mounting > with any other discard option will honor that option, notably mounting > with nodiscard will keep it disabled. > > Link: https://lore.kernel.org/linux-btrfs/CAEg-Je_b1YtdsCR0zS5XZ_SbvJgN70ezwvRwLiCZgDGLbeMB=w@mail.gmail.com/ > Reviewed-by: Boris Burkov > Signed-off-by: David Sterba > > fs/btrfs/ctree.h | 1 + > fs/btrfs/disk-io.c | 14 ++++++++++++++ > fs/btrfs/super.c | 2 ++ > fs/btrfs/volumes.c | 3 +++ > fs/btrfs/volumes.h | 2 ++ > 5 files changed, 22 insertions(+) > > Is this storm a known issue? I did not dig too much into the patch. But > glancing at it this bit looks slightly off: > > + if (bdev_max_discard_sectors(bdev)) > + fs_devices->discardable = true; > > Is it expected that there is no `= false` assignment? > > This is the list of `btrfs` filesystems I have: > > $ cat /proc/mounts | fgrep btrfs > /dev/nvme0n1p3 / btrfs rw,noatime,compress=zstd:3,ssd,space_cache,subvolid=848,subvol=/nixos 0 0 > /dev/sda3 /mnt/archive btrfs rw,noatime,compress=zstd:3,space_cache,subvolid=5,subvol=/ 0 0 > # skipped bind mounts > > The device is: > > $ lspci | fgrep -i Solid > 01:00.0 Non-Volatile memory controller: ADATA Technology Co., Ltd. XPG SX8200 Pro PCIe Gen3x4 M.2 2280 Solid State Drive (rev 03) It is a SSD device with NVME interface, that needs regular discard. Why not try tune io intensity using /sys/fs/btrfs//discard options? Maybe not all discardable sectors are not issued at once. It is a good idea to try with a fresh mkfs (which runs discard at mkfs) to see if discard is being issued even if there are no fs activities. Thanks, Anand