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Tue, 3 Feb 2026 20:38:21 +0000 Date: Tue, 3 Feb 2026 14:41:42 -0600 From: Ira Weiny To: "Michael S. Tsirkin" , Li Chen CC: Pankaj Gupta , Dan Williams , Vishal Verma , "Dave Jiang" , Ira Weiny , Cornelia Huck , Yuval Shaia , , , Subject: Re: [PATCH v2] nvdimm: virtio_pmem: serialize flush requests Message-ID: <69825d866edd7_44a2210014@iweiny-mobl.notmuch> References: <20260203021353.121091-1-me@linux.beauty> <20260203052616-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260203052616-mutt-send-email-mst@kernel.org> X-ClientProxiedBy: BYAPR02CA0007.namprd02.prod.outlook.com (2603:10b6:a02:ee::20) To PH3PPF9E162731D.namprd11.prod.outlook.com (2603:10b6:518:1::d3c) Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH3PPF9E162731D:EE_|SJ2PR11MB7456:EE_ X-MS-Office365-Filtering-Correlation-Id: 04c43345-d79a-481e-ea27-08de63642be1 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016|7053199007; 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Tsirkin wrote: > On Tue, Feb 03, 2026 at 10:13:51AM +0800, Li Chen wrote: > > Under heavy concurrent flush traffic, virtio-pmem can overflow its request > > virtqueue (req_vq): virtqueue_add_sgs() starts returning -ENOSPC and the > > driver logs "no free slots in the virtqueue". Shortly after that the > > device enters VIRTIO_CONFIG_S_NEEDS_RESET and flush requests fail with > > "virtio pmem device needs a reset". > > > > Serialize virtio_pmem_flush() with a per-device mutex so only one flush > > request is in-flight at a time. This prevents req_vq descriptor overflow > > under high concurrency. > > > > Reproducer (guest with virtio-pmem): > > - mkfs.ext4 -F /dev/pmem0 > > - mount -t ext4 -o dax,noatime /dev/pmem0 /mnt/bench > > - fio: ioengine=io_uring rw=randwrite bs=4k iodepth=64 numjobs=64 > > direct=1 fsync=1 runtime=30s time_based=1 > > - dmesg: "no free slots in the virtqueue" > > "virtio pmem device needs a reset" > > > > Fixes: 6e84200c0a29 ("virtio-pmem: Add virtio pmem driver") > > Signed-off-by: Li Chen > > > Thanks! > And the commit message looks good now and includes the > reproducer. > > Acked-by: Michael S. Tsirkin > > Ira are you picking this up? > Yes queued for 7.0 Ira [snip]