Re: [dpdk-dev] [RFC V1] examples/l3fwd-power: fix memory leak for rte_pci_device

[Thomas Monjalon <thomas@monjalon.net>]

16/09/2021 10:01, Huisong Li:
> 在 2021/9/8 15:20, Thomas Monjalon 写道:
> > 08/09/2021 04:01, Huisong Li:
> >> 在 2021/9/7 16:53, Thomas Monjalon 写道:
> >>> 07/09/2021 05:41, Huisong Li:
> >>>> Calling rte_eth_dev_close() will release resources of eth device and close
> >>>> it. But rte_pci_device struct isn't released when app exit, which will lead
> >>>> to memory leak.
> >>> That's a PMD issue.
> >>> When the last port of a PCI device is closed, the device should be freed.
> >> Why is this a PMD problem? I don't understand.
> > 
> > In the PMD close function, freeing of PCI device must be managed,
> > so the app doesn't have to bother.
> 
> I know what you mean. Currently, there are two ways to close PMD device 
> (rte_eth_dev_close() and rte_dev_remove()).
> 
> For rte_dev_remove(), eth device can be closed and rte_pci_device also 
> can be freed, so it can make app not care about that.
> 
> But dev_close() is only used to close eth device, and nothing about 
> rte_pci_device is involved in the framework layer
> 
> call stack of dev_close(). The rte_pci_device is allocated and 
> initialized when the rte_pci_bus scans "/sys/bus/pci/devices" directory.
> 
> Generally, the PMD of eth devices operates on the basis of eth devices, 
> and rarely on rte_pci_device.

No. The PMD is doing the relation between the PCI device and the ethdev port.

> And the rte_pci_device corresponding to the eth devices managed and 
> processed by rte_pci_bus.
> 
> So, PMD is closed only based on the port ID of the eth device, whilch 
> only shuts down eth devices, not frees rte_pci_device
> and remove it from rte_pci_bus.

Not really.
If there is no port using the PCI device, it should be released.

> >> As far as I know, most apps or examples in the DPDK project have only
> >> one port for a pci device.
> > The number of ports per PCI device is driver-specific.
> >
> >> When the port is closed, the rte_pci_device should be freed. But none of
> >> the apps seem to do this.
> > 
> > That's because from the app point of view, only ports should be managed.
> > The hardware device is managed by the PMD.
> > Only drivers (PMDs) have to do the relation between class ports
> > and hardware devices.
> 
> Yes. But the current app only closes the port to disable the PMD, and 
> the rte_pci_device cannot be freed.

Why not?

> Because rte_pci_device cannot be released in dev_close() of PMD, and is 
> managed by framework layer.

No

> Btw. Excluding rte_dev_probe() and rte_dev_remove(),  it seems that the 
> DPDK framework only automatically
> scans PCI devices, but does not automatically release PCI devices when 
> the process exits.

Indeed, because such freeing is the responsibility of the PMD.