Re: [PATCH v7 20/21] PCI/P2PDMA: Introduce pci_mmap_p2pmem()

Logan Gunthorpe
2022-06-29T16:00:43Z

On 2022-06-29 00:48, Christoph Hellwig wrote:
> On Wed, Jun 15, 2022 at 10:12:32AM -0600, Logan Gunthorpe wrote:
>> A pseudo mount is used to allocate an inode for each PCI device. The
>> inode's address_space is used in the file doing the mmap so that all
>> VMAs are collected and can be unmapped if the PCI device is unbound.
>> After unmapping, the VMAs are iterated through and their pages are
>> put so the device can continue to be unbound. An active flag is used
>> to signal to VMAs not to allocate any further P2P memory once the
>> removal process starts. The flag is synchronized with concurrent
>> access with an RCU lock.
>
> Can't we come up with a way of doing this without all the pseudo-fs
> garbagage? I really hate all the overhead for that in the next
> nvme patch as well.

I assume you still want to be able to unmap the VMAs on unbind and not
just hang?

I'll see if I can come up with something to do the a similar thing using
vm_private data or some such.

I was not a fan of the extra code for this either, but I was given to
understand that it was the standard way to collect and cleanup VMAs.

Thanks for the reviews,

Logan