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

Christoph Hellwig
2022-07-05T16:40:42Z

On Tue, Jul 05, 2022 at 01:29:59PM -0300, Jason Gunthorpe wrote:
> > Making the entire area given by the device to the p2p allocator available
> > to user space seems sensible to me. That is what the current series does,
> > and what a sysfs interface would do as well.
>
> That makes openning the mmap exclusive with the in-kernel allocator -
> so it means opening the mmap fails if something else is using a P2P
> page and once the mmap is open all kernel side P2P allocations will
> fail?

No. Just as in the current patchset you can mmap the file and will get
len / PAGE_SIZE pages from the per-device p2pdma pool, or the mmap will
fail if none are available. A kernel consumer (or multiple) can use
other pages in the pool at the same time.