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Date:   Tue, 5 Jul 2022 18:40:19 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Jason Gunthorpe <jgg@ziepe.ca>
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Subject: Re: [PATCH v7 20/21] PCI/P2PDMA: Introduce pci_mmap_p2pmem()
Message-ID: <20220705164019.GB14215@lst.de>
References: <20220615161233.17527-1-logang@deltatee.com> <20220615161233.17527-21-logang@deltatee.com> <20220629064854.GD17576@lst.de> <99242789-66a6-bbd2-b56a-e47891f4522e@deltatee.com> <20220629175906.GU23621@ziepe.ca> <20220705075108.GB17451@lst.de> <20220705135102.GE23621@ziepe.ca> <20220705161240.GB13721@lst.de> <20220705162959.GH23621@ziepe.ca>
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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.