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Date:   Wed, 29 Jun 2022 10:00:09 -0600
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To:     Christoph Hellwig <hch@lst.de>
Cc:     linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
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        Xiong Jianxin <jianxin.xiong@intel.com>,
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        Chaitanya Kulkarni <ckulkarnilinux@gmail.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Bjorn Helgaas <bhelgaas@google.com>
References: <20220615161233.17527-1-logang@deltatee.com>
 <20220615161233.17527-21-logang@deltatee.com> <20220629064854.GD17576@lst.de>
From:   Logan Gunthorpe <logang@deltatee.com>
In-Reply-To: <20220629064854.GD17576@lst.de>
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Subject: Re: [PATCH v7 20/21] PCI/P2PDMA: Introduce pci_mmap_p2pmem()
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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