linux-kernel - Re: [PATCH v6 02/13] PCI/P2PDMA: Add sysfs group to display p2pmem stats

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Date:   Fri, 21 Sep 2018 08:07:05 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-block@...r.kernel.org,
        Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Christian König <christian.koenig@....com>,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v6 02/13] PCI/P2PDMA: Add sysfs group to display p2pmem
 stats

On Wed, Sep 12, 2018 at 06:11:45PM -0600, Logan Gunthorpe wrote:
> Add a sysfs group to display statistics about P2P memory that is
> registered in each PCI device.
> 
> Attributes in the group display the total amount of P2P memory, the
> amount available and whether it is published or not.
> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

> +What:		/sys/bus/pci/devices/.../p2pmem/available
> +Date:		November 2017
> +Contact:	Logan Gunthorpe <logang@...tatee.com>
> +Description:
> +		If the device has any Peer-to-Peer memory registered, this
> +	        file contains the amount of memory that has not been
> +		allocated (in decimal).
> +
> +What:		/sys/bus/pci/devices/.../p2pmem/size
> +Date:		November 2017
> +Contact:	Logan Gunthorpe <logang@...tatee.com>
> +Description:
> +		If the device has any Peer-to-Peer memory registered, this
> +	        file contains the total amount of memory that the device
> +		provides (in decimal).

Maybe reorder this so the "size" (total amount) is documented before
"available" (some subset of "size")?

> +
> +What:		/sys/bus/pci/devices/.../p2pmem/published
> +Date:		November 2017
> +Contact:	Logan Gunthorpe <logang@...tatee.com>
> +Description:
> +		If the device has any Peer-to-Peer memory registered, this
> +	        file contains a '1' if the memory has been published for
> +		use inside the kernel or a '0' if it is only intended
> +		for use within the driver that published it.

It doesn't read quite right to talk about "use within the driver that
*published* it".  Is it really published in that case?  That sounds more
like "private".  I expected something like the following (but I don't claim
to understand the whole use model here):

  ... this file contains a '1' if the memory has been published for use
  outside the driver that owns the device.