linux-kernel - Re: [PATCH 02/12] pci/p2pdma: Don't initialise page refcount to one

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Message-ID: <20240910134745.GA577955@bhelgaas>
Date: Tue, 10 Sep 2024 08:47:45 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Alistair Popple <apopple@...dia.com>
Cc: dan.j.williams@...el.com, linux-mm@...ck.org, vishal.l.verma@...el.com,
	dave.jiang@...el.com, logang@...tatee.com, bhelgaas@...gle.com,
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	david@...morbit.com
Subject: Re: [PATCH 02/12] pci/p2pdma: Don't initialise page refcount to one

In subject:

  PCI/P2PDMA: ...

would match previous history.

On Tue, Sep 10, 2024 at 02:14:27PM +1000, Alistair Popple wrote:
> The reference counts for ZONE_DEVICE private pages should be
> initialised by the driver when the page is actually allocated by the
> driver allocator, not when they are first created. This is currently
> the case for MEMORY_DEVICE_PRIVATE and MEMORY_DEVICE_COHERENT pages
> but not MEMORY_DEVICE_PCI_P2PDMA pages so fix that up.
> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>
> ---
>  drivers/pci/p2pdma.c |  6 ++++++
>  mm/memremap.c        | 17 +++++++++++++----
>  mm/mm_init.c         | 22 ++++++++++++++++++----
>  3 files changed, 37 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 4f47a13..210b9f4 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -129,6 +129,12 @@ static int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj,
>  	}
>  
>  	/*
> +	 * Initialise the refcount for the freshly allocated page. As we have
> +	 * just allocated the page no one else should be using it.
> +	 */
> +	set_page_count(virt_to_page(kaddr), 1);

No doubt the subject line is true in some overall context, but it does
seem to say the opposite of what happens here.

Bjorn