Re: [PATCH 02/13] pci/p2pdma: Don't initialise page refcount to one

Bjorn Helgaas
2024-06-29T21:28:53Z

On Thu, Jun 27, 2024 at 10:54:17AM +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.

If you tag the subject line with PCI, please run "git log --oneline
drivers/pci/p2pdma.c" and make yours look like previous ones
("PCI/P2PDMA").

Also recast it to say something semantically useful about what it
*does*, not what it *doesn't* do. Maybe something about initializing
the refcount where the page is allocated? Especially since the only
p2pdma.c change here is to "set_page_count(..., 1)", which looks like
exactly the opposite of "don't initialize refcount to one".

> Signed-off-by: Alistair Popple <apopple@nvidia.com>
> ---
> drivers/pci/p2pdma.c | 2 ++
> mm/memremap.c | 8 ++++----
> mm/mm_init.c | 4 +++-
> 3 files changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index 4f47a13..1e9ea32 100644
> --- a/drivers/pci/p2pdma.c
> +++ b/drivers/pci/p2pdma.c
> @@ -128,6 +128,8 @@ static int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj,
> goto out;
> }
>
> + set_page_count(virt_to_page(kaddr), 1);
> +
> /*
> * vm_insert_page() can sleep, so a reference is taken to mapping
> * such that rcu_read_unlock() can be done before inserting the
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 40d4547..caccbd8 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -488,15 +488,15 @@ void free_zone_device_folio(struct folio *folio)
> folio->mapping = NULL;
> folio->page.pgmap->ops->page_free(folio_page(folio, 0));
>
> - if (folio->page.pgmap->type != MEMORY_DEVICE_PRIVATE &&
> - folio->page.pgmap->type != MEMORY_DEVICE_COHERENT)
> + if (folio->page.pgmap->type == MEMORY_DEVICE_PRIVATE ||
> + folio->page.pgmap->type == MEMORY_DEVICE_COHERENT)
> + put_dev_pagemap(folio->page.pgmap);
> + else if (folio->page.pgmap->type != MEMORY_DEVICE_PCI_P2PDMA)
> /*
> * Reset the refcount to 1 to prepare for handing out the page
> * again.
> */
> folio_set_count(folio, 1);
> - else
> - put_dev_pagemap(folio->page.pgmap);
> }
>
> void zone_device_page_init(struct page *page)
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 3ec0493..b7e1599 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -6,6 +6,7 @@
> * Author Mel Gorman <mel@csn.ul.ie>
> *
> */
> +#include "linux/memremap.h"
> #include <linux/kernel.h>
> #include <linux/init.h>
> #include <linux/kobject.h>
> @@ -1014,7 +1015,8 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
> * which will set the page count to 1 when allocating the page.
> */
> if (pgmap->type == MEMORY_DEVICE_PRIVATE ||
> - pgmap->type == MEMORY_DEVICE_COHERENT)
> + pgmap->type == MEMORY_DEVICE_COHERENT ||
> + pgmap->type == MEMORY_DEVICE_PCI_P2PDMA)
> set_page_count(page, 0);
> }
>
> --
> git-series 0.9.1