linux-kernel - Re: [PATCH] mm: Cleanup __put_devmap_managed_page() vs ->page

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Date:   Wed, 13 Nov 2019 20:24:41 -0500
From:   Jerome Glisse <jglisse@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     jhubbard@...dia.com, Jan Kara <jack@...e.cz>,
        Christoph Hellwig <hch@....de>,
        Ira Weiny <ira.weiny@...el.com>, linux-nvdimm@...ts.01.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: Cleanup __put_devmap_managed_page() vs ->page_free()

On Wed, Nov 13, 2019 at 04:07:22PM -0800, Dan Williams wrote:
> After the removal of the device-public infrastructure there are only 2
> ->page_free() call backs in the kernel. One of those is a device-private
> callback in the nouveau driver, the other is a generic wakeup needed in
> the DAX case. In the hopes that all ->page_free() callbacks can be
> migrated to common core kernel functionality, move the device-private
> specific actions in __put_devmap_managed_page() under the
> is_device_private_page() conditional, including the ->page_free()
> callback. For the other page types just open-code the generic wakeup.
> 
> Yes, the wakeup is only needed in the MEMORY_DEVICE_FSDAX case, but it
> does no harm in the MEMORY_DEVICE_DEVDAX and MEMORY_DEVICE_PCI_P2PDMA
> case.
> 
> Cc: Jan Kara <jack@...e.cz>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Cc: Jérôme Glisse <jglisse@...hat.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>

All looks good to me.

Reviewed-by: Jérôme Glisse <jglisse@...hat.com>


> ---
> Hi John,
> 
> This applies on top of today's linux-next and passes my nvdimm unit
> tests. That testing noticed that devmap_managed_enable_get() needed a
> small fixup as well.
> 
>  drivers/nvdimm/pmem.c |    6 ------
>  mm/memremap.c         |   22 ++++++++++++----------
>  2 files changed, 12 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index f9f76f6ba07b..21db1ce8c0ae 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -338,13 +338,7 @@ static void pmem_release_disk(void *__pmem)
>  	put_disk(pmem->disk);
>  }
>  
> -static void pmem_pagemap_page_free(struct page *page)
> -{
> -	wake_up_var(&page->_refcount);
> -}
> -
>  static const struct dev_pagemap_ops fsdax_pagemap_ops = {
> -	.page_free		= pmem_pagemap_page_free,
>  	.kill			= pmem_pagemap_kill,
>  	.cleanup		= pmem_pagemap_cleanup,
>  };
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 022e78e68ea0..6e6f3d6fdb73 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -27,7 +27,8 @@ static void devmap_managed_enable_put(void)
>  
>  static int devmap_managed_enable_get(struct dev_pagemap *pgmap)
>  {
> -	if (!pgmap->ops || !pgmap->ops->page_free) {
> +	if (!pgmap->ops || (pgmap->type == MEMORY_DEVICE_PRIVATE
> +				&& !pgmap->ops->page_free)) {
>  		WARN(1, "Missing page_free method\n");
>  		return -EINVAL;
>  	}
> @@ -449,12 +450,6 @@ void __put_devmap_managed_page(struct page *page)
>  	 * holds a reference on the page.
>  	 */
>  	if (count == 1) {
> -		/* Clear Active bit in case of parallel mark_page_accessed */
> -		__ClearPageActive(page);
> -		__ClearPageWaiters(page);
> -
> -		mem_cgroup_uncharge(page);
> -
>  		/*
>  		 * When a device_private page is freed, the page->mapping field
>  		 * may still contain a (stale) mapping value. For example, the
> @@ -476,10 +471,17 @@ void __put_devmap_managed_page(struct page *page)
>  		 * handled differently or not done at all, so there is no need
>  		 * to clear page->mapping.
>  		 */
> -		if (is_device_private_page(page))
> -			page->mapping = NULL;
> +		if (is_device_private_page(page)) {
> +			/* Clear Active bit in case of parallel mark_page_accessed */
> +			__ClearPageActive(page);
> +			__ClearPageWaiters(page);
>  
> -		page->pgmap->ops->page_free(page);
> +			mem_cgroup_uncharge(page);
> +
> +			page->mapping = NULL;
> +			page->pgmap->ops->page_free(page);
> +		} else
> +			wake_up_var(&page->_refcount);
>  	} else if (!count)
>  		__put_page(page);
>  }
>