linux-kernel - Re: [PATCH V2 3/4] mm: add a function to differentiate the pages is from DAX device memory

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Date:   Tue, 7 Aug 2018 11:13:57 +0200
From:   Jan Kara <jack@...e.cz>
To:     Zhang Yi <yi.z.zhang@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, pbonzini@...hat.com,
        dan.j.williams@...el.com, jack@...e.cz, hch@....de,
        yu.c.zhang@...el.com, linux-mm@...ck.org, rkrcmar@...hat.com,
        yi.z.zhang@...el.com
Subject: Re: [PATCH V2 3/4] mm: add a function to differentiate the pages is
 from DAX device memory

On Wed 11-07-18 01:03:51, Zhang Yi wrote:
> DAX driver hotplug the device memory and move it to memory zone, these
> pages will be marked reserved flag, however, some other kernel componet
> will misconceive these pages are reserved mmio (ex: we map these dev_dax
> or fs_dax pages to kvm for DIMM/NVDIMM backend). Together with the type
> MEMORY_DEVICE_FS_DAX, we can use is_dax_page() to differentiate the pages
> is DAX device memory or not.
> 
> Signed-off-by: Zhang Yi <yi.z.zhang@...ux.intel.com>
> Signed-off-by: Zhang Yu <yu.c.zhang@...ux.intel.com>

The patch looks OK to me but I don't really feel too confident about this
part of the kernel... But feel free to add my:

Acked-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  include/linux/mm.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 6e19265..9f0f690 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -856,6 +856,13 @@ static inline bool is_device_public_page(const struct page *page)
>  		page->pgmap->type == MEMORY_DEVICE_PUBLIC;
>  }
>  
> +static inline bool is_dax_page(const struct page *page)
> +{
> +	return is_zone_device_page(page) &&
> +		(page->pgmap->type == MEMORY_DEVICE_FS_DAX ||
> +		page->pgmap->type == MEMORY_DEVICE_DEV_DAX);
> +}
> +
>  #else /* CONFIG_DEV_PAGEMAP_OPS */
>  static inline void dev_pagemap_get_ops(void)
>  {
> @@ -879,6 +886,11 @@ static inline bool is_device_public_page(const struct page *page)
>  {
>  	return false;
>  }
> +
> +static inline bool is_dax_page(const struct page *page)
> +{
> +	return false;
> +}
>  #endif /* CONFIG_DEV_PAGEMAP_OPS */
>  
>  static inline void get_page(struct page *page)
> -- 
> 2.7.4
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR