linux-kernel - Re: [PATCH V3 3/4] mm: add a function to differentiate the pages is from DAX device memory

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Message-ID: <872818364.892078.1533806608252.JavaMail.zimbra@redhat.com>
Date:   Thu, 9 Aug 2018 05:23:28 -0400 (EDT)
From:   Pankaj Gupta <pagupta@...hat.com>
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 <dan.j.williams@...el.com>, jack@...e.cz,
        hch@....de, yu c zhang <yu.c.zhang@...el.com>, linux-mm@...ck.org,
        rkrcmar@...hat.com, yi z zhang <yi.z.zhang@...el.com>
Subject: Re: [PATCH V3 3/4] mm: add a function to differentiate the pages is
 from DAX device memory


> 
> 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>
> ---
>  include/linux/mm.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 68a5121..de5cbc3 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -889,6 +889,13 @@ 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);
> +}

I think question from Dan for KVM VM with 'MEMORY_DEVICE_PUBLIC' still holds?
I am also interested to know if there is any use-case.

Thanks,
Pankaj

> +
>  #else /* CONFIG_DEV_PAGEMAP_OPS */
>  static inline void dev_pagemap_get_ops(void)
>  {
> @@ -912,6 +919,11 @@ 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
> 
>