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

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Date:   Tue, 14 Aug 2018 01:41:40 +0800
From:   "Zhang,Yi" <yi.z.zhang@...ux.intel.com>
To:     Pankaj Gupta <pagupta@...hat.com>,
        Jérôme Glisse <jglisse@...hat.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



On 2018年08月09日 17:23, Pankaj Gupta 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>
>> ---
>>  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
Yes, it is, thanks for your remind, Pankaj.
Adding Jerome for Dan's questions on V1:
[Dan]:

Jerome, might there be any use case to pass MEMORY_DEVICE_PUBLIC
memory to a guest vm?

>
>> +
>>  #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
>>
>>