linux-kernel - Re: [PATCH V2 2/4] mm: introduce memory type MEMORY_DEVICE_DEV

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Date:   Wed, 8 Aug 2018 17:22:42 +0800
From:   "Zhang,Yi" <yi.z.zhang@...ux.intel.com>
To:     Jan Kara <jack@...e.cz>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, pbonzini@...hat.com,
        dan.j.williams@...el.com, hch@....de, yu.c.zhang@...el.com,
        linux-mm@...ck.org, rkrcmar@...hat.com, yi.z.zhang@...el.com
Subject: Re: [PATCH V2 2/4] mm: introduce memory type MEMORY_DEVICE_DEV_DAX



On 2018年08月07日 17:11, Jan Kara wrote:
> On Wed 11-07-18 01:01:59, Zhang Yi wrote:
>> Currently, NVDIMM pages will be marked 'PageReserved'. However, unlike
>> other reserved PFNs, pages on NVDIMM shall still behave like normal ones
>> in many cases, i.e. when used as backend memory of KVM guest. This patch
>> introduces a new memory type, MEMORY_DEVICE_DEV_DAX. And set this flag
>> while dax driver hotplug the device memory.
>>
>> Signed-off-by: Zhang Yi <yi.z.zhang@...ux.intel.com>
>> Signed-off-by: Zhang Yu <yu.c.zhang@...ux.intel.com>
>> ---
>>  drivers/dax/pmem.c       | 1 +
>>  include/linux/memremap.h | 9 +++++++++
>>  2 files changed, 10 insertions(+)
>>
>> diff --git a/drivers/dax/pmem.c b/drivers/dax/pmem.c
>> index fd49b24..fb3f363 100644
>> --- a/drivers/dax/pmem.c
>> +++ b/drivers/dax/pmem.c
>> @@ -111,6 +111,7 @@ static int dax_pmem_probe(struct device *dev)
>>  		return rc;
>>  
>>  	dax_pmem->pgmap.ref = &dax_pmem->ref;
>> +	dax_pmem->pgmap.type = MEMORY_DEVICE_DEV_DAX;
>>  	addr = devm_memremap_pages(dev, &dax_pmem->pgmap);
>>  	if (IS_ERR(addr))
>>  		return PTR_ERR(addr);
>> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
>> index 5ebfff6..a36bce8 100644
>> --- a/include/linux/memremap.h
>> +++ b/include/linux/memremap.h
>> @@ -53,11 +53,20 @@ struct vmem_altmap {
>>   * wakeup event whenever a page is unpinned and becomes idle. This
>>   * wakeup is used to coordinate physical address space management (ex:
>>   * fs truncate/hole punch) vs pinned pages (ex: device dma).
>> + *
>> + * MEMORY_DEVICE_DEV_DAX:
>> + * 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 differentiate the pages on NVDIMM with the
>> + * normal reserved pages.
> So I believe the description should be in terms of what kind of memory is
> the MEMORY_DEVICE_DEV_DAX type, not how users use this type. See comments
> for other memory types...
>
> 								Honza
Yes, agree, thanks for your kindly review. Jan.
>
>>   */
>>  enum memory_type {
>>  	MEMORY_DEVICE_PRIVATE = 1,
>>  	MEMORY_DEVICE_PUBLIC,
>>  	MEMORY_DEVICE_FS_DAX,
>> +	MEMORY_DEVICE_DEV_DAX,
>>  };
>>  
>>  /*
>> -- 
>> 2.7.4
>>