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From: Dongsheng Yang <dongsheng.yang@easystack.cn>
To: Gregory Price <gregory.price@memverge.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
	axboe@kernel.dk, John Groves <John@groves.net>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-cxl@vger.kernel.org,
	Dongsheng Yang <dongsheng.yang.linux@gmail.com>
Subject: Re: [PATCH RFC 0/7] block: Introduce CBD (CXL Block Device)
Date: Fri, 26 Apr 2024 09:25:53 +0800	[thread overview]
Message-ID: <bbf692ec-2109-baf2-aaae-7859a8315025@easystack.cn> (raw)
In-Reply-To: <ZikhwAAIGFG0UU23@memverge.com>



在 2024/4/24 星期三 下午 11:14, Gregory Price 写道:
> On Wed, Apr 24, 2024 at 02:33:28PM +0800, Dongsheng Yang wrote:
>>
>>
>> 在 2024/4/24 星期三 下午 12:29, Dan Williams 写道:
>>> Dongsheng Yang wrote:
>>>> From: Dongsheng Yang <dongsheng.yang.linux@gmail.com>
>>>>
>>>> Hi all,
>>>> 	This patchset introduce cbd (CXL block device). It's based on linux 6.8, and available at:
>>>> 	https://github.com/DataTravelGuide/linux
>>>>
>>> [..]
>>>> (4) dax is not supported yet:
>>>> 	same with famfs, dax device is not supported here, because dax device does not support
>>>> dev_dax_iomap so far. Once dev_dax_iomap is supported, CBD can easily support DAX mode.
>>>
>>> I am glad that famfs is mentioned here, it demonstrates you know about
>>> it. However, unfortunately this cover letter does not offer any analysis
>>> of *why* the Linux project should consider this additional approach to
>>> the inter-host shared-memory enabling problem.
>>>
>>> To be clear I am neutral at best on some of the initiatives around CXL
>>> memory sharing vs pooling, but famfs at least jettisons block-devices
>>> and gets closer to a purpose-built memory semantic.
>>>
>>> So my primary question is why would Linux need both famfs and cbd? I am
>>> sure famfs would love feedback and help vs developing competing efforts.
>>
>> Hi,
>> 	Thanks for your reply, IIUC about FAMfs, the data in famfs is stored in
>> shared memory, and related nodes can share the data inside this file system;
>> whereas cbd does not store data in shared memory, it uses shared memory as a
>> channel for data transmission, and the actual data is stored in the backend
>> block device of remote nodes. In cbd, shared memory works more like network
>> to connect different hosts.
>>
> 
> Couldn't you basically just allocate a file for use as a uni-directional
> buffer on top of FAMFS and achieve the same thing without the need for
> additional kernel support? Similar in a sense to allocating a file on
> network storage and pinging the remote host when it's ready (except now
> it's fast!)

I'm not entirely sure I follow your suggestion. I guess it means that 
cbd would no longer directly manage the pmem device, but allocate files 
on famfs to transfer data. I didn't do it this way because I considered 
at least a few points: one of them is, cbd_transport actually requires a 
DAX device to access shared memory, and cbd has very simple requirements 
for space management, so there's no need to rely on a file system layer, 
which would increase architectural complexity.

However, we still need cbd_blkdev to provide a block device, so it 
doesn't achieve "achieve the same without the need for additional kernel 
support".

Could you please provide more specific details about your suggestion?
> 
> (The point here is not "FAMFS is better" or "CBD is better", simply
> trying to identify the function that will ultimately dictate the form).

Thank you for your clarification. totally aggree with it, discussions 
always make the issues clearer.

Thanx
> 
> ~Gregory
> 

  reply	other threads:[~2024-04-26  1:26 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-22  7:15 [PATCH RFC 0/7] block: Introduce CBD (CXL Block Device) Dongsheng Yang
2024-04-22  7:16 ` [PATCH 1/7] block: Init for CBD(CXL " Dongsheng Yang
2024-04-22 18:39   ` Randy Dunlap
2024-04-22 22:41     ` Dongsheng Yang
2024-04-24  3:58   ` Chaitanya Kulkarni
2024-04-24  8:36     ` Dongsheng Yang
2024-04-22  7:16 ` [PATCH 2/7] cbd: introduce cbd_transport Dongsheng Yang
2024-04-24  4:08   ` Chaitanya Kulkarni
2024-04-24  8:43     ` Dongsheng Yang
2024-04-22  7:16 ` [PATCH 3/7] cbd: introduce cbd_channel Dongsheng Yang
2024-04-22  7:16 ` [PATCH 4/7] cbd: introduce cbd_host Dongsheng Yang
2024-04-25  5:51   ` [EXTERNAL] " Bharat Bhushan
2024-04-22  7:16 ` [PATCH 5/7] cbd: introuce cbd_backend Dongsheng Yang
2024-04-24  5:03   ` Chaitanya Kulkarni
2024-04-24  8:36     ` Dongsheng Yang
2024-04-25  5:46   ` [EXTERNAL] " Bharat Bhushan
2024-04-22  7:16 ` [PATCH 7/7] cbd: add related sysfs files in transport register Dongsheng Yang
2024-04-25  5:24   ` [EXTERNAL] " Bharat Bhushan
2024-04-22 22:42 ` [PATCH 6/7] cbd: introduce cbd_blkdev Dongsheng Yang
2024-04-23  7:27   ` Dongsheng Yang
2024-04-24  4:29 ` [PATCH RFC 0/7] block: Introduce CBD (CXL Block Device) Dan Williams
2024-04-24  6:33   ` Dongsheng Yang
2024-04-24 15:14     ` Gregory Price
2024-04-26  1:25       ` Dongsheng Yang [this message]
2024-04-26 13:48         ` Gregory Price
2024-04-26 14:53           ` Dongsheng Yang
2024-04-26 16:14             ` Gregory Price
2024-04-28  5:47               ` Dongsheng Yang
2024-04-28 16:44                 ` Gregory Price
2024-04-28 16:55                 ` John Groves
2024-05-03  9:52                   ` Jonathan Cameron
2024-05-08 11:39                     ` Dongsheng Yang
2024-05-08 12:11                       ` Jonathan Cameron
2024-05-08 13:03                         ` Dongsheng Yang
2024-05-08 15:44                           ` Jonathan Cameron
2024-05-09 11:24                             ` Dongsheng Yang
2024-05-09 12:21                               ` Jonathan Cameron
2024-05-09 13:03                                 ` Dongsheng Yang
2024-05-21 18:41                                   ` Dan Williams
2024-05-22  6:17                                     ` Dongsheng Yang
2024-05-29 15:25                                       ` Gregory Price
2024-05-30  6:59                                         ` Dongsheng Yang
2024-05-30 13:38                                           ` Jonathan Cameron
2024-06-01  3:22                                             ` Dan Williams
2024-06-03 12:48                                               ` Jonathan Cameron
2024-06-03 17:28                                                 ` James Morse
2024-06-04 14:26                                                   ` Jonathan Cameron
2024-05-31 14:23                                           ` Gregory Price
2024-06-03  1:33                                             ` Dongsheng Yang
2024-04-30  0:34                 ` Dan Williams
2024-04-24 18:08     ` Dan Williams
     [not found]       ` <539c1323-68f9-d753-a102-692b69049c20@easystack.cn>
2024-04-30  0:10         ` Dan Williams

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