linux-kernel - Re: [PATCH RFC 0/7] block: Introduce CBD (CXL Block Device)

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Message-ID: <66288ac38b770_a96f294c6@dwillia2-mobl3.amr.corp.intel.com.notmuch>
Date: Tue, 23 Apr 2024 21:29:55 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Dongsheng Yang <dongsheng.yang@...ystack.cn>, <dan.j.williams@...el.com>,
	<axboe@...nel.dk>
CC: <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-cxl@...r.kernel.org>, Dongsheng Yang <dongsheng.yang.linux@...il.com>
Subject: Re: [PATCH RFC 0/7] block: Introduce CBD (CXL Block Device)

Dongsheng Yang wrote:
> From: Dongsheng Yang <dongsheng.yang.linux@...il.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.