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@xxxxxxxxx> > >> > >> 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. > > That is to say, in my view, FAMfs and cbd do not conflict at all; they > meet different scenario requirements. cbd simply uses shared memory to > transmit data, shared memory plays the role of a data transmission > channel, while in FAMfs, shared memory serves as a data store role. If shared memory is just a communication transport then a block-device abstraction does not seem a proper fit. From the above description this sounds similar to what CONFIG_NTB_TRANSPORT offers which is a way for two hosts to communicate over a shared memory channel. So, I am not really looking for an analysis of famfs vs CBD I am looking for CBD to clarify why Linux should consider it, and why the architecture is fit for purpose.
