Re: Deep flush support for CXL pmem?

[Gregory Price <gourry@gourry.net>]

On Fri, Oct 17, 2025 at 02:11:16PM +0800, Huang, Ying wrote:
> Hi, All,
> 
> When reading the documentation of PMDK (https://github.com/pmem/pmdk), I
> found that deep flush is used for data loss recovery in addition to GPF.
> With that, we can identify that a file isn't affected by the GPF failure
> because it wasn't opened during the GPF failure.
> 
> However, IIUC, the Linux kernel doesn't support deep flush (via
> nvdimm_flush()) for CXL pmem at least for now.  For NVDIMM, we have WPQ,
> but it appears that we don't have that for CXL.  Is deep flush for CXL
> defined in some spec?
>

Should note that this is relevant not just for pmem, but also for shared
memory use cases.  Last I looked there's nothing defined / implemented.

When I reviewed the cxl.mem protocol about a year or so ago, I came away
thinking a deep flush was going to be problematic for shared devices
(multiple separate coherency domains / non-coherent memory).

~Gregory