Re: CXL volatile memory is not listed

[Fan Ni <fan.ni@gmx.us>]

On Fri, Aug 11, 2023 at 07:52:25AM +0530, Maverickk 78 wrote:
> Thanks Fan,
>
> cxl create-region works like a charm :)
>
> Since this gets listed as "System Ram(kmem)", I guess the kernel
> treats it as regular memory and
> allocates it to the applications when needed?
> or is there an extra effort needed to make it available for
> applications on the host?
>

Yes. Once it is onlined, you can use it as regular memory.
CXL memory will serve as a zero-CPU memory-only NUMA node.
You can check it with numactl -H.

To use the cxl memory with an app, you can use
numactl --membind=numa_id app_name
#numa_id is the dedicated numa node where cxl memory sits.

One thing to notes, kvm will not work correctly with Qemu emulation when
you try to use cxl memory for an application, so do not enable kvm.

Fan

> On Thu, 10 Aug 2023 at 22:03, Fan Ni <fan.ni@gmx.us> wrote:
> >
> > On Wed, Aug 09, 2023 at 04:21:47AM +0530, Maverickk 78 wrote:
> > > Hello,
> > >
> > > I am running qemu-system-x86_64
> > >
> > > qemu-system-x86_64 --version
> > > QEMU emulator version 8.0.92 (v8.1.0-rc2-80-g0450cf0897)
> > >
> > > qemu-system-x86_64 \
> > > -m 2G,slots=4,maxmem=4G \
> > > -smp 4 \
> > > -machine type=q35,accel=kvm,cxl=on \
> > > -enable-kvm \
> > > -nographic \
> > > -device pxb-cxl,id=cxl.0,bus=pcie.0,bus_nr=52 \
> > > -device cxl-rp,id=rp0,bus=cxl.0,chassis=0,port=0,slot=0 \
> > > -object memory-backend-file,id=mem0,mem-path=/tmp/mem0,size=1G,share=true \
> > > -device cxl-type3,bus=rp0,volatile-memdev=mem0,id=cxl-mem0 \
> > > -M cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.size=1G
> > >
> > >
> > > I was expecting the CXL memory to be listed in "System Ram", the lsmem
> > > shows only 2G memory which is System RAM, it's not listing the CXL
> > > memory.
> > >
> > > Do I need to pass any particular parameter in the kernel command line?
> > >
> > > Is there any documentation available? I followed the inputs provided in
> > >
> > > https://lore.kernel.org/linux-mm/Y+CSOeHVLKudN0A6@kroah.com/T/
> > >
> > > Is there any documentation/blog listed?
> >
> > If I remember it correctly, for volatile cxl memory, we need to create a
> > region and then it will be discovered as system memory and shows up.
> >
> > Try to create a region with "cxl create-region".
> >
> > Fan
> > >