Re: [QEMU-devel][RFC PATCH 1/1] backends/hostmem: qapi/qom: Add an ObjectOption for memory-backend-* called HostMemType and its arg 'cxlram'

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Jack,

On 1/1/24 08:53, Ho-Ren (Jack) Chuang wrote:
> Introduce a new configuration option 'host-mem-type=' in the
> '-object memory-backend-ram', allowing users to specify
> from which type of memory to allocate.
> 
> Users can specify 'cxlram' as an argument, and QEMU will then
> automatically locate CXL RAM NUMA nodes and use them as the backend memory.
> For example:
> 	-object memory-backend-ram,id=vmem0,size=19G,host-mem-type=cxlram \
> 	-device pxb-cxl,bus_nr=12,bus=pcie.0,id=cxl.1 \
> 	-device cxl-rp,port=0,bus=cxl.1,id=root_port13,chassis=0,slot=2 \
> 	-device cxl-type3,bus=root_port13,volatile-memdev=vmem0,id=cxl-vmem0 \
> 	-M cxl-fmw.0.targets.0=cxl.1,cxl-fmw.0.size=19G,cxl-fmw.0.interleave-granularity=8k \
> 
> In v1, we plan to move most of the implementations to util and break down
> this patch into different smaller patches.
> 
> Signed-off-by: Ho-Ren (Jack) Chuang <horenchuang@bytedance.com>
> Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
> ---
>   backends/hostmem.c       | 184 +++++++++++++++++++++++++++++++++++++++
>   include/sysemu/hostmem.h |   1 +
>   qapi/common.json         |  19 ++++
>   qapi/qom.json            |   1 +
>   qemu-options.hx          |   2 +-
>   5 files changed, 206 insertions(+), 1 deletion(-)
> 
> diff --git a/backends/hostmem.c b/backends/hostmem.c


> +#define CXL_DEVICE_PATH "/sys/bus/cxl/devices/"
> +#define REGION_PATH_LEN 307
> +#define DAX_REGION_PATH_LEN 563
> +#define DAX_PATH_LEN 819
> +#define TARGET_FILE_PATH_LEN 831

How do you get these numbers?

> diff --git a/qapi/common.json b/qapi/common.json
> index 6fed9cde1a..591fd73291 100644
> --- a/qapi/common.json
> +++ b/qapi/common.json
> @@ -167,6 +167,25 @@
>   { 'enum': 'HostMemPolicy',
>     'data': [ 'default', 'preferred', 'bind', 'interleave' ] }
>   
> +##
> +# @HostMemType:
> +#
> +# Automatically find a backend memory type on host.

This description is not clear (to me).

> +# Can be further extened to support other types such as cxlpmem, hbm.

Typo "extended" although I'm not sure it is helpful to mention it.

> +#
> +# @none: do nothing (default).

"do nothing" is confusing here, I'd drop it.

> +#
> +# @cxlram: a CXL RAM backend on host.
> +#
> +# Note: HostMemType and HostMemPolicy/host-nodes cannot be set at the same
> +# time. HostMemType is used to automatically bind with one kind of
> +# host memory types.
> +#
> +# Since: 8.3

9.0

> +##
> +{ 'enum': 'HostMemType',
> +  'data': [ 'none', 'cxlram' ] }
> +
>   ##
>   # @NetFilterDirection:
>   #
> diff --git a/qapi/qom.json b/qapi/qom.json
> index 95516ba325..fa3bc29708 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -626,6 +626,7 @@
>               '*host-nodes': ['uint16'],
>               '*merge': 'bool',
>               '*policy': 'HostMemPolicy',
> +            '*host-mem-type': 'HostMemType',

Missing documentation in MemoryBackendProperties.

>               '*prealloc': 'bool',
>               '*prealloc-threads': 'uint32',
>               '*prealloc-context': 'str',