lizhijian@xxxxxxxxxxx wrote:
> Hi folks,
>
> I'm going to make crash coredump support pmem region. So
> I have modified kexec-tools to add pmem region to PT_LOAD of vmcore.
>
> But it failed at makedumpfile, log are as following:
>
> In my environment, i found the last 512 pages in pmem region will cause the error.
>
> qemu commandline:
> -object memory-backend-file,id=memnvdimm0,prealloc=yes,mem-path=/root/qemu-dax.img,share=yes,size=4267704320,align=2097152
> -device nvdimm,node=0,label-size=4194304,memdev=memnvdimm0,id=nvdimm0,slot=0
>
> ndctl info:
> [root@rdma-server ~]# ndctl list
> [
> {
> "dev":"namespace0.0",
> "mode":"devdax",
> "map":"dev",
> "size":4127195136,
> "uuid":"f6fc1e86-ac5b-48d8-9cda-4888a33158f9",
> "chardev":"dax0.0",
> "align":4096
> }
> ]
> [root@rdma-server ~]# ndctl list -iRD
> {
> "dimms":[
> {
> "dev":"nmem0",
> "id":"8680-56341200",
> "handle":1,
> "phys_id":0
> }
> ],
> "regions":[
> {
> "dev":"region0",
> "size":4263510016,
> "align":16777216,
> "available_size":0,
> "max_available_extent":0,
> "type":"pmem",
> "iset_id":10248187106440278,
> "mappings":[
> {
> "dimm":"nmem0",
> "offset":0,
> "length":4263510016,
> "position":0
> }
> ],
> "persistence_domain":"unknown"
> }
> ]
> }
>
> iomem info:
> [root@rdma-server ~]# cat /proc/iomem | grep Persi
> 140000000-23e1fffff : Persistent Memory
>
> makedumpfile info:
> [ 57.229110] kdump.sh[240]: mem_map[ 71] ffffea0008e00000 238000 23e200
>
>
> Firstly, i wonder that
> 1) makedumpfile read the whole range of iomem(same with the PT_LOAD of pmem)
> 2) 1st kernel side only setup mem_map(vmemmap) for this namespace, which size is 512 pages smaller than iomem for some reasons.
> 3) Since there is an align in nvdimm region(16MiB in above), i also guess the maximum size of the pmem can used by user should
> be ALIGN(iomem, 10MiB), after this alignment, the last 512 pages will be dropped. then kernel only setups vmemmap for this
> range. but i didn't see any code doing such things in kernel side.
>
> So if you guy know the reasons, please let me know :), any hint/feedback is very welcome.
This is due to the region alignment.
2522afb86a8c libnvdimm/region: Introduce an 'align' attribute
If you want to use the full capacity it would be something like this
(untested, and may destroy any data currently on the namespace):
ndctl destroy-namespace namespace0.0
echo $((2<<20)) > /sys/bus/nd/devices/region0/align
ndctl create-namespace -m dax -a 4k -M mem
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