On Tue, Feb 4, 2020 at 10:20 AM Barret Rhoden <brho@xxxxxxxxxx> wrote: > > Hi - > > On 2/4/20 11:44 AM, Dan Williams wrote: > > On Tue, Feb 4, 2020 at 7:30 AM Barret Rhoden <brho@xxxxxxxxxx> wrote: > >> > >> Hi - > >> > >> On 1/10/20 2:03 PM, Joao Martins wrote: > >>> User can define regions with 'memmap=size!offset' which in turn > >>> creates PMEM legacy devices. But because it is a label-less > >>> NVDIMM device we only have one namespace for the whole device. > >>> > >>> Add support for multiple namespaces by adding ndctl control > >>> support, and exposing a minimal set of features: > >>> (ND_CMD_GET_CONFIG_SIZE, ND_CMD_GET_CONFIG_DATA, > >>> ND_CMD_SET_CONFIG_DATA) alongside NDD_ALIASING because we can > >>> store labels. > >> > >> FWIW, I like this a lot. If we move away from using memmap in favor of > >> efi_fake_mem, ideally we'd have the same support for full-fledged > >> pmem/dax regions and namespaces that this patch brings. > > > > No, efi_fake_mem only supports creating dax-regions. What's the use > > case that can't be satisfied by just specifying multiple memmap= > > ranges? > > I'd like to be able to create and destroy dax regions on the fly. In > particular, I want to run guest VMs using the dax files for guest > memory, but I don't know at boot time how many VMs I'll have, or what > their sizes are. Ideally, I'd have separate files for each VM, instead > of a single /dev/dax. > > I currently do this with fs-dax with one big memmap region (ext4 on > /dev/pmem0), and I use the file system to handle the > creation/destruction/resizing and metadata management. But since fs-dax > won't work with device pass-through, I started looking at dev-dax, with > the expectation that I'd need some software to manage the memory (i.e. > allocation). That led me to ndctl, which seems to need namespace labels > to have the level of control I was looking for. Ah, got it, you only ended up at wanting namespace labels because there was no other way to carve up device-dax. That's changing as part of the efi_fake_mem= enabling and I have a patch set in the works to allow discontiguous sub-divisions of a device-dax range. Note that is this branch rebases frequently: https://git.kernel.org/pub/scm/linux/kernel/git/djbw/nvdimm.git/log/?h=libnvdimm-pending > > Thanks, > > Barret >
