On Mon, Apr 21, 2025 at 10:55:25AM -0400, Pasha Tatashin wrote: > On Sun, Apr 20, 2025 at 10:06 PM Ira Weiny <ira.weiny@xxxxxxxxx> wrote: > > > > Michal Clapinski wrote: > > > Currently, the user has to specify each memory region to be used with > > > nvdimm via the memmap parameter. Due to the character limit of the > > > command line, this makes it impossible to have a lot of pmem devices. > > > This new parameter solves this issue by allowing users to divide > > > one e820 entry into many nvdimm regions. > > > > > > This change is needed for the hypervisor live update. VMs' memory will > > > be backed by those emulated pmem devices. To support various VM shapes > > > I want to create devdax devices at 1GB granularity similar to hugetlb. > > > > Why is it not sufficient to create a region out of a single memmap range > > and create multiple 1G dax devices within that single range? > > This method implies using the ndctl tool to create regions and convert > them to dax devices from userspace. This does not work for our use > case. We must have these 1 GB regions available during boot because we > do not want to lose memory for a devdax label. I.e., if fsdax is > created during boot (i.e. default pmem format), it does not have a > label. However, if it is created from userspace, we create a label > with partition properties, UUID, etc. Here, we need to use kernel Doesn't ndctl refuse to alter namespaces on "legacy" (i.e. memmap=) regions? > parameters to specify the properties of the pmem devices during boot > so they can persist across reboots without losing any memory to > labels. > > Pasha -- Sincerely yours, Mike.
