Gregory Price <gregory.price@xxxxxxxxxxxx> writes: > On Tue, Apr 11, 2023 at 02:37:50PM +0800, Huang, Ying wrote: >> Gregory Price <gregory.price@xxxxxxxxxxxx> writes: >> >> [snip] >> >> > 2. During the migration process, the memory needs to be forced not to be >> > migrated to another node by other means (tiering software, swap, >> > etc). The obvious way of doing this would be to migrate and >> > temporarily pin the page... but going back to problem #1 we see that >> > ZONE_MOVABLE and Pinning are mutually exclusive. So that's >> > troublesome. >> >> Can we use memory policy (cpusets, mbind(), set_mempolicy(), etc.) to >> avoid move pages out of CXL.mem node? Now, there are gaps in tiering, >> but I think it is fixable. >> >> Best Regards, >> Huang, Ying >> >> [snip] > > That feels like a hack/bodge rather than a proper solution to me. > > Maybe this is an affirmative argument for the creation of an EXMEM > zone. Let's start with requirements. What is the requirements for a new zone type? > Specifically to allow page pinning, but with far more stringent > controls - > i.e. the zone is excluded from use via general allocations. This can also be controlled via memory policy. The alternative solution is to add a per node attribute. > The point of ZONE_MOVABLE is to allow general allocation of userland > data into hotpluggable memory regions. IIUC, one typical requirement of CXL.mem is hotpluggable, right? Best Regards, Huang, Ying > This memory region is not for general use, and wants to allow pinning > and be hotpluggable under very controlled circumstances. That seems > like a reasonable argument for the creation of EXMEM. > > ~Gregory
