On Thu, May 12, 2022 at 2:13 PM Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> wrote: > > On Thu, 2022-05-12 at 01:15 -0700, Wei Xu wrote: > > > > I am OK with moving back the memory tier nodelist into node/. When > > there are more memory tier attributes needed, we can then create the > > memory tier subtree and replace the tier nodelist in node/ with > > symlinks. > > > > So the revised sysfs interfaces are: > > > > * /sys/devices/system/node/memory_tierN (read-only) > > > > where N = 0, 1, 2 > > > > Format: node_list > > > > * /sys/devices/system/node/nodeN/memory_tier (read/write) > > > > where N = 0, 1, ... > > > > Format: int or empty > > This looks good to me. Just wonder if having just 1 tier > lower than DRAM is sufficient. We could have wide performance > range for such secondary memories and is one tier sufficient for them? > > Tim The tier design can be extended to more than 3 tiers (e.g. via CONFIG_MAX_MEMORY_TIERS). MAX_MEMORY_TIERS is set to 3 for now because without enough memory device performance information provided by the firmware, it is difficult for the kernel to properly initialize the memory tier hierarchy beyond 3 tiers (GPU, DRAM, PMEM). We will have to resort to the userspace override to set up such many-tier systems.
