On Thu, Apr 7, 2022 at 4:11 PM Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> wrote: > > On Thu, 2022-04-07 at 15:12 -0700, Wei Xu wrote: > > > > > (resending in plain-text, sorry). > > > > memory.demote can work with any level of memory tiers if a nodemask > > argument (or a tier argument if there is a more-explicitly defined, > > userspace visible tiering representation) is provided. The semantics > > can be to demote X bytes from these nodes to their next tier. > > > > We do need some kind of userspace visible tiering representation. > Will be nice if I can tell the memory type, nodemask of nodes in tier Y with > > cat memory.tier_Y > > > > memory_dram/memory_pmem assumes the hardware for a particular memory > > tier, which is undesirable. For example, it is entirely possible that > > a slow memory tier is implemented by a lower-cost/lower-performance > > DDR device connected via CXL.mem, not by PMEM. It is better for this > > interface to speak in either the NUMA node abstraction or a new tier > > abstraction. > > Just from the perspective of memory.reclaim and memory.demote, I think > they could work with nodemask. For ease of management, > some kind of abstraction of tier information like nodemask, memory type > and expected performance should be readily accessible by user space. > I agree. The tier information should be provided at the system level. One suggestion is to have a new directory "/sys/devices/system/tier/" for tiers, e.g.: /sys/devices/system/tier/tier0/memlist: all memory nodes in tier 0. /sys/devices/system/tier/tier1/memlist: all memory nodes in tier 1. We can discuss this tier representation in a new thread. > Tim > > > > > It is also desirable to make this interface stateless, i.e. not to > > require the setting of memory_dram.reclaim_policy. Any policy can be > > specified as arguments to the request itself and should only affect > > that particular request. > > > > Wei >
