Wei Xu <weixugc@xxxxxxxxxx> writes: > 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. I think that it may be sufficient to make tier an attribute of "node". Some thing like, /sys/devices/system/node/nodeX/memory_tier Best Regards, Huang, Ying > 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 >>
