On Tue, May 24, 2022 at 6:27 AM Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> wrote: > > Wei Xu <weixugc@xxxxxxxxxx> writes: > > > On Wed, May 18, 2022 at 5:00 AM Jonathan Cameron > > <Jonathan.Cameron@xxxxxxxxxx> wrote: > >> > >> On Wed, 18 May 2022 00:09:48 -0700 > >> Wei Xu <weixugc@xxxxxxxxxx> wrote: > > ... > > > Nice :) > >> > >> Initially I thought this was over complicated when compared to just leaving space, but > >> after a chat with Hesham just now you have us both convinced that this is an elegant solution. > >> > >> Few corners probably need fleshing out: > >> * Use of an allocator for new tiers. Flat number at startup, or new one on write of unique > >> value to set_memtier perhaps? Also whether to allow drivers to allocate (I think > >> we should). > >> * Multiple tiers with same rank. My assumption is from demotion path point of view you > >> fuse them (treat them as if they were a single tier), but keep them expressed > >> separately in the sysfs interface so that the rank can be changed independently. > >> * Some guidance on what values make sense for given rank default that might be set by > >> a driver. If we have multiple GPU vendors, and someone mixes them in a system we > >> probably don't want the default values they use to result in demotion between them. > >> This might well be a guidance DOC or appropriate set of #define > > > > All of these are good ideas, though I am afraid that these can make > > tier management too complex for what it's worth. > > > > How about an alternative tier numbering scheme that uses major.minor > > device IDs? For simplicity, we can just start with 3 major tiers. > > New tiers can be inserted in-between using minor tier IDs. > > > What drives the creation of a new memory tier here? Jonathan was > suggesting we could do something similar to writing to set_memtier for > creating a new memory tier. > > $ echo "memtier128" > sys/devices/system/node/node1/set_memtier > > But I am wondering whether we should implement that now. If we keep > "rank" concept and detach tier index (memtier0 is the memory tier with > index 0) separate from rank, I assume we have enough flexibility for a > future extension that will allow us to create a memory tier from userspace > and assigning it a rank value that helps the device to be placed before or > after DRAM in demotion order. > > ie, For now we will only have memtier0, memtier1, memtier2. We won't add > dynamic creation of memory tiers and the above memory tiers will have > rank value 0, 1, 2 according with demotion order 0 -> 1 -> 2. Great. So the consensus is to go with the "rank" approach. The above sounds good to me as a starting point. > -aneesh
