Wei Xu <weixugc@xxxxxxxxxx> writes: > 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. The rank approach seems good to me too. - Alistair >> -aneesh
