On 9/2/22 10:39 AM, Wei Xu wrote: > On Thu, Sep 1, 2022 at 5:33 PM Huang, Ying <ying.huang@xxxxxxxxx> wrote: >> >> Aneesh Kumar K V <aneesh.kumar@xxxxxxxxxxxxx> writes: >> >>> On 9/1/22 12:31 PM, Huang, Ying wrote: >>>> "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> writes: >>>> >>>>> This patch adds /sys/devices/virtual/memory_tiering/ where all memory tier >>>>> related details can be found. All allocated memory tiers will be listed >>>>> there as /sys/devices/virtual/memory_tiering/memory_tierN/ >>>>> >>>>> The nodes which are part of a specific memory tier can be listed via >>>>> /sys/devices/virtual/memory_tiering/memory_tierN/nodes >>>> >>>> I think "memory_tier" is a better subsystem/bus name than >>>> memory_tiering. Because we have a set of memory_tierN devices inside. >>>> "memory_tier" sounds more natural. I know this is subjective, just my >>>> preference. >>>> I missed replying to this earlier. I will keep memory_tiering as subsystem name in v4 because we would want it to a susbsystem where all memory tiering related details can be found including memory type in the future. This is as per discussion https://lore.kernel.org/linux-mm/CAAPL-u9TKbHGztAF=r-io3gkX7gorUunS2UfstudCWuihrA=0g@xxxxxxxxxxxxxx >>>>> >>>>> A directory hierarchy looks like >>>>> :/sys/devices/virtual/memory_tiering$ tree memory_tier4/ >>>>> memory_tier4/ >>>>> ├── nodes >>>>> ├── subsystem -> ../../../../bus/memory_tiering >>>>> └── uevent >>>>> >>>>> All toptier nodes are listed via >>>>> /sys/devices/virtual/memory_tiering/toptier_nodes >>>>> >>>>> :/sys/devices/virtual/memory_tiering$ cat toptier_nodes >>>>> 0,2 >>>>> :/sys/devices/virtual/memory_tiering$ cat memory_tier4/nodes >>>>> 0,2 >>>> >>>> I don't think that it is a good idea to show toptier information in user >>>> space interface. Because it is just a in kernel implementation >>>> details. Now, we only promote pages from !toptier to toptier. But >>>> there may be multiple memory tiers in toptier and !toptier, we may >>>> change the implementation in the future. For example, we may promote >>>> pages from DRAM to HBM in the future. >>>> >>> >>> >>> In the case you describe above and others, we will always have a list of >>> NUMA nodes from which memory promotion is not done. >>> /sys/devices/virtual/memory_tiering/toptier_nodes shows that list. >> >> I don't think we will need that interface if we don't restrict promotion >> in the future. For example, he can just check the memory tier with >> smallest number. >> >> TBH, I don't know why do we need that interface. What is it for? We >> don't want to expose unnecessary information to restrict our in kernel >> implementation in the future. >> >> So, please remove that interface at least before we discussing it >> thoroughly. > > I have asked for this interface to allow the userspace to query a list > of top-tier nodes as the targets of userspace-driven promotions. The > idea is that demotion can gradually go down tier by tier, but we > promote hot pages directly to the top-tier and bypass the immediate > tiers. > > Certainly, this can be viewed as a policy choice. Given that now we > have a clearly defined memory tier hierarchy in sysfs and the > toptier_nodes content can be constructed from this memory tier > hierarchy and other information from the node sysfs interfaces, I am > fine if we want to remove toptier_nodes and keep the current memory > tier sysfs interfaces to the minimal. > Ok I can do a v4 with toptier_nodes dropped. -aneesh
