Wei Xu <weixugc@xxxxxxxxxx> writes: > 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. >> >> >> >>> >> >>> 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. Yes. It's possible for us to change this in the future. > 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. Thanks! Best Regards, Huang, Ying >> >> Do we need a way to show the default memory tier in sysfs? That is, the >> >> memory tier that the DRAM nodes belong to. >> >> >> > >> > I will hold adding that until we have support for modifying memory tier details from >> > userspace. That is when userspace would want to know about the default memory tier. >> > >> > For now, the user interface is a simpler hierarchy of memory tiers, it's associated >> > nodes and the list of nodes from which promotion is not done. >> >> OK. >> >> Best Regards, >> Huang, Ying
