Messages in this thread | | | Date | Wed, 27 Apr 2022 08:27:19 +0530 | Subject | Re: [PATCH v3 0/7] mm: demotion: Introduce new node state N_DEMOTION_TARGETS | From | Aneesh Kumar K V <> |
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On 4/27/22 6:59 AM, ying.huang@intel.com wrote: > On Mon, 2022-04-25 at 20:14 +0530, Aneesh Kumar K V wrote: >> On 4/25/22 7:27 PM, Jonathan Cameron wrote: >>> On Mon, 25 Apr 2022 16:45:38 +0530 >>> Jagdish Gediya <jvgediya@linux.ibm.com> wrote: >>> >>>> On Sun, Apr 24, 2022 at 11:19:53AM +0800, ying.huang@intel.com wrote: >>>>> On Sat, 2022-04-23 at 01:25 +0530, Jagdish Gediya wrote: >>>>>> Some systems(e.g. PowerVM) can have both DRAM(fast memory) only >>>>>> NUMA node which are N_MEMORY and slow memory(persistent memory) >>>>>> only NUMA node which are also N_MEMORY. As the current demotion >>>>>> target finding algorithm works based on N_MEMORY and best distance, >>>>>> it will choose DRAM only NUMA node as demotion target instead of >>>>>> persistent memory node on such systems. If DRAM only NUMA node is >>>>>> filled with demoted pages then at some point new allocations can >>>>>> start falling to persistent memory, so basically cold pages are in >>>>>> fast memor (due to demotion) and new pages are in slow memory, this >>>>>> is why persistent memory nodes should be utilized for demotion and >>>>>> dram node should be avoided for demotion so that they can be used >>>>>> for new allocations. >>>>>> >>>>>> Current implementation can work fine on the system where the memory >>>>>> only numa nodes are possible only for persistent/slow memory but it >>>>>> is not suitable for the like of systems mentioned above. >>>>> >>>>> Can you share the NUMA topology information of your machine? And the >>>>> demotion order before and after your change? >>>>> >>>>> Whether it's good to use the PMEM nodes as the demotion targets of the >>>>> DRAM-only node too? >>>> >>>> $ numactl -H >>>> available: 2 nodes (0-1) >>>> node 0 cpus: 0 1 2 3 4 5 6 7 >>>> node 0 size: 14272 MB >>>> node 0 free: 13392 MB >>>> node 1 cpus: >>>> node 1 size: 2028 MB >>>> node 1 free: 1971 MB >>>> node distances: >>>> node 0 1 >>>> 0: 10 40 >>>> 1: 40 10 >>>> >>>> 1) without N_DEMOTION_TARGETS patch series, 1 is demotion target >>>> for 0 even when 1 is DRAM node and there is no demotion targets for 1. >>> >>> I'm not convinced the distinction between DRAM and persistent memory is >>> valid. There will definitely be systems with a large pool >>> of remote DRAM (and potentially no NV memory) where the right choice >>> is to demote to that DRAM pool. >>> >>> Basing the decision on whether the memory is from kmem or >>> normal DRAM doesn't provide sufficient information to make the decision. >>> >> >> Hence the suggestion for the ability to override this from userspace. >> Now, for example, we could build a system with memory from the remote >> machine (memory inception in case of power which will mostly be plugged >> in as regular hotpluggable memory ) and a slow CXL memory or OpenCAPI >> memory. >> >> In the former case, we won't consider that for demotion with this series >> because that is not instantiated via dax kmem. So yes definitely we >> would need the ability to override this from userspace so that we could >> put these remote memory NUMA nodes as demotion targets if we want. >>>> > > Is there a driver for the device (memory from the remote machine)? If > so, we can adjust demotion order for it in the driver. >
At this point, it is managed by hypervisor, is hotplugged into the the LPAR with more additional properties specified via device tree. So there is no inception specific device driver.
> In general, I think that we can adjust demotion order inside kernel from > various information sources. In addition to ACPI SLIT, we also have > HMAT, kmem driver, other drivers, etc. >
Managing inception memory will any way requires a userspace component to track the owner machine for the remote memory. So we should be ok to have userspace manage demotion order.
-aneesh
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