Messages in this thread | | | Date | Mon, 6 Jun 2022 14:03:21 +0530 | Subject | Re: [PATCH v5 9/9] mm/demotion: Update node_is_toptier to work with memory tiers | From | Aneesh Kumar K V <> |
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On 6/6/22 12:54 PM, Ying Huang wrote: > On Mon, 2022-06-06 at 09:22 +0530, Aneesh Kumar K V wrote: >> On 6/6/22 8:41 AM, Ying Huang wrote: >>> On Fri, 2022-06-03 at 19:12 +0530, Aneesh Kumar K.V wrote: >>>> With memory tiers support we can have memory on NUMA nodes >>>> in the top tier from which we want to avoid promotion tracking NUMA >>>> faults. Update node_is_toptier to work with memory tiers. To >>>> avoid taking locks, a nodemask is maintained for all demotion >>>> targets. All NUMA nodes are by default top tier nodes and as >>>> we add new lower memory tiers NUMA nodes get added to the >>>> demotion targets thereby moving them out of the top tier. >>> >>> Check the usage of node_is_toptier(), >>> >>> - migrate_misplaced_page() >>> node_is_toptier() is used to check whether migration is a promotion. >>> We can avoid to use it. Just compare the rank of the nodes. >>> >>> - change_pte_range() and change_huge_pmd() >>> node_is_toptier() is used to avoid scanning fast memory (DRAM) pages >>> for promotion. So I think we should change the name to node_is_fast() >>> as follows, >>> >>> static inline bool node_is_fast(int node) >>> { >>> return NODE_DATA(node)->mt_rank >= MEMORY_RANK_DRAM; >>> } >>> >> >> But that gives special meaning to MEMORY_RANK_DRAM. As detailed in other >> patches, absolute value of rank doesn't carry any meaning. It is only >> the relative value w.r.t other memory tiers that decide whether it is >> fast or not. Agreed by default memory tiers get built with >> MEMORY_RANK_DRAM. But userspace can change the rank value of 'memtier1' >> Hence to determine a node is consisting of fast memory is essentially >> figuring out whether node is the top most tier in memory hierarchy and >> not just the memory tier rank value is >= MEMORY_RANK_DRAM? > > In a system with 3 tiers, > > HBM 0 > DRAM 1 > PMEM 2 > > In your implementation, only HBM will be considered fast. But what we > need is to consider both HBM and DRAM fast. Because we use NUMA > balancing to promote PMEM pages to DRAM. It's unnecessary to scan HBM > and DRAM pages for that. And there're no requirements to promote DRAM > pages to HBM with NUMA balancing. > > I can understand that the memory tiers are more dynamic now. For > requirements of NUMA balancing, we need the lowest memory tier (rank) > where there's at least one node with CPU. The nodes in it and the > higher tiers will be considered fast. >
is this good (not tested)? /* * build the allowed promotion mask. Promotion is allowed * from higher memory tier to lower memory tier only if * lower memory tier doesn't include compute. We want to * skip promotion from a memory tier, if any node which is * part of that memory tier have CPUs. Once we detect such * a memory tier, we consider that tier as top tier from * which promotion is not allowed. */ list_for_each_entry_reverse(memtier, &memory_tiers, list) { nodes_and(allowed, node_state[N_CPU], memtier->nodelist); if (nodes_empty(allowed)) nodes_or(promotion_mask, promotion_mask, allowed); else break; }
and then
static inline bool node_is_toptier(int node) {
return !node_isset(node, promotion_mask); }
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