Why do functions like similar and copy make 2 allocations for large arrays?

sgaure · July 19, 2024, 8:50am

There is slightly different treatment of memory smaller and larger than 2048:

JuliaLang/julia/blob/0e6d7972c62eb1dedaf00ea9b966a0060e2effb8/src/genericmemory.c#L51C4-L64C1


      
          int pooled = tot <= GC_MAX_SZCLASS;
          if (!pooled) {
              data = (char*)jl_gc_managed_malloc(prod);
              tot = sizeof(jl_genericmemory_t) + sizeof(void*);
          }
          m = (jl_genericmemory_t*)jl_gc_alloc(ct->ptls, tot, mtype);
          if (pooled) {
              data = (char*)m + JL_SMALL_BYTE_ALIGNMENT;
          }
          else {
              int isaligned = 1; // jl_gc_managed_malloc is always aligned
              jl_gc_track_malloced_genericmemory(ct->ptls, m, isaligned);
              jl_genericmemory_data_owner_field(m) = (jl_value_t*)m;
          }

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Why do functions like similar and copy make 2 allocations for large arrays?

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