32 #include "utilities/powerOfTwo.hpp"
33
34 void ZHeuristics::set_medium_page_size() {
35 // Set ZPageSizeMedium so that a medium page occupies at most 3.125% of the
36 // max heap size. ZPageSizeMedium is initially set to 0, which means medium
37 // pages are effectively disabled. It is adjusted only if ZPageSizeMedium
38 // becomes larger than ZPageSizeSmall.
39 const size_t min = ZGranuleSize;
40 const size_t max = ZGranuleSize * 16;
41 const size_t unclamped = MaxHeapSize * 0.03125;
42 const size_t clamped = clamp(unclamped, min, max);
43 const size_t size = round_down_power_of_2(clamped);
44
45 if (size > ZPageSizeSmall) {
46 // Enable medium pages
47 ZPageSizeMedium = size;
48 ZPageSizeMediumShift = log2_intptr(ZPageSizeMedium);
49 ZObjectSizeLimitMedium = ZPageSizeMedium / 8;
50 ZObjectAlignmentMediumShift = (int)ZPageSizeMediumShift - 13;
51 ZObjectAlignmentMedium = 1 << ZObjectAlignmentMediumShift;
52
53 log_info(gc, init)("Medium Page Size: " SIZE_FORMAT "M", ZPageSizeMedium / M);
54 } else {
55 log_info(gc, init)("Medium Page Size: N/A");
56 }
57 }
58
59 bool ZHeuristics::use_per_cpu_shared_small_pages() {
60 // Use per-CPU shared small pages only if these pages occupy at most 3.125%
61 // of the max heap size. Otherwise fall back to using a single shared small
62 // page. This is useful when using small heaps on large machines.
63 const size_t per_cpu_share = (MaxHeapSize * 0.03125) / ZCPU::count();
64 return per_cpu_share >= ZPageSizeSmall;
65 }
66
67 static uint nworkers_based_on_ncpus(double cpu_share_in_percent) {
68 return ceil(os::initial_active_processor_count() * cpu_share_in_percent / 100.0);
69 }
70
71 static uint nworkers_based_on_heap_size(double reserve_share_in_percent) {
72 const int nworkers = (MaxHeapSize * (reserve_share_in_percent / 100.0)) / ZPageSizeSmall;
73 return MAX2(nworkers, 1);
74 }
75
76 static uint nworkers(double cpu_share_in_percent) {
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32 #include "utilities/powerOfTwo.hpp"
33
34 void ZHeuristics::set_medium_page_size() {
35 // Set ZPageSizeMedium so that a medium page occupies at most 3.125% of the
36 // max heap size. ZPageSizeMedium is initially set to 0, which means medium
37 // pages are effectively disabled. It is adjusted only if ZPageSizeMedium
38 // becomes larger than ZPageSizeSmall.
39 const size_t min = ZGranuleSize;
40 const size_t max = ZGranuleSize * 16;
41 const size_t unclamped = MaxHeapSize * 0.03125;
42 const size_t clamped = clamp(unclamped, min, max);
43 const size_t size = round_down_power_of_2(clamped);
44
45 if (size > ZPageSizeSmall) {
46 // Enable medium pages
47 ZPageSizeMedium = size;
48 ZPageSizeMediumShift = log2_intptr(ZPageSizeMedium);
49 ZObjectSizeLimitMedium = ZPageSizeMedium / 8;
50 ZObjectAlignmentMediumShift = (int)ZPageSizeMediumShift - 13;
51 ZObjectAlignmentMedium = 1 << ZObjectAlignmentMediumShift;
52 }
53 }
54
55 size_t ZHeuristics::max_reserve() {
56 // Reserve one small page per worker plus one shared medium page. This is still just
57 // an estimate and doesn't guarantee that we can't run out of memory during relocation.
58 const uint nworkers = MAX2(ParallelGCThreads, ConcGCThreads);
59 const size_t reserve = (nworkers * ZPageSizeSmall) + ZPageSizeMedium;
60 return MIN2(MaxHeapSize, reserve);
61 }
62
63 bool ZHeuristics::use_per_cpu_shared_small_pages() {
64 // Use per-CPU shared small pages only if these pages occupy at most 3.125%
65 // of the max heap size. Otherwise fall back to using a single shared small
66 // page. This is useful when using small heaps on large machines.
67 const size_t per_cpu_share = (MaxHeapSize * 0.03125) / ZCPU::count();
68 return per_cpu_share >= ZPageSizeSmall;
69 }
70
71 static uint nworkers_based_on_ncpus(double cpu_share_in_percent) {
72 return ceil(os::initial_active_processor_count() * cpu_share_in_percent / 100.0);
73 }
74
75 static uint nworkers_based_on_heap_size(double reserve_share_in_percent) {
76 const int nworkers = (MaxHeapSize * (reserve_share_in_percent / 100.0)) / ZPageSizeSmall;
77 return MAX2(nworkers, 1);
78 }
79
80 static uint nworkers(double cpu_share_in_percent) {
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