8257076: os::scan_pages is empty on all platforms

Reviewed-by: dholmes, stuefe

src/hotspot/os/aix/os_aix.cpp

@@ -1914,10 +1914,6 @@ bool os::numa_get_group_ids_for_range(const void** addresses, int* lgrp_ids, siz
   return false;
 }
 
-char *os::scan_pages(char *start, char* end, page_info* page_expected, page_info* page_found) {
-  return end;
-}
-
 // Reserves and attaches a shared memory segment.
 char* os::pd_reserve_memory(size_t bytes, bool exec) {
   // Always round to os::vm_page_size(), which may be larger than 4K.

src/hotspot/os/bsd/os_bsd.cpp

@@ -1674,11 +1674,6 @@ bool os::numa_get_group_ids_for_range(const void** addresses, int* lgrp_ids, siz
   return false;
 }
 
-char *os::scan_pages(char *start, char* end, page_info* page_expected, page_info* page_found) {
-  return end;
-}
-
-
 bool os::pd_uncommit_memory(char* addr, size_t size, bool exec) {
 #if defined(__OpenBSD__)
   // XXX: Work-around mmap/MAP_FIXED bug temporarily on OpenBSD

src/hotspot/os/linux/os_linux.cpp

@@ -3012,12 +3012,6 @@ size_t os::numa_get_leaf_groups(uint *ids, size_t size) {
   return i;
 }
 
-char *os::scan_pages(char *start, char* end, page_info* page_expected,
-                     page_info* page_found) {
-  return end;
-}
-
-
 int os::Linux::sched_getcpu_syscall(void) {
   unsigned int cpu = 0;
   long retval = -1;

src/hotspot/os/windows/os_windows.cpp

@@ -3825,11 +3825,6 @@ bool os::numa_get_group_ids_for_range(const void** addresses, int* lgrp_ids, siz
   return false;
 }
 
-char *os::scan_pages(char *start, char* end, page_info* page_expected,
-                     page_info* page_found) {
-  return end;
-}
-
 char* os::non_memory_address_word() {
   // Must never look like an address returned by reserve_memory,
   // even in its subfields (as defined by the CPU immediate fields,

src/hotspot/share/gc/parallel/mutableNUMASpace.cpp

@@ -236,20 +236,6 @@ void MutableNUMASpace::update() {
                SpaceDecorator::Clear,
                SpaceDecorator::DontMangle);
   }
-
-  scan_pages(NUMAPageScanRate);
-}
-
-// Scan pages. Free pages that have smaller size or wrong placement.
-void MutableNUMASpace::scan_pages(size_t page_count)
-{
-  size_t pages_per_chunk = page_count / lgrp_spaces()->length();
-  if (pages_per_chunk > 0) {
-    for (int i = 0; i < lgrp_spaces()->length(); i++) {
-      LGRPSpace *ls = lgrp_spaces()->at(i);
-      ls->scan_pages(page_size(), pages_per_chunk);
-    }
-  }
 }
 
 // Accumulate statistics about the allocation rate of each lgrp.
@@ -691,43 +677,3 @@ void MutableNUMASpace::LGRPSpace::accumulate_statistics(size_t page_size) {
                                    pointer_delta(space()->end(), end, sizeof(char));
 
 }
-
-// Scan page_count pages and verify if they have the right size and right placement.
-// If invalid pages are found they are freed in hope that subsequent reallocation
-// will be more successful.
-void MutableNUMASpace::LGRPSpace::scan_pages(size_t page_size, size_t page_count)
-{
-  char* range_start = (char*)align_up(space()->bottom(), page_size);
-  char* range_end = (char*)align_down(space()->end(), page_size);
-
-  if (range_start > last_page_scanned() || last_page_scanned() >= range_end) {
-    set_last_page_scanned(range_start);
-  }
-
-  char *scan_start = last_page_scanned();
-  char* scan_end = MIN2(scan_start + page_size * page_count, range_end);
-
-  os::page_info page_expected, page_found;
-  page_expected.size = page_size;
-  page_expected.lgrp_id = checked_cast<uint>(lgrp_id());
-
-  char *s = scan_start;
-  while (s < scan_end) {
-    char *e = os::scan_pages(s, (char*)scan_end, &page_expected, &page_found);
-    if (e == nullptr) {
-      break;
-    }
-    if (e != scan_end) {
-      assert(e < scan_end, "e: " PTR_FORMAT " scan_end: " PTR_FORMAT, p2i(e), p2i(scan_end));
-
-      if ((page_expected.size != page_size || checked_cast<uint>(page_expected.lgrp_id) != lgrp_id())
-          && page_expected.size != 0) {
-        os::free_memory(s, pointer_delta(e, s, sizeof(char)), page_size);
-      }
-      page_expected = page_found;
-    }
-    s = e;
-  }
-
-  set_last_page_scanned(scan_end);
-}

src/hotspot/share/gc/parallel/mutableNUMASpace.hpp

@@ -83,11 +83,8 @@ class MutableNUMASpace : public MutableSpace {
 
     SpaceStats _space_stats;
 
-    char* _last_page_scanned;
-    char* last_page_scanned()            { return _last_page_scanned; }
-    void set_last_page_scanned(char* p)  { _last_page_scanned = p;    }
    public:
-    LGRPSpace(uint l, size_t alignment) : _lgrp_id(l), _allocation_failed(false), _last_page_scanned(nullptr) {
+    LGRPSpace(uint l, size_t alignment) : _lgrp_id(l), _allocation_failed(false) {
       _space = new MutableSpace(alignment);
       _alloc_rate = new AdaptiveWeightedAverage(NUMAChunkResizeWeight);
     }
@@ -125,7 +122,6 @@ class MutableNUMASpace : public MutableSpace {
     void clear_space_stats()                        { _space_stats = SpaceStats(); }
 
     void accumulate_statistics(size_t page_size);
-    void scan_pages(size_t page_size, size_t page_count);
   };
 
   GrowableArray<LGRPSpace*>* _lgrp_spaces;
@@ -156,8 +152,6 @@ class MutableNUMASpace : public MutableSpace {
   size_t default_chunk_size();
   // Adapt the chunk size to follow the allocation rate.
   size_t adaptive_chunk_size(int i, size_t limit);
-  // Scan and free invalid pages.
-  void scan_pages(size_t page_count);
   // Return the bottom_region and the top_region. Align them to page_size() boundary.
   // |------------------new_region---------------------------------|
   // |----bottom_region--|---intersection---|------top_region------|

src/hotspot/share/runtime/os.hpp

@@ -523,8 +523,6 @@ class os: AllStatic {
     size_t size;
     int lgrp_id;
   };
-  static char*  scan_pages(char *start, char* end, page_info* page_expected, page_info* page_found);
-
   static char*  non_memory_address_word();
   // reserve, commit and pin the entire memory region
   static char*  reserve_memory_special(size_t size, size_t alignment, size_t page_size,