From 1890d85c0e647d3f890e3c7152f8cd2e60dfd826 Mon Sep 17 00:00:00 2001
From: Per Liden <pliden@openjdk.org>
Date: Fri, 17 Sep 2021 07:51:45 +0000
Subject: [PATCH] 8273872: ZGC: Explicitly use 2M large pages

Reviewed-by: eosterlund, tschatzl, stefank
---
 .../gc/z/zPhysicalMemoryBacking_linux.cpp      | 18 +++++++++---------
 src/hotspot/share/gc/z/zArguments.cpp          |  7 +++++++
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/hotspot/os/linux/gc/z/zPhysicalMemoryBacking_linux.cpp b/src/hotspot/os/linux/gc/z/zPhysicalMemoryBacking_linux.cpp
index 7a113055423aa..951b98d6cce40 100644
--- a/src/hotspot/os/linux/gc/z/zPhysicalMemoryBacking_linux.cpp
+++ b/src/hotspot/os/linux/gc/z/zPhysicalMemoryBacking_linux.cpp
@@ -58,6 +58,9 @@
 #ifndef MFD_HUGETLB
 #define MFD_HUGETLB                      0x0004U
 #endif
+#ifndef MFD_HUGE_2MB
+#define MFD_HUGE_2MB                     0x54000000U
+#endif
 
 // open(2) flags
 #ifndef O_CLOEXEC
@@ -175,12 +178,6 @@ ZPhysicalMemoryBacking::ZPhysicalMemoryBacking(size_t max_capacity) :
     return;
   }
 
-  if (ZLargePages::is_explicit() && os::large_page_size() != ZGranuleSize) {
-    log_error_p(gc)("Incompatible large page size configured " SIZE_FORMAT " (expected " SIZE_FORMAT ")",
-                    os::large_page_size(), ZGranuleSize);
-    return;
-  }
-
   // Make sure the filesystem block size is compatible
   if (ZGranuleSize % _block_size != 0) {
     log_error_p(gc)("Filesystem backing the heap has incompatible block size (" SIZE_FORMAT ")",
@@ -199,17 +196,20 @@ ZPhysicalMemoryBacking::ZPhysicalMemoryBacking(size_t max_capacity) :
 }
 
 int ZPhysicalMemoryBacking::create_mem_fd(const char* name) const {
+  assert(ZGranuleSize == 2 * M, "Granule size must match MFD_HUGE_2MB");
+
   // Create file name
   char filename[PATH_MAX];
   snprintf(filename, sizeof(filename), "%s%s", name, ZLargePages::is_explicit() ? ".hugetlb" : "");
 
   // Create file
-  const int extra_flags = ZLargePages::is_explicit() ? MFD_HUGETLB : 0;
+  const int extra_flags = ZLargePages::is_explicit() ? (MFD_HUGETLB | MFD_HUGE_2MB) : 0;
   const int fd = ZSyscall::memfd_create(filename, MFD_CLOEXEC | extra_flags);
   if (fd == -1) {
     ZErrno err;
     log_debug_p(gc, init)("Failed to create memfd file (%s)",
-                          ((ZLargePages::is_explicit() && err == EINVAL) ? "Hugepages not supported" : err.to_string()));
+                          (ZLargePages::is_explicit() && (err == EINVAL || err == ENODEV)) ?
+                          "Hugepages (2M) not available" : err.to_string());
     return -1;
   }
 
@@ -445,7 +445,7 @@ ZErrno ZPhysicalMemoryBacking::fallocate_compat_mmap_tmpfs(size_t offset, size_t
   }
 
   // Advise mapping to use transparent huge pages
-  os::realign_memory((char*)addr, length, os::large_page_size());
+  os::realign_memory((char*)addr, length, ZGranuleSize);
 
   // Touch the mapping (safely) to make sure it's backed by memory
   const bool backed = safe_touch_mapping(addr, length, _block_size);
diff --git a/src/hotspot/share/gc/z/zArguments.cpp b/src/hotspot/share/gc/z/zArguments.cpp
index e22db0c52a8be..ad59d2fbcecfb 100644
--- a/src/hotspot/share/gc/z/zArguments.cpp
+++ b/src/hotspot/share/gc/z/zArguments.cpp
@@ -72,6 +72,13 @@ void ZArguments::initialize() {
     vm_exit_during_initialization("The flag -XX:+UseZGC can not be combined with -XX:ConcGCThreads=0");
   }
 
+  // Large page size must match granule size
+  if (!FLAG_IS_DEFAULT(LargePageSizeInBytes) && LargePageSizeInBytes != ZGranuleSize) {
+    vm_exit_during_initialization(err_msg("Incompatible -XX:LargePageSizeInBytes, only "
+                                          SIZE_FORMAT "M large pages are supported by ZGC",
+                                          ZGranuleSize / M));
+  }
+
   // The heuristics used when UseDynamicNumberOfGCThreads is
   // enabled defaults to using a ZAllocationSpikeTolerance of 1.
   if (UseDynamicNumberOfGCThreads && FLAG_IS_DEFAULT(ZAllocationSpikeTolerance)) {