[PATCH] D140425: [BOLT] Fix hugify on new Linux kernels

[Maksim Panchenko via Phabricator via llvm-commits]

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Memory needs to be unlocked before madvise(2) is called for transparent
huge pages. I verified that /proc/<pid>/smaps reports FilePmdMapped
correctly. Note that there's a (non-deterministic) delay before the call
to madvise() is issued and pages are remapped. Thus, it's difficult to
test the functionality automatically.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D140425

Files:
  bolt/runtime/common.h
  bolt/runtime/hugify.cpp


Index: bolt/runtime/hugify.cpp
===================================================================
--- bolt/runtime/hugify.cpp
+++ bolt/runtime/hugify.cpp
@@ -157,6 +157,10 @@
     return;
   }
 
+  if (__munlock(From, (To - From)) == -1) {
+    char Msg[] = "[hugify] failed to unlock memory\n";
+    reportError(Msg, sizeof(Msg));
+  }
   if (__madvise(From, (To - From), 14 /* MADV_HUGEPAGE */) == -1) {
     char Msg[] = "[hugify] failed to allocate large page\n";
     // TODO: allow user to control the failure behavior.
Index: bolt/runtime/common.h
===================================================================
--- bolt/runtime/common.h
+++ bolt/runtime/common.h
@@ -422,6 +422,16 @@
   return ret;
 }
 
+int __munlock(void *addr, size_t length) {
+  int ret;
+  __asm__ __volatile__("movq $0x96, %%rax\n"
+                       "syscall\n"
+                       : "=a"(ret)
+                       : "D"(addr), "S"(length)
+                       : "cc", "rcx", "r11", "memory");
+  return ret;
+}
+
 #define _UTSNAME_LENGTH 65
 
 struct UtsNameTy {


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