commit dfeb42ede69a0dbea5735aed5fddaee3f810801d
author Elliott Hughes <enh@google.com> Mon Mar 03 20:26:12 2014 +0000
committer Gerrit Code Review <noreply-gerritcodereview@google.com> Mon Mar 03 20:26:12 2014 +0000
tree 502fe092fd17b7eddae73d1bebe417ff40a81889
parent 15e71cd760c35a4eab09b850904581ebbdc9bee3
parent 9bd9b7dd205e79577f5cd1d9488aabe0f213ce35

Merge "If the kernel doesn't have MADV_MERGEABLE, stop asking for it."

libc/bionic/mmap.cpp

diff --git a/libc/bionic/mmap.cpp b/libc/bionic/mmap.cpp
index 28a47cc..8f25a89 100644
--- a/libc/bionic/mmap.cpp
+++ b/libc/bionic/mmap.cpp
@@ -37,16 +37,23 @@
 
 #define MMAP2_SHIFT 12 // 2**12 == 4096
 
+static bool kernel_has_MADV_MERGEABLE = true;
+
 void* mmap64(void* addr, size_t size, int prot, int flags, int fd, off64_t offset) {
   if (offset < 0 || (offset & ((1UL << MMAP2_SHIFT)-1)) != 0) {
     errno = EINVAL;
     return MAP_FAILED;
   }
 
+  bool is_private_anonymous = (flags & (MAP_PRIVATE | MAP_ANONYMOUS)) != 0;
   void* result = __mmap2(addr, size, prot, flags, fd, offset >> MMAP2_SHIFT);
-  if (result != MAP_FAILED && (flags & (MAP_PRIVATE | MAP_ANONYMOUS)) != 0) {
+
+  if (result != MAP_FAILED && kernel_has_MADV_MERGEABLE && is_private_anonymous) {
     ErrnoRestorer errno_restorer;
-    madvise(result, size, MADV_MERGEABLE);
+    int rc = madvise(result, size, MADV_MERGEABLE);
+    if (rc == -1 && errno == EINVAL) {
+      kernel_has_MADV_MERGEABLE = false;
+    }
   }
 
   return result;