ksm support

Call MADV_MERGEABLE on guest memory allocations.  MADV_MERGABLE will be
available starting in Linux 2.6.32.  This system call registers a region of
virtual address space with Linux as a candidate for transparent memory
sharing.

Patchworks-ID: 35447
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

exec.c

@@ -2412,6 +2412,9 @@ ram_addr_t qemu_ram_alloc(ram_addr_t size)
     new_block = qemu_malloc(sizeof(*new_block));
 
     new_block->host = qemu_vmalloc(size);
+#ifdef MADV_MERGEABLE
+    madvise(new_block->host, size, MADV_MERGEABLE);
+#endif
     new_block->offset = last_ram_offset;
     new_block->length = size;