Re: [Qemu-devel] [PATCH] qemu_vmalloc: align properly for transparent hugepages and KVM

[Anthony Liguori]

On 09/05/2011 03:07 AM, Avi Kivity wrote:

To make good use of transparent hugepages, KVM requires that guest-physical
and host-virtual addresses share the low 21 bits (as opposed to just the low
12 bits normally required).

Adjust qemu_vmalloc() to honor that requirement.  Ignore it for small regions
to avoid fragmentation.

Signed-off-by: Avi Kivity<a...@redhat.com>

Applied.  Thanks.

Regards,

Anthony Liguori

---
  oslib-posix.c |   14 +++++++++++++-
  1 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/oslib-posix.c b/oslib-posix.c
index 196099c..a304fb0 100644
--- a/oslib-posix.c
+++ b/oslib-posix.c
@@ -35,6 +35,13 @@
  extern int daemon(int, int);
  #endif

+#if defined(__linux__)&&  defined(__x86_64__)
+   /* Use 2MB alignment so transparent hugepages can be used by KVM */
+#  define QEMU_VMALLOC_ALIGN (512 * 4096)
+#else
+#  define QEMU_VMALLOC_ALIGN getpagesize()
+#endif
+
  #include "config-host.h"
  #include "sysemu.h"
  #include "trace.h"
@@ -80,7 +87,12 @@ int qemu_daemon(int nochdir, int noclose)
  void *qemu_vmalloc(size_t size)
  {
      void *ptr;
-    ptr = qemu_memalign(getpagesize(), size);
+    size_t align = QEMU_VMALLOC_ALIGN;
+
+    if (size<  align) {
+        align = getpagesize();
+    }
+    ptr = qemu_memalign(align, size);
      trace_qemu_vmalloc(size, ptr);
      return ptr;
  }