KVM: use kmalloc() for small dirty bitmaps

Currently we are using vmalloc() for all dirty bitmaps even if
they are small enough, say less than K bytes.

We use kmalloc() if dirty bitmap size is less than or equal to
PAGE_SIZE so that we can avoid vmalloc area usage for VGA.

This will also make the logging start/stop faster.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 27649fdaa007..9ce1079e8f89 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -449,7 +449,11 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot)
         if (!memslot->dirty_bitmap)
                 return;
 
-        vfree(memslot->dirty_bitmap_head);
+        if (2 * kvm_dirty_bitmap_bytes(memslot) > PAGE_SIZE)
+                vfree(memslot->dirty_bitmap_head);
+        else
+                kfree(memslot->dirty_bitmap_head);
+
         memslot->dirty_bitmap = NULL;
         memslot->dirty_bitmap_head = NULL;
 }
@@ -547,11 +551,14 @@ static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot)
 {
         unsigned long dirty_bytes = 2 * kvm_dirty_bitmap_bytes(memslot);
 
-        memslot->dirty_bitmap = vmalloc(dirty_bytes);
+        if (dirty_bytes > PAGE_SIZE)
+                memslot->dirty_bitmap = vzalloc(dirty_bytes);
+        else
+                memslot->dirty_bitmap = kzalloc(dirty_bytes, GFP_KERNEL);
+
         if (!memslot->dirty_bitmap)
                 return -ENOMEM;
 
-        memset(memslot->dirty_bitmap, 0, dirty_bytes);
         memslot->dirty_bitmap_head = memslot->dirty_bitmap;
         return 0;
 }