[PATCH 3/3 rebased-v2] KVM: use kmalloc() for small dirty bitmaps

[Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>]

I updated this one[3/3] only to use [vk]zalloc

Changelog:
  I replaced ((vmalloc | kmalloc) + memset) with (vzalloc | kzalloc).
  Also, the patch description was updated.

vzalloc() was introduced recently, so this one may be better.

BTW, I noticed that bitmaps are created/destroyed many times:
logging stop/start frequently from qemu side?

So even after the double buffering patch[2/3], this patch may have
more performance gain than I expected.

Takuya

===
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@xxxxxxxxxxxxx>
---
 virt/kvm/kvm_main.c |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8b28581..45d2cef 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;
 }
-- 
1.7.0.4

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