[PATCH RFC] KVM: use kmalloc() for small dirty bitmaps

[Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>]

** NOT TESTED WELL YET **

Currently, we are using vmalloc() for all dirty bitmaps even though
they are small enough, say 256 bytes or less.

So we use kmalloc() if dirty bitmap size is less than or equal to
PAGE_SIZE.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>
---
 arch/x86/kvm/x86.c       |    4 ++--
 include/linux/kvm_host.h |   24 ++++++++++++++++++++++++
 virt/kvm/kvm_main.c      |    6 +++---
 3 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f3f86b2..e137c34 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3172,7 +3172,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 		spin_unlock(&kvm->mmu_lock);
 
 		r = -ENOMEM;
-		dirty_bitmap = vmalloc(n);
+		dirty_bitmap = kvm_alloc_dirty_bitmap(n);
 		if (!dirty_bitmap)
 			goto out;
 		memset(dirty_bitmap, 0, n);
@@ -3197,7 +3197,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 			vfree(dirty_bitmap);
 			goto out;
 		}
-		vfree(dirty_bitmap);
+		kvm_free_dirty_bitmap(dirty_bitmap, n);
 	} else {
 		r = -EFAULT;
 		if (clear_user(log->dirty_bitmap, n))
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 0b89d00..fe19118 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -14,6 +14,8 @@
 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/mm.h>
+#include <linux/vmalloc.h>
+#include <linux/slab.h>
 #include <linux/preempt.h>
 #include <linux/msi.h>
 #include <asm/signal.h>
@@ -133,6 +135,28 @@ static inline unsigned long kvm_dirty_bitmap_bytes(struct kvm_memory_slot *memsl
 	return ALIGN(memslot->npages, BITS_PER_LONG) / 8;
 }
 
+/*
+ * Dirty bitmap allocation function.
+ * Some memslots don't need so long bitmaps and we can eliminate vmalloc()
+ * for them.
+ */
+static inline unsigned long *kvm_alloc_dirty_bitmap(unsigned long bytes)
+{
+	if (bytes < PAGE_SIZE)
+		return kmalloc(bytes, GFP_KERNEL);
+	else
+		return vmalloc(bytes);
+}
+
+static inline void kvm_free_dirty_bitmap(unsigned long *dirty_bitmap,
+					 unsigned long bytes)
+{
+	if (bytes < PAGE_SIZE)
+		kfree(dirty_bitmap);
+	else
+		vfree(dirty_bitmap);
+}
+
 struct kvm_kernel_irq_routing_entry {
 	u32 gsi;
 	u32 type;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1aeeb7f..1a8ba85 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -454,8 +454,8 @@ static void kvm_free_physmem_slot(struct kvm_memory_slot *free,
 		vfree(free->rmap);
 
 	if (!dont || free->dirty_bitmap != dont->dirty_bitmap)
-		vfree(free->dirty_bitmap);
-
+		kvm_free_dirty_bitmap(free->dirty_bitmap,
+				      kvm_dirty_bitmap_bytes(free));
 
 	for (i = 0; i < KVM_NR_PAGE_SIZES - 1; ++i) {
 		if (!dont || free->lpage_info[i] != dont->lpage_info[i]) {
@@ -663,7 +663,7 @@ skip_lpage:
 	if ((new.flags & KVM_MEM_LOG_DIRTY_PAGES) && !new.dirty_bitmap) {
 		unsigned long dirty_bytes = kvm_dirty_bitmap_bytes(&new);
 
-		new.dirty_bitmap = vmalloc(dirty_bytes);
+		new.dirty_bitmap = kvm_alloc_dirty_bitmap(dirty_bytes);
 		if (!new.dirty_bitmap)
 			goto out_free;
 		memset(new.dirty_bitmap, 0, dirty_bytes);
-- 
1.7.0.4

--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html