From: Takuya Yoshikawa <yoshikawa.tak...@oss.ntt.co.jp>
Although we always allocate a new dirty bitmap in x86's get_dirty_log(),
it is only used as a zero-source of copy_to_user() and freed right after
that when memslot is clean. This patch uses clear_user() instead of doing
this unnecessary zero-source allocation.
Performance improvement: as we can expect easily, the time needed to
allocate a bitmap is completely reduced. In my test, the improved ioctl
was about 4 to 10 times faster than the original one for clean slots.
Furthermore, reducing memory allocations and copies will produce good
effects to caches too.
Signed-off-by: Takuya Yoshikawa <yoshikawa.tak...@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <a...@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index dff08e5..f6f8dad 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2744,7 +2744,6 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
struct kvm_memory_slot *memslot;
unsigned long n;
unsigned long is_dirty = 0;
- unsigned long *dirty_bitmap = NULL;
mutex_lock(&kvm->slots_lock);
@@ -2759,27 +2758,30 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
n = kvm_dirty_bitmap_bytes(memslot);
- r = -ENOMEM;
- dirty_bitmap = vmalloc(n);
- if (!dirty_bitmap)
- goto out;
- memset(dirty_bitmap, 0, n);
-
for (i = 0; !is_dirty && i < n/sizeof(long); i++)
is_dirty = memslot->dirty_bitmap[i];
/* If nothing is dirty, don't bother messing with page tables. */
if (is_dirty) {
struct kvm_memslots *slots, *old_slots;
+ unsigned long *dirty_bitmap;
spin_lock(&kvm->mmu_lock);
kvm_mmu_slot_remove_write_access(kvm, log->slot);
spin_unlock(&kvm->mmu_lock);
- slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
- if (!slots)
- goto out_free;
+ r = -ENOMEM;
+ dirty_bitmap = vmalloc(n);
+ if (!dirty_bitmap)
+ goto out;
+ memset(dirty_bitmap, 0, n);
+ r = -ENOMEM;
+ slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
+ if (!slots) {
+ vfree(dirty_bitmap);
+ goto out;
+ }
memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
slots->memslots[log->slot].dirty_bitmap = dirty_bitmap;
@@ -2788,13 +2790,20 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
synchronize_srcu_expedited(&kvm->srcu);
dirty_bitmap = old_slots->memslots[log->slot].dirty_bitmap;
kfree(old_slots);
+
+ r = -EFAULT;
+ if (copy_to_user(log->dirty_bitmap, dirty_bitmap, n)) {
+ vfree(dirty_bitmap);
+ goto out;
+ }
+ vfree(dirty_bitmap);
+ } else {
+ r = -EFAULT;
+ if (clear_user(log->dirty_bitmap, n))
+ goto out;
}
r = 0;
- if (copy_to_user(log->dirty_bitmap, dirty_bitmap, n))
- r = -EFAULT;
-out_free:
- vfree(dirty_bitmap);
out:
mutex_unlock(&kvm->slots_lock);
return r;
--
To unsubscribe from this list: send the line "unsubscribe kvm-commits" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
