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authorTakuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>2010-10-27 18:23:54 +0900
committerAvi Kivity <avi@redhat.com>2011-01-12 11:28:46 +0200
commit515a01279a187415322a80736800a7d6325876ab (patch)
tree8690a1b26013cb385b9d143c83301bdab758dd48
parenta36a57b1a19bce17b67f5c6f43460baf664ae5fa (diff)
downloadlinux-515a01279a187415322a80736800a7d6325876ab.tar.gz
KVM: pre-allocate one more dirty bitmap to avoid vmalloc()
Currently x86's kvm_vm_ioctl_get_dirty_log() needs to allocate a bitmap by vmalloc() which will be used in the next logging and this has been causing bad effect to VGA and live-migration: vmalloc() consumes extra systime, triggers tlb flush, etc. This patch resolves this issue by pre-allocating one more bitmap and switching between two bitmaps during dirty logging. Performance improvement: I measured performance for the case of VGA update by trace-cmd. The result was 1.5 times faster than the original one. In the case of live migration, the improvement ratio depends on the workload and the guest memory size. In general, the larger the memory size is the more benefits we get. Note: This does not change other architectures's logic but the allocation size becomes twice. This will increase the actual memory consumption only when the new size changes the number of pages allocated by vmalloc(). Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp> Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
-rw-r--r--arch/x86/kvm/x86.c16
-rw-r--r--include/linux/kvm_host.h1
-rw-r--r--virt/kvm/kvm_main.c11
3 files changed, 15 insertions, 13 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a2a78547243..35f82f2c66f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3208,18 +3208,15 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
struct kvm_memslots *slots, *old_slots;
unsigned long *dirty_bitmap;
- r = -ENOMEM;
- dirty_bitmap = vmalloc(n);
- if (!dirty_bitmap)
- goto out;
+ dirty_bitmap = memslot->dirty_bitmap_head;
+ if (memslot->dirty_bitmap == dirty_bitmap)
+ dirty_bitmap += n / sizeof(long);
memset(dirty_bitmap, 0, n);
r = -ENOMEM;
slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
- if (!slots) {
- vfree(dirty_bitmap);
+ if (!slots)
goto out;
- }
memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
slots->memslots[log->slot].dirty_bitmap = dirty_bitmap;
slots->generation++;
@@ -3235,11 +3232,8 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
spin_unlock(&kvm->mmu_lock);
r = -EFAULT;
- if (copy_to_user(log->dirty_bitmap, dirty_bitmap, n)) {
- vfree(dirty_bitmap);
+ if (copy_to_user(log->dirty_bitmap, dirty_bitmap, n))
goto out;
- }
- vfree(dirty_bitmap);
} 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 462b982fedf..bcf71c7730f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -150,6 +150,7 @@ struct kvm_memory_slot {
unsigned long flags;
unsigned long *rmap;
unsigned long *dirty_bitmap;
+ unsigned long *dirty_bitmap_head;
struct {
unsigned long rmap_pde;
int write_count;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 0021c286214..27649fdaa00 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -449,8 +449,9 @@ static void kvm_destroy_dirty_bitmap(struct kvm_memory_slot *memslot)
if (!memslot->dirty_bitmap)
return;
- vfree(memslot->dirty_bitmap);
+ vfree(memslot->dirty_bitmap_head);
memslot->dirty_bitmap = NULL;
+ memslot->dirty_bitmap_head = NULL;
}
/*
@@ -537,15 +538,21 @@ static int kvm_vm_release(struct inode *inode, struct file *filp)
return 0;
}
+/*
+ * Allocation size is twice as large as the actual dirty bitmap size.
+ * This makes it possible to do double buffering: see x86's
+ * kvm_vm_ioctl_get_dirty_log().
+ */
static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot)
{
- unsigned long dirty_bytes = kvm_dirty_bitmap_bytes(memslot);
+ unsigned long dirty_bytes = 2 * kvm_dirty_bitmap_bytes(memslot);
memslot->dirty_bitmap = vmalloc(dirty_bytes);
if (!memslot->dirty_bitmap)
return -ENOMEM;
memset(memslot->dirty_bitmap, 0, dirty_bytes);
+ memslot->dirty_bitmap_head = memslot->dirty_bitmap;
return 0;
}