[PATCH 3/4] KVM: count the number of dirty pages for each memslot

[Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>]

This patch introduces the counter to hold the number of dirty pages in each
memslot. This eliminate the need to scan dirty bitmap for get_dirty_log.

We will also use this to optimize dirty logging later.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>
---
 arch/x86/kvm/x86.c       |    9 +++------
 include/linux/kvm_host.h |    1 +
 virt/kvm/kvm_main.c      |    6 +++++-
 3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 410d2d1..e9cf381 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3199,10 +3199,9 @@ static int kvm_vm_ioctl_reinject(struct kvm *kvm,
 int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 				      struct kvm_dirty_log *log)
 {
-	int r, i;
+	int r;
 	struct kvm_memory_slot *memslot;
 	unsigned long n;
-	unsigned long is_dirty = 0;
 
 	mutex_lock(&kvm->slots_lock);
 
@@ -3217,11 +3216,8 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 
 	n = kvm_dirty_bitmap_bytes(memslot);
 
-	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) {
+	if (memslot->nr_dirty_pages) {
 		struct kvm_memslots *slots, *old_slots;
 		unsigned long *dirty_bitmap;
 
@@ -3236,6 +3232,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
 			goto out;
 		memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
 		slots->memslots[log->slot].dirty_bitmap = dirty_bitmap;
+		slots->memslots[log->slot].nr_dirty_pages = 0;
 		slots->generation++;
 
 		old_slots = kvm->memslots;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 4bd663d..ce101b1 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -152,6 +152,7 @@ struct kvm_memory_slot {
 	unsigned long *rmap;
 	unsigned long *dirty_bitmap;
 	unsigned long *dirty_bitmap_head;
+	unsigned long nr_dirty_pages;
 	struct {
 		unsigned long rmap_pde;
 		int write_count;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fb93ff9..e1022ad 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -565,6 +565,7 @@ static int kvm_create_dirty_bitmap(struct kvm_memory_slot *memslot)
 		return -ENOMEM;
 
 	memslot->dirty_bitmap_head = memslot->dirty_bitmap;
+	memslot->nr_dirty_pages = 0;
 	return 0;
 }
 
@@ -1388,7 +1389,10 @@ void mark_page_dirty_in_slot(struct kvm *kvm, struct kvm_memory_slot *memslot,
 	if (memslot && memslot->dirty_bitmap) {
 		unsigned long rel_gfn = gfn - memslot->base_gfn;
 
-		generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
+		if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap)) {
+			generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
+			memslot->nr_dirty_pages++;
+		}
 	}
 }
 
-- 
1.7.1

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