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

[Takuya Yoshikawa]

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.tak...@oss.ntt.co.jp>
---
 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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