[PATCH 5/7] KVM: cache the last used slot

[Xiao Guangrong]

Cache the last used slot, the hit ratio is more than 35% during my test

Signed-off-by: Xiao Guangrong <xiaoguangr...@cn.fujitsu.com>
---
 include/linux/kvm_host.h |    1 +
 virt/kvm/kvm_main.c      |   11 +++++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f1963a4..7fbae16 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -225,6 +225,7 @@ struct kvm_memslots {
        int nmemslots;
        int used_slots;
        u64 generation;
+       struct kvm_memory_slot *slot_cache;
        struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
        struct kvm_memory_slot *slots_sort[KVM_MEM_SLOTS_NUM];
 };
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 0795426..4917d6a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -643,15 +643,21 @@ static struct kvm_memory_slot *search_memslots(struct 
kvm_memslots *slots,
                                               gfn_t gfn)
 {
        int start = 0, end = slots->used_slots, idx;
-       struct kvm_memory_slot *memslot;
+       struct kvm_memory_slot *memslot = slots->slot_cache;
+
+       if (memslot && gfn >= memslot->base_gfn &&
+             gfn < memslot->base_gfn + memslot->npages)
+               return memslot;
 
        while (start < end) {
                idx = (start + end) / 2;
                memslot = slots->slots_sort[idx];
 
                if (gfn >= memslot->base_gfn &&
-                     gfn < memslot->base_gfn + memslot->npages)
+                     gfn < memslot->base_gfn + memslot->npages) {
+                       slots->slot_cache = memslot;
                        return memslot;
+               }
 
                if (memslot->base_gfn < gfn)
                        start = idx + 1;
@@ -684,6 +690,7 @@ void memslots_updated(struct kvm_memslots *slots, int 
slot_id)
        if (slot_id >= slots->nmemslots)
                slots->nmemslots = slot_id + 1;
        slots->generation++;
+       slots->slot_cache = NULL;
        sort_memslots(slots);
 }
 
-- 
1.7.4

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