[PATCH 8/8] KVM: MMU: Avoid handling same rmap_pde in kvm_handle_hva_range()

[Takuya Yoshikawa]

When we invalidate a THP page, we call the handler with the same
rmap_pde argument 512 times in the following loop:

  for each guest page in the range
    for each level
      unmap using rmap

This patch avoids these extra handler calls by changing the loop order
like this:

  for each level
    for each rmap in the range
      unmap using rmap

With the preceding patches in the patch series, this made THP page
invalidation more than 5 times faster on our x86 host: the host became
more responsive during swapping the guest's memory as a result.

Signed-off-by: Takuya Yoshikawa <yoshikawa.tak...@oss.ntt.co.jp>
---
 arch/x86/kvm/mmu.c |   28 ++++++++++++++++++----------
 1 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 3082199..d07b4ad 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1201,7 +1201,7 @@ static int kvm_handle_hva_range(struct kvm *kvm,
 
        kvm_for_each_memslot(memslot, slots) {
                unsigned long hva_start, hva_end;
-               gfn_t gfn, gfn_end;
+               gfn_t gfn_start, gfn_end;
 
                hva_start = max(start, memslot->userspace_addr);
                hva_end = min(end, memslot->userspace_addr +
@@ -1210,19 +1210,27 @@ static int kvm_handle_hva_range(struct kvm *kvm,
                        continue;
                /*
                 * {gfn(page) | page intersects with [hva_start, hva_end)} =
-                * {gfn, gfn+1, ..., gfn_end-1}.
+                * {gfn_start, gfn_start+1, ..., gfn_end-1}.
                 */
-               gfn = hva_to_gfn_memslot(hva_start, memslot);
+               gfn_start = hva_to_gfn_memslot(hva_start, memslot);
                gfn_end = hva_to_gfn_memslot(hva_end + PAGE_SIZE - 1, memslot);
 
-               for (; gfn < gfn_end; ++gfn) {
-                       for (j = PT_PAGE_TABLE_LEVEL;
-                            j < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++j) {
-                               unsigned long *rmapp;
+               for (j = PT_PAGE_TABLE_LEVEL;
+                    j < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++j) {
+                       unsigned long idx, idx_end;
+                       unsigned long *rmapp;
 
-                               rmapp = __gfn_to_rmap(gfn, j, memslot);
-                               ret |= handler(kvm, rmapp, memslot, data);
-                       }
+                       /*
+                        * {idx(page_j) | page_j intersects with
+                        *  [hva_start, hva_end)} = {idx, idx+1, ..., idx_end}.
+                        */
+                       idx = gfn_to_index(gfn_start, memslot->base_gfn, j);
+                       idx_end = gfn_to_index(gfn_end - 1, memslot->base_gfn, 
j);
+
+                       rmapp = __gfn_to_rmap(gfn_start, j, memslot);
+
+                       for (; idx <= idx_end; ++idx)
+                               ret |= handler(kvm, rmapp++, memslot, data);
                }
        }
 
-- 
1.7.5.4

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