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Subject[PATCH 6/6] KVM: MMU: Avoid handling same rmap_pde in kvm_handle_hva_range()
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.

Note: in the new code we could not use trace_kvm_age_page(), so we just
dropped the point from kvm_handle_hva_range().

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
---
arch/x86/kvm/mmu.c | 37 +++++++++++++++++++------------------
1 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 477b3da..524f7c0 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1192,8 +1192,7 @@ static int kvm_handle_hva_range(struct kvm *kvm,
unsigned long data))
{
int j;
- int ret;
- int retval = 0;
+ int ret = 0;
struct kvm_memslots *slots;
struct kvm_memory_slot *memslot;

@@ -1201,7 +1200,7 @@ 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 +
@@ -1210,29 +1209,31 @@ 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) {
- ret = 0;
+ for (j = PT_PAGE_TABLE_LEVEL;
+ j < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++j) {
+ unsigned long idx, idx_end;
+ unsigned long *rmapp;

- for (j = PT_PAGE_TABLE_LEVEL;
- j < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++j) {
- unsigned long *rmapp;
+ /*
+ * {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, j, memslot);
- ret |= handler(kvm, rmapp, data);
- }
- trace_kvm_age_page(memslot->userspace_addr +
- (gfn - memslot->base_gfn) * PAGE_SIZE,
- memslot, ret);
- retval |= ret;
+ rmapp = __gfn_to_rmap(gfn_start, j, memslot);
+
+ for (; idx <= idx_end; ++idx)
+ ret |= handler(kvm, rmapp++, data);
}
}

- return retval;
+ return ret;
}

static int kvm_handle_hva(struct kvm *kvm, unsigned long hva,
--
1.7.5.4


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