46 lines
1.9 KiB
Diff
46 lines
1.9 KiB
Diff
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From b50b9a0e2e5e8262c830df5994f3abbe0a37655a Mon Sep 17 00:00:00 2001
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From: Keqian Zhu <zhukeqian1@huawei.com>
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Date: Thu, 17 Dec 2020 09:49:40 +0800
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Subject: [PATCH] accel: kvm: Fix memory waste under mismatch page size
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When handle dirty log, we face qemu_real_host_page_size and
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TARGET_PAGE_SIZE. The first one is the granule of KVM dirty
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bitmap, and the second one is the granule of QEMU dirty bitmap.
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As qemu_real_host_page_size >= TARGET_PAGE_SIZE (kvm_init()
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enforced it), misuse TARGET_PAGE_SIZE to init kvmslot dirty_bmap
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may waste memory. For example, when qemu_real_host_page_size is
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64K and TARGET_PAGE_SIZE is 4K, it wastes 93.75% (15/16) memory.
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Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
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Reviewed-by: Andrew Jones <drjones@redhat.com>
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Reviewed-by: Peter Xu <peterx@redhat.com>
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Message-Id: <20201217014941.22872-2-zhukeqian1@huawei.com>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
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---
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accel/kvm/kvm-all.c | 6 +++++-
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1 file changed, 5 insertions(+), 1 deletion(-)
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diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
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index 5a6b89cc2a..4daff563a0 100644
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--- a/accel/kvm/kvm-all.c
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+++ b/accel/kvm/kvm-all.c
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@@ -551,8 +551,12 @@ static void kvm_memslot_init_dirty_bitmap(KVMSlot *mem)
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* too, in most cases).
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* So for now, let's align to 64 instead of HOST_LONG_BITS here, in
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* a hope that sizeof(long) won't become >8 any time soon.
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+ *
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+ * Note: the granule of kvm dirty log is qemu_real_host_page_size.
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+ * And mem->memory_size is aligned to it (otherwise this mem can't
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+ * be registered to KVM).
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*/
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- hwaddr bitmap_size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS),
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+ hwaddr bitmap_size = ALIGN(mem->memory_size / qemu_real_host_page_size,
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/*HOST_LONG_BITS*/ 64) / 8;
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mem->dirty_bmap = g_malloc0(bitmap_size);
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}
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--
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2.27.0
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