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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
TARGET_PAGE_SIZE. The first one is the granule of KVM dirty
bitmap, and the second one is the granule of QEMU dirty bitmap.

As qemu_real_host_page_size >= TARGET_PAGE_SIZE (kvm_init()
enforced it), misuse TARGET_PAGE_SIZE to init kvmslot dirty_bmap
may waste memory. For example, when qemu_real_host_page_size is
64K and TARGET_PAGE_SIZE is 4K, it wastes 93.75% (15/16) memory.

Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20201217014941.22872-2-zhukeqian1@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
This commit is contained in:
Chen Qun 2020-12-17 09:49:40 +08:00
parent 0412463a76
commit 77ac49a900
1 changed files with 45 additions and 0 deletions
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45
accel-kvm-Fix-memory-waste-under-mismatch-page-size.patch Normal file
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@ -0,0 +1,45 @@
From b50b9a0e2e5e8262c830df5994f3abbe0a37655a Mon Sep 17 00:00:00 2001
From: Keqian Zhu <zhukeqian1@huawei.com>
Date: Thu, 17 Dec 2020 09:49:40 +0800
Subject: [PATCH] accel: kvm: Fix memory waste under mismatch page size
When handle dirty log, we face qemu_real_host_page_size and
TARGET_PAGE_SIZE. The first one is the granule of KVM dirty
bitmap, and the second one is the granule of QEMU dirty bitmap.
As qemu_real_host_page_size >= TARGET_PAGE_SIZE (kvm_init()
enforced it), misuse TARGET_PAGE_SIZE to init kvmslot dirty_bmap
may waste memory. For example, when qemu_real_host_page_size is
64K and TARGET_PAGE_SIZE is 4K, it wastes 93.75% (15/16) memory.
Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20201217014941.22872-2-zhukeqian1@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
---
accel/kvm/kvm-all.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 5a6b89cc2a..4daff563a0 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -551,8 +551,12 @@ static void kvm_memslot_init_dirty_bitmap(KVMSlot *mem)
* too, in most cases).
* So for now, let's align to 64 instead of HOST_LONG_BITS here, in
* a hope that sizeof(long) won't become >8 any time soon.
+ *
+ * Note: the granule of kvm dirty log is qemu_real_host_page_size.
+ * And mem->memory_size is aligned to it (otherwise this mem can't
+ * be registered to KVM).
*/
- hwaddr bitmap_size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS),
+ hwaddr bitmap_size = ALIGN(mem->memory_size / qemu_real_host_page_size,
/*HOST_LONG_BITS*/ 64) / 8;
mem->dirty_bmap = g_malloc0(bitmap_size);
}
--
2.27.0