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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>
master
Keqian Zhu 2020-12-17 09:49:40 +08:00 committed by Paolo Bonzini
parent 10b6ee1616
commit e0a8f99355
1 changed files with 5 additions and 1 deletions
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6
accel/kvm/kvm-all.c
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@ -598,8 +598,12 @@ 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);
}