Signed-off-by: Chenyi Qiang<chenyi.qi...@intel.com>
<...>
+
+int ram_block_attribute_realize(RamBlockAttribute *attr, MemoryRegion
*mr)
+{
+ uint64_t shared_bitmap_size;
+ const int block_size = qemu_real_host_page_size();
+ int ret;
+
+ shared_bitmap_size = ROUND_UP(mr->size, block_size) / block_size;
+
+ attr->mr = mr;
+ ret = memory_region_set_generic_state_manager(mr,
GENERIC_STATE_MANAGER(attr));
+ if (ret) {
+ return ret;
+ }
+ attr->shared_bitmap_size = shared_bitmap_size;
+ attr->shared_bitmap = bitmap_new(shared_bitmap_size);
Above introduces a bitmap to track the private/shared state of each 4KB
page. While functional, for large RAM blocks managed by guest_memfd,
this could lead to significant memory consumption.
Have you considered an alternative like a Maple Tree or a generic
interval tree? Both are often more memory-efficient for tracking ranges
of contiguous states.
Maybe not necessary. The memory overhead is 1 bit per page
(1/(4096*8)=0.003%). I think it is not too much.
It's certainly not optimal.
IIRC, QEMU already maintains 3 dirty bitmaps in
ram_list.dirty_memory (DIRTY_MEMORY_NUM = 3) for guest ram.
With KVM, we also allocate yet another dirty bitmap without
KVM_MEM_LOG_DIRTY_PAGES.
Assuming a 4 TiB VM, a single bitmap should be 128 MiB.
--
Cheers,
David / dhildenb
