Optimize memory handling (#1963)

* optimize ram block handling

Save the last element of the ram_list. This allows to
faster find where to add new elements when they are not
bigger then page size.

* save ram_list freed

this keeps the optimization for find_ram_offset() intact after snapshot
restore.

* cow only clear the tlb of affected pages

* update flatview when possible

Building each flatview new when the memory has changed is quite
expensive when many MemoryRegions are used. This is an issue when using
snapshots.

* update benchmark for new api

* save flatview in context

this avoids rebuilding the flatview when restore a context.

* init context flatview with zero

* address_space_dispatch_clear remove subpage with higher priority

* docutemnt the options for UC_CTL_CONTEXT_MODE

Specialy stress that with UC_CTL_CONTEXT_MEMORY it is not possible to
use the context with a different unicorn object.

qemu/include/exec/memory-internal.h

@@ -45,6 +45,7 @@ void flatview_add_to_dispatch(struct uc_struct *uc, FlatView *fv, MemoryRegionSe
 AddressSpaceDispatch *address_space_dispatch_new(struct uc_struct *uc, FlatView *fv);
 void address_space_dispatch_compact(AddressSpaceDispatch *d);
 void address_space_dispatch_free(AddressSpaceDispatch *d);
+void address_space_dispatch_clear(AddressSpaceDispatch *d);
 
 void mtree_print_dispatch(struct AddressSpaceDispatch *d,
                           MemoryRegion *root);

qemu/include/exec/memory.h

@@ -1220,5 +1220,6 @@ void memory_unmap(struct uc_struct *uc, MemoryRegion *mr);
 void memory_moveout(struct uc_struct *uc, MemoryRegion *mr);
 void memory_movein(struct uc_struct *uc, MemoryRegion *mr);
 int memory_free(struct uc_struct *uc);
+bool flatview_copy(struct uc_struct *uc, FlatView *dst, FlatView *src, bool update_dispatcher);
 
 #endif