Mapping shared guest memory page by page queried the address space
three times for every 16 KiB page: twice to find the placeholder the
page splits from, and once more to see whether the section page still
had to be committed, which it then committed on its own. For a range of
fresh direct memory that is seven system calls a page, and with shared
imports attached every direct mapping takes this path on the guest
thread that maps it, under the mapping lock.
A mapping that goes page by page now commits its section range once
through one window, and splits each page off the placeholder the
previous page left, whose extent it already knows; only a page after a
resident run or a demotion looks the placeholder up again. A page now
costs a placeholder split, the view and its protection.
Tested: built; windows_write_watch gains a case that maps 256 shared
pages and counts the address-space queries the mapping makes, then
stores to and reads back every page. With the per-page lookups it fails
(775 queries for 256 pages) and with this change it passes.
agc_driver_committed_imports, agc_write_watch_coverage,
agc_private_collect, agc_write_guards, agc_driver_dcc_keys_first_write,
agc_driver_residency_dirty_mirrors, agc_driver_residency_driver,
guest_memory and the host import, window import and alias store tests
pass.
WindowsMappings keys each physical page's state (moved into the section,
saved bytes of an unmapped resident page) by the section handle value.
sceKernelReleaseDirectMemory frees the backing before it unmaps the views,
so ForgetSection ran while those views still existed and kept their slots.
After the views went, the slots stayed under a handle value that Windows
hands out again, and the next direct allocation whose section got that
value started with the old page state: its first mapping went to the
section instead of private memory, or received the old allocation's bytes.
Views now share ownership of their slot, ForgetSection drops every slot
of the section at once, and JIT shared memory forgets its section before
closing it too.
fablevoid