this change is in preparation for amd64. the systab calling
convention was also changed to return uintptr (as segattach
returns a pointer) and the arguments are now passed as
va_list which handles amd64 arguments properly (all arguments
are passed in 64bit quantities on the stack, tho the upper
part will not be initialized when the element is smaller
than 8 bytes).
this is partial. xalloc needs to be converted in the future.
the lock order of page.Lock -> palloc.hashlock was
violated in cachedel() which is called from the
pager. change the code to do it in the right oder
to prevent deadlock.
change lookpage to retry on false hit. i assume that
a false hit means:
a) we'r low on memory -> cached page got uncached/reused
b) duppage() got called on the page, meaning theres another
cached copy in the image now.
paging in is expensive compared to the hashtable lookup, so
i think retrying is better.
cleanup fixfault, adding comments.
