vm_reserv: introduce unmanaged reservations

[bnovkov]

Summary

This is the first of four patches in a series that aims to replace uma_small_alloc with a reservation-aware 0-order page allocator.

This patch introduces unmanaged reservations, i.e. reservations that are not a part of any vm_object but are still used to serve page allocation requests. In this case, they are used to allocate 0-order pages for UMA zones.

[kib]

sys/vm/vm_reserv.c

151

Why 4 bits and not 1?

Or you might use a special invalid object value like (vm_object_t)1 instead of adding inpartpopq flags. I mention this because the check for free reservation is rv->object == NULL, which can be kept intact this way. Also unmanaged becomes exclusive with managed reservation condition by the mere way it is stored.

[bnovkov]

sys/vm/vm_reserv.c

151

No particular reason, the 4 bit split seemed cleaner since both fields are effectively booleans.

I hadn't considered the special vm_object approach, I like it more than the current approach of adding in new fields.
I'll try to work it into the patch.

[bnovkov]

Address @kib 's comment - unmanaged reservations are now distinguished using an invalid vm_object value instead of a separate variable.

[kib]

sys/vm/vm_reserv.c

1469

you can express the 4 lines above as

return (rv->object == VM_RESERV_NOOBJ_MARK);