vm_map: overlap system map mutex and user man sx

[kib]

Summary

This saves 616-584 = 32 bytes per struct vmspace on amd64, which allows
to pack 7 vmspaces per page vs. 6 for non-overlapping layout.

I used anonymous union member feature to avoid too much churn.

[markj]

My comments are just suggestions.

sys/vm/vm_map.c

296

Maybe explicitly set map->system_map = false here, just for clarity.

sys/vm/vm_map.h

214

Should we change the system_map type to bool?

488–489

As a matter of style, I'd prefer a separate vm_map_init_system() rather than having a naked boolean parameter.

[kib]

sys/vm/vm_map.c

296

I added a comment to memset() above. IMO assigning the field twice is not needed. More, I would ask myself question why this is done.

sys/vm/vm_map.h

214

I consider moving it to flag in the next proposed change. In fact, lets add it to this review.

[kib]

Add wrapper map_is_system_map().
Convert system_map and needs_wakeup to flags.

[alc]

sys/vm/vm_map.h

78

Do we still use this?

282

vm_map_is_system() would be, IMHO, more stylistically consistent, and 1 character shorter. :-) Otherwise, I'm supportive of this change.

[kib]

vm_map_is_system()
Remove vm_flags_t
Some updates to vm_map(9)