Reduce object locking in vm_fault. The object is only needed until we have an exclusive busy.

[jeff]

Summary

This drastically shortens maximum hold times on object locks in fault. We will basically only hold it through page allocation. It also eliminates some ugly lock/unlock/relock style code.

I intend to continue to refactor fault into smaller functions but I wanted to introduce the locking change first since it has the largest functional impact.

[jeff]

sys/vm/vm_fault.c

340

We could almost drop the lock before pmap_enter() but we are relying on it to prevent invalidation of pages for read-only faults.

633

I don't really like this but my only other option is to perhaps make this bool part of the fault_state.

962

Default objects hold the lock for the full duration.

1114

I don't like the extra label but I am continuing to break this function up and simplify control flow in later patches.

1210

Fixed indentation while adding the extra TRYWLOCK.

1462

This is actually a fairly substantial win.

[kib]

sys/vm/vm_fault.c

337

So we potentially dirty the object even despite the pmap_enter() could fail, same for prefault.

962

This explanation should be added to the comment, perhaps ?

1185

'A valid page has been found, busied by us' (modulo my english).

1210

And remove useless () around conditions while there, please.

[jeff]

sys/vm/vm_fault.c

337

Yeah it's safe to move this down. I can do so.

1185

A valid page has been found and exclusively busied.

1210

will do.

[jeff]

Review feedback. Mostly style and comments. Re-shuffle vm_fault_soft_fast() to properly handle the error case.