alloc memory from reservation before breaking it

[dougm]

Summary

vm_reserv_reclaim_contig breaks a reservation with enough free space to satisfy an allocation request and returns the free space to the buddy allocator. Change the function to allocate the request memory from the reservation before breaking it, and returning that memory to the caller. That avoids a second call to the buddy allocator and guarantees successful allocation after breaking the reservation, where that success is not currently guaranteed.

[alc]

sys/vm/vm_page.c

2200

This has to move. If "reclaim" succeeds, you don't want to do this.

[dougm]

Correct page accounting problem.

[alc]

sys/vm/vm_page.c

2205–2208

The indentation looks wrong.

2229–2231

As an aside, I find this KASSERT confusing because we disallow VM_ALLOC_WAITOK in the very first KASSERT.

2246

As an aside, I don't see the point of this loop because because we disallow VM_ALLOC_WAITOK in the very first KASSERT. Kostik? Mark?

sys/vm/vm_reserv.c

1390–1397

This could all be performed after the reservation is unlocked.

1402

This can be done before marking the pages as allocated.

[dougm]

Fix indentation. Move some code out of the scope of locks, as suggested.