factor common code out of vm_page_alloc*contig_domain

[dougm]

Summary

Besides reducing code duplication, for the object case this avoids needlessly executing some code when a reservation is broken to release pages.

[dougm]

This change does slightly reduce the code size:
dougm@108-254-203-204:GENERIC $ size orig.vm_page.o

 text    data     bss     dec       hex   filename
50782   25808   13424   90014   0x15f9e   orig.vm_page.o

dougm@108-254-203-204:GENERIC $ size vm_page.o

 text    data     bss     dec       hex   filename
50670   25808   13424   89902   0x15f2e   vm_page.o

[kib]

sys/vm/vm_page.c

2195

This partial sentence should be reformulated now, I believe. Out of old context it is not sufficient, and should be a normal sentence.

2208

Now in vm_page_alloc_contig_domain(), this would loop without retrying vm_reserv_alloc_contig(). Was it intended? From the commit message it seems so, but vm_domain_alloc_fail() drops object lock which might change the disposition for reservations?

[dougm]

Improve comments.

[dougm]

sys/vm/vm_page.c

2208

It was intended. Now, if vm_reserv_reclaim_contig returns true, control goes to vm_reserv_object && vm_reserv_alloc_contig without a call to vm_domain_alloc_fail, so the object lock would not have been dropped, and the vm_reserv_alloc_contig call will fail a second time.