phys_alloc_seg_contig: don't allocate past seg->end

[dougm]

Summary

In vm_phys_alloc_seg_contig, check alignment before checking orders of multiple memory blocks, to avoid such deeply nested code. In checking multiple memory blocks, check seg->end only once, against pa_end because there's no need to repeat the test for consecutive values of pa, and because the current code, in the case that pa reaches pa_end and passes seg->end in the same iteration, proceeds to allocate that memory.

[dougm]

Undo change involving fictitious seg.

[dougm]

Remove some offensive parts.

[dougm]

Update, rearrange comments.

[alc]

sys/vm/vm_phys.c

1456

insert a blank before the block comment

1462

pa += 1 << (PAGE_SHIFT + VM_NFREEORDER - 1);

then you are shifting by a constant and the compiler will warn if overflow occurs

1463

oind -> VM_NFREEORDER - 1

1465–1466

put this inside the loop

[dougm]

Accept all proffered advice.