MFC: r264565

MFC: r264565

Do not set M_BESTFIT if a strategy has already been provided.  This
fixes problems when using M_FIRSTFIT.

MFC: r280805

Add four new DDB commands to display vmem(9) statistics.

In particular, such DDB commands were added:
        show vmem <addr>
        show all vmem
        show vmemdump <addr>
        show all vmemdump

As possible usage, that allows to see KVA usage and fragmentation.

Approved by:	re (gjb)

git-svn-id: svn://svn.freebsd.org/base/stable/10@295870 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f