K 10
svn:author
V 3
kib
K 8
svn:date
V 27
2018-08-13T16:48:46.990898Z
K 7
svn:log
V 705
Prevent some parallel swap-ins, rate-limit swapper swap-ins.

If faultin() was called outside swapper (from PHOLD()), do not allow
swapper to initiate additional swap-ins.  Swapper' initiated swap-ins
are serialized because they are synchronous and executed in the
context of the thread0.  With the added limitation, we only allow
parallel swap-ins from PHOLD(), which is up to PHOLD() users to
manage, usually they do not need to.

Rate-limit swapper' swap-ins to one in the MAXSLP / 2 seconds
interval, counting faultin() swapins.

Suggested by:	alc
Reviewed by:	alc, markj
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Differential revision:	https://reviews.freebsd.org/D16610

END