K 10
svn:author
V 3
alc
K 8
svn:date
V 27
2018-07-19T17:01:10.527412Z
K 7
svn:log
V 1011
Revert r329254.  The underlying cause for the copy-on-write problem in
multithreaded programs that was addressed by r329254 was in the
implementation of pmap_enter() on some architectures, notably, amd64.
kib@, markj@ and I have audited all of the pmap_enter() implementations,
and fixed the broken ones, specifically, amd64 (r335784, r335971), i386
(r336092), mips (r336248), and riscv (r336294).

To be clear, the reason to address the problem within pmap_enter() and
revert r329254 is not just a matter of principle.  An effect of r329254
was that a copy-on-write fault actually entailed two page faults, not
one, even for single-threaded programs.  Now, in the expected case for
either single- or multithreaded programs, we are back to a single page
fault to complete a copy-on-write operation.  (In extremely rare
circumstances, a multithreaded program could suffer two page faults.)

Reviewed by:	kib, markj
Tested by:	truckman
MFC after:	3 weeks
Differential Revision:	https://reviews.freebsd.org/D16301

END