Make MAXPHYS tunable. Bump MAXPHYS to 1M.

Replace MAXPHYS by runtime variable maxphys. It is initialized from
MAXPHYS by default, but can be also adjusted with the tunable kern.maxphys.

Make b_pages[] array in struct buf flexible.  Size b_pages[] for buffer
cache buffers exactly to atop(maxbcachebuf) (currently it is sized to
atop(MAXPHYS)), and b_pages[] for pbufs is sized to atop(maxphys) + 1.
The +1 for pbufs allow several pbuf consumers, among them vmapbuf(),
to use unaligned buffers still sized to maxphys, esp. when such
buffers come from userspace (*).  Overall, we save significant amount
of otherwise wasted memory in b_pages[] for buffer cache buffers,
while bumping MAXPHYS to desired high value.

Eliminate all direct uses of the MAXPHYS constant in kernel and driver
sources, except a place which initialize maxphys.  Some random (and
arguably weird) uses of MAXPHYS, e.g. in linuxolator, are converted
straight.  Some drivers, which use MAXPHYS to size embeded structures,
get private MAXPHYS-like constant; their convertion is out of scope
for this work.

Changes to cam/, dev/ahci, dev/ata, dev/mpr, dev/mpt, dev/mvs,
dev/siis, where either submitted by, or based on changes by mav.

Suggested by: mav (*)
Reviewed by:	imp, mav, imp, mckusick, scottl (intermediate versions)
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
Differential revision:	https://reviews.freebsd.org/D27225

1 files changed, 3 insertions, 3 deletions

diff --git a/sys/geom/geom_dev.c b/sys/geom/geom_dev.c
index 3dcf8a38a1e2..9c33ab71e6c8 100644
--- a/sys/geom/geom_dev.c
+++ b/sys/geom/geom_dev.c
@@ -377,7 +377,7 @@ g_dev_taste(struct g_class *mp, struct g_provider *pp, int insist __unused)
 	}
 	dev = sc->sc_dev;
 	dev->si_flags |= SI_UNMAPPED;
-	dev->si_iosize_max = MAXPHYS;
+	dev->si_iosize_max = maxphys;
 	error = init_dumpdev(dev);
 	if (error != 0)
 		printf("%s: init_dumpdev() failed (gp->name=%s, error=%d)\n",
@@ -713,14 +713,14 @@ g_dev_ioctl(struct cdev *dev, u_long cmd, caddr_t data, int fflag, struct thread
 
 		if (zone_args->zone_cmd == DISK_ZONE_REPORT_ZONES) {
 			rep = &zone_args->zone_params.report;
-#define	MAXENTRIES	(MAXPHYS / sizeof(struct disk_zone_rep_entry))
+#define	MAXENTRIES	(maxphys / sizeof(struct disk_zone_rep_entry))
 			if (rep->entries_allocated > MAXENTRIES)
 				rep->entries_allocated = MAXENTRIES;
 			alloc_size = rep->entries_allocated *
 			    sizeof(struct disk_zone_rep_entry);
 			if (alloc_size != 0)
 				new_entries = g_malloc(alloc_size,
-				    M_WAITOK| M_ZERO);
+				    M_WAITOK | M_ZERO);
 			old_entries = rep->entries;
 			rep->entries = new_entries;
 		}