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, 8 insertions, 7 deletions

diff --git a/sys/vm/vnode_pager.c b/sys/vm/vnode_pager.c
index 0c67a3785ea2..e75c6fb6b5d7 100644
--- a/sys/vm/vnode_pager.c
+++ b/sys/vm/vnode_pager.c
@@ -817,7 +817,7 @@ vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int count,
 
 	KASSERT(foff < object->un_pager.vnp.vnp_size,
 	    ("%s: page %p offset beyond vp %p size", __func__, m[0], vp));
-	KASSERT(count <= nitems(bp->b_pages),
+	KASSERT(count <= atop(maxphys),
 	    ("%s: requested %d pages", __func__, count));
 
 	/*
@@ -832,6 +832,7 @@ vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int count,
 	}
 
 	bp = uma_zalloc(vnode_pbuf_zone, M_WAITOK);
+	MPASS((bp->b_flags & B_MAXPHYS) != 0);
 
 	/*
 	 * Get the underlying device blocks for the file with VOP_BMAP().
@@ -916,10 +917,10 @@ vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int count,
 	 * Check that total amount of pages fit into buf.  Trim rbehind and
 	 * rahead evenly if not.
 	 */
-	if (rbehind + rahead + count > nitems(bp->b_pages)) {
+	if (rbehind + rahead + count > atop(maxphys)) {
 		int trim, sum;
 
-		trim = rbehind + rahead + count - nitems(bp->b_pages) + 1;
+		trim = rbehind + rahead + count - atop(maxphys) + 1;
 		sum = rbehind + rahead;
 		if (rbehind == before) {
 			/* Roundup rbehind trim to block size. */
@@ -930,9 +931,9 @@ vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int count,
 			rbehind -= trim * rbehind / sum;
 		rahead -= trim * rahead / sum;
 	}
-	KASSERT(rbehind + rahead + count <= nitems(bp->b_pages),
-	    ("%s: behind %d ahead %d count %d", __func__,
-	    rbehind, rahead, count));
+	KASSERT(rbehind + rahead + count <= atop(maxphys),
+	    ("%s: behind %d ahead %d count %d maxphys %lu", __func__,
+	    rbehind, rahead, count, maxphys));
 
 	/*
 	 * Fill in the bp->b_pages[] array with requested and optional   
@@ -1014,7 +1015,7 @@ vnode_pager_generic_getpages(struct vnode *vp, vm_page_t *m, int count,
 		*a_rahead = bp->b_pgafter;
 
 #ifdef INVARIANTS
-	KASSERT(bp->b_npages <= nitems(bp->b_pages),
+	KASSERT(bp->b_npages <= atop(maxphys),
 	    ("%s: buf %p overflowed", __func__, bp));
 	for (int j = 1, prev = 0; j < bp->b_npages; j++) {
 		if (bp->b_pages[j] == bogus_page)