NFC: Cleanups only (mostly to comments).

Fix grammar, spelling, layout, and occasionally, content
of comments added in the previous commit, and even add one
or two new ones.

While here, some 80 column police action.

The only difference in the generated object files is the RCSID.
(On amd64 anyway).

Author: kre

sys/uvm/uvm_swap.c

@@ -1,4 +1,4 @@
-/*	$NetBSD: uvm_swap.c,v 1.214 2026/02/13 03:44:49 kre Exp $	*/
+/*	$NetBSD: uvm_swap.c,v 1.215 2026/02/13 19:16:41 kre Exp $	*/
 
 /*
  * Copyright (c) 1995, 1996, 1997, 2009 Matthew R. Green
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uvm_swap.c,v 1.214 2026/02/13 03:44:49 kre Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uvm_swap.c,v 1.215 2026/02/13 19:16:41 kre Exp $");
 
 #include "opt_uvmhist.h"
 #include "opt_compat_netbsd.h"
@@ -500,10 +500,11 @@ int (*uvm_swap_stats50)(const struct sys_swapctl_args *, register_t *) =
 
 /*
  * sys_swapctl: main entry point for swapctl(2) system call
- * 	[with two helper functions: swap_on and swap_off]
+ * 	[with three helper functions: swap_on, swap_off and uvm_swap_stats]
  */
 int
-sys_swapctl(struct lwp *l, const struct sys_swapctl_args *uap, register_t *retval)
+sys_swapctl(struct lwp *l, const struct sys_swapctl_args *uap,
+   register_t *retval)
 {
 	/* {
 		syscallarg(int) cmd;
@@ -782,7 +783,7 @@ uvm_swap_stats(char *ptr, int misc,
 	struct swapdev *sdp, **sdps, **sp;
 	struct swapent sep;
 	size_t sdpsize = 0;
-	struct swapdev *stackbuf[8];
+	struct swapdev *stackbuf[8];	/* magic 8, any number >1 will do */
 	int count, slots;
 	int error;
 
@@ -799,7 +800,7 @@ uvm_swap_stats(char *ptr, int misc,
 	KASSERT(rw_lock_held(&swap_syscall_lock));
 
 	/*
-	 * Allocate space for pointers to all swapdevs
+	 * Allocate space (slots) for pointers to all swapdevs
 	 *
 	 * This needs to be done here (not earlier) (and so needs
 	 * the unlock/lock dance) because of the way the various
@@ -820,16 +821,18 @@ uvm_swap_stats(char *ptr, int misc,
 		return E2BIG;
 
 	/*
-	 * One slot for each currently existing swap device,
-	 * but limited no more than the request wants (misc).
+	 * One slot for each currently existing swap device, but
+	 * limited (above) to no more than the request wants (misc).
+	 * Each slot needs space for a pointer to a swapdev.
 	 */
 	sdpsize = (size_t)slots * sizeof sdp;
 
 	/*
-	 * Borrow from kmem_tmpbuf_alloc() but don't use it
+	 * Borrow from kmem_tmpbuf_alloc(9) but don't use that
 	 * so we don't need to do the unlock dance unnecessarily
 	 */
 	if (sdpsize <= sizeof stackbuf) {
+		/* Should be the common case */
 		sdps = stackbuf;
 	} else {
 		rw_exit(&swap_syscall_lock);
@@ -841,48 +844,43 @@ uvm_swap_stats(char *ptr, int misc,
 		/*
 		 * At this point, 3 possibilities.
 		 *
-		 * uvmexp.nswapdev has increased, as a
-		 * new swap device got added.  That's OK,
-		 * just ignore the excess device, and
-		 * return the first N (the number that
-		 * were there when we started.
+		 * 1. uvmexp.nswapdev has increased.
 		 *
-		 * uvmexp.nswapdev has decreased, a swap
-		 * device was deleted.   In this case we
-		 * will return less devices than requested
-		 * but that's OK.  We will have more memory
-		 * than is needed to save them all, but
-		 * just a little more, and it gets freed
-		 * just below.
+		 * A new swap device got added.  That's OK, just ignore the
+		 * excess device(s), and return the first N (the number that
+		 * were there when we started).
 		 *
-		 * uvmexp.nswapdev hasn't changed.   This
-		 * will be the usual case (no swapctl operations
-		 * occurred while the lock was releases - or
-		 * possibly a device was deleted and another
-		 * added - that's irrelevant, at this point
-		 * all that matters is the number of devices,
-		 * we haven't looked at the lists yet.
+		 * 2. uvmexp.nswapdev has decreased.
 		 *
-		 * So we never need to repeat this allocation,
-		 * Once is quite enough.
+		 * A swap device was deleted.  In this case we will return
+		 * less devices than requested but that's OK.  We will have
+		 * more slot memory than is needed to save them all, but just
+		 * a little more, and it gets freed just below.
 		 *
-		 * And we never need to look at uvmexp.nswapdev
-		 * again!
+		 * 3. uvmexp.nswapdev hasn't changed.
+		 *
+		 * This will be the usual case; no swapctl operations occurred
+		 * while the lock was released, or possibly a device was
+		 * deleted and another added - that's irrelevant.  At this
+		 * point all that matters is the number of devices, we haven't
+		 * looked at the lists yet.
+		 *
+		 * So we never need to adjust this allocation.
+		 *
+		 * And we don't need to look at uvmexp.nswapdev again!
 		 */
 	}
 
 	KASSERT(rw_lock_held(&swap_syscall_lock));
 
 	/*
-	 * Collect all of the swap descriptors, while
-	 * holding the data lock, so the lists cannot
-	 * change.   Then they can be used safely.
+	 * Collect all of the swap descriptors, while holding the data lock,
+	 * so the lists cannot change.   Then they can be used safely.
 	 *
-	 * They cannot be deleted, because swap_syscall_lock
-	 * is held, but the lists holding them can be adjusted
-	 * except in this small loop where we lock out that
-	 * kind of activity.   No processing happens here,
-	 * this is fast, with no func calls, or anything which
+	 * Entries cannot be deleted, because swap_syscall_lock is held,
+	 * but the lists holding them can be reordered except in this small
+	 * loop where we lock out that kind of activity.   No processing
+	 * happens here, this is fast, with no func calls, or anything which
 	 * might perform operations which might need the lock.
 	 */
 	mutex_enter(&uvm_swap_data_lock);
@@ -893,11 +891,11 @@ uvm_swap_stats(char *ptr, int misc,
 			if (++count <= slots)
 				*sp++ = sdp;
 			/*
-			 * don't bother with exiting the loops
-			 * early, they tend to be very short,
-			 * and not exhausting them is a very rare
-			 * occurrence.  So just loop and do nothing
-			 * in the odd case we could break out early.
+			 * don't bother with exiting the loops early,
+			 * the lists tend to be very short, and not
+			 * exhausting them is a very rare occurrence.
+			 * So just loop and do nothing (but count) in
+			 * the odd case we could have broken out early.
 			 */
 		}
 	}
@@ -913,13 +911,16 @@ uvm_swap_stats(char *ptr, int misc,
 	if (misc > count)		/* the number of devices now */
 		misc = count;
 
+	/*
+	 * This is the actual work of uvm_swap_stats() - above was bookkeeping.
+	 */
 	error = 0;
 	count = 0;
 	sp = sdps;
 	while (misc-- > 0) {
 		int inuse;
 
-		sdp = *sp++;
+		sdp = *sp++;	/* The next swapdev, from the next slot */
 
 		inuse = btodb((uint64_t)sdp->swd_npginuse <<
 		    PAGE_SHIFT);
@@ -937,8 +938,8 @@ uvm_swap_stats(char *ptr, int misc,
    out:;
 	if (sdps != stackbuf) {
 		/*
-		 * XXX should unlock & lock again here
-		 * as well probably, but for now, no...
+		 * XXX should unlock & lock again here probably,
+		 *     but for now, no...
 		 */
 		kmem_free(sdps, sdpsize);
 	}
@@ -1062,7 +1063,7 @@ swap_on(struct lwp *l, struct swapdev *sdp)
 		goto bad;
 	}
 
-	UVMHIST_LOG(pdhist, "  dev=%#jx: size=%jd addr=%jd", dev, size, addr, 0);
+	UVMHIST_LOG(pdhist,"  dev=%#jx: size=%jd addr=%jd", dev, size, addr, 0);
 
 	/*
 	 * now we need to allocate an extent to manage this swap device
@@ -1181,7 +1182,8 @@ swap_off(struct lwp *l, struct swapdev *sdp)
 	int error = 0;
 
 	UVMHIST_FUNC(__func__);
-	UVMHIST_CALLARGS(pdhist, "  dev=%#jx, npages=%jd", sdp->swd_dev,npages, 0, 0);
+	UVMHIST_CALLARGS(pdhist,
+	    "  dev=%#jx, npages=%jd", sdp->swd_dev,npages, 0, 0);
 
 	KASSERT(rw_write_held(&swap_syscall_lock));
 	KASSERT(mutex_owned(&uvm_swap_data_lock));
@@ -1429,7 +1431,8 @@ static int
 swread(dev_t dev, struct uio *uio, int ioflag)
 {
 	UVMHIST_FUNC(__func__);
-	UVMHIST_CALLARGS(pdhist, "  dev=%#jx offset=%#jx", dev, uio->uio_offset, 0, 0);
+	UVMHIST_CALLARGS(pdhist,
+	    "  dev=%#jx offset=%#jx", dev, uio->uio_offset, 0, 0);
 
 	return (physio(swstrategy, NULL, dev, B_READ, minphys, uio));
 }
@@ -1442,7 +1445,8 @@ static int
 swwrite(dev_t dev, struct uio *uio, int ioflag)
 {
 	UVMHIST_FUNC(__func__);
-	UVMHIST_CALLARGS(pdhist, "  dev=%#jx offset=%#jx", dev, uio->uio_offset, 0, 0);
+	UVMHIST_CALLARGS(pdhist,
+	    "  dev=%#jx offset=%#jx", dev, uio->uio_offset, 0, 0);
 
 	return (physio(swstrategy, NULL, dev, B_WRITE, minphys, uio));
 }
@@ -1992,7 +1996,8 @@ uvm_swap_io(struct vm_page **pps, int startslot, int npages, int flags)
 	int	error, mapinflags;
 	bool write, async, swap_encrypt;
 	UVMHIST_FUNC(__func__);
-	UVMHIST_CALLARGS(pdhist, "<- called, startslot=%jd, npages=%jd, flags=%#jx",
+	UVMHIST_CALLARGS(pdhist,
+	    "<- called, startslot=%jd, npages=%jd, flags=%#jx",
 	    startslot, npages, flags, 0);
 
 	write = (flags & B_READ) == 0;