The page daemon always tries to build a 64K cluster of pages to
write to the swap partition.  When one of the many uvm_swap_io()
allocations fails and returns VM_PAGER_AGAIN, the pager layer,
re-try with a single page.

Since r2k22 there is a pre-allocated 64K cluster of pages in swap
layer.   If it is already used, the page daemon will wait for it
to be released by the aiodoned thread.

In fact this pre-allocated cluster and the sleep associated to it,
is what makes the page daemon release the KERNEL_LOCK() and allows
the aiodoned thread to release pages written to disk.  Without this
the page daemon enters an infinite loop holding the KERNEL_LOCK()
and never allows the aiodoned to release pages.

So I'd like to kill this dead code.  This is a step towards cleanup
the uvm_pager_* layer a requirement to clean the uvnode layer.

ok?

Index: uvm/uvm_pager.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pager.c,v
diff -u -p -r1.92 uvm_pager.c
--- uvm/uvm_pager.c	24 Jul 2024 12:18:10 -0000	1.92
+++ uvm/uvm_pager.c	8 Nov 2024 10:11:25 -0000
@@ -520,7 +520,6 @@ uvm_pager_put(struct uvm_object *uobj, s
 	 * now attempt the I/O.   if we have a failure and we are
 	 * clustered, we will drop the cluster and try again.
 	 */
-ReTry:
 	if (uobj) {
 		result = uobj->pgops->pgo_put(uobj, ppsp, *npages, flags);
 	} else {
@@ -564,48 +563,34 @@ ReTry:
 		 * "swblk" (for transient errors, so we can retry),
 		 * or 0 (for hard errors).
 		 */
-		if (uobj == NULL && pg != NULL) {
-			/* XXX daddr_t -> int */
-			int nswblk = (result == VM_PAGER_AGAIN) ? swblk : 0;
-			if (pg->pg_flags & PQ_ANON) {
-				rw_enter(pg->uanon->an_lock, RW_WRITE);
-				pg->uanon->an_swslot = nswblk;
-				rw_exit(pg->uanon->an_lock);
-			} else {
-				rw_enter(pg->uobject->vmobjlock, RW_WRITE);
-				uao_set_swslot(pg->uobject,
-					       pg->offset >> PAGE_SHIFT,
-					       nswblk);
-				rw_exit(pg->uobject->vmobjlock);
-			}
-		}
-		if (result == VM_PAGER_AGAIN) {
-			/*
-			 * for transient failures, free all the swslots that
-			 * we're not going to retry with.
-			 */
-			if (uobj == NULL) {
-				if (pg) {
-					/* XXX daddr_t -> int */
-					uvm_swap_free(swblk + 1, *npages - 1);
+		if (uobj == NULL) {
+			if (pg != NULL) {
+				if (pg->pg_flags & PQ_ANON) {
+					rw_enter(pg->uanon->an_lock, RW_WRITE);
+					pg->uanon->an_swslot = 0;
+					rw_exit(pg->uanon->an_lock);
 				} else {
-					/* XXX daddr_t -> int */
-					uvm_swap_free(swblk, *npages);
+					rw_enter(pg->uobject->vmobjlock, RW_WRITE);
+					uao_set_swslot(pg->uobject,
+					    pg->offset >> PAGE_SHIFT, 0);
+					rw_exit(pg->uobject->vmobjlock);
 				}
 			}
-			if (pg) {
-				ppsp[0] = pg;
-				*npages = 1;
-				goto ReTry;
-			}
-		} else if (uobj == NULL) {
 			/*
-			 * for hard errors on swap-backed pageouts,
-			 * mark the swslots as bad.  note that we do not
-			 * free swslots that we mark bad.
+			 * for transient failures, free all the swslots
 			 */
-			/* XXX daddr_t -> int */
-			uvm_swap_markbad(swblk, *npages);
+			if (result == VM_PAGER_AGAIN) {
+				/* XXX daddr_t -> int */
+				uvm_swap_free(swblk, *npages);
+			} else {
+				/*
+				 * for hard errors on swap-backed pageouts,
+				 * mark the swslots as bad.  note that we do not
+				 * free swslots that we mark bad.
+				 */
+				/* XXX daddr_t -> int */
+				uvm_swap_markbad(swblk, *npages);
+			}
 		}
 	}
 
@@ -614,7 +599,6 @@ ReTry:
 	 * was one).    give up!   the caller only has one page ("pg")
 	 * to worry about.
 	 */
-	
 	return result;
 }
 
Index: uvm/uvm_pdaemon.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pdaemon.c,v
diff -u -p -r1.129 uvm_pdaemon.c
--- uvm/uvm_pdaemon.c	7 Nov 2024 10:46:52 -0000	1.129
+++ uvm/uvm_pdaemon.c	8 Nov 2024 09:34:31 -0000
@@ -859,8 +859,6 @@ uvmpd_scan_inactive(struct uvm_pmalloc *
 					if (result != VM_PAGER_AGAIN)
 						uvm_pageactivate(p);
 					pmap_clear_reference(p);
-					/* XXXCDC: if (swap_backed) FREE p's
-					 * swap block? */
 				} else {
 					/* pageout was a success... */
 					pmap_clear_reference(p);