devswap: simplify, don't panic when writing swapfile fails

always start the pager kproc in swapinit(), simplifying kickpager().

allow zero conf.nswap and conf.nswppo. avoid allocating the reference
map and iolist arrays in that case.

use ulong for ioptr and iolist indices.

don't panic when writing pages out to the swapfile fails. just
requeue the page in the io transaction list so we will try
again next time executeio() is run or just free the page when
the swap reference was dropped.

remove unused pagersummary() function.

1 files changed, 35 insertions, 43 deletions

diff --git a/sys/src/9/port/devswap.c b/sys/src/9/port/devswap.c
index 7cd4446c1..745303d74 100644
--- a/sys/src/9/port/devswap.c
+++ b/sys/src/9/port/devswap.c
@@ -23,23 +23,35 @@ static uchar	*swapbuf;
 static AESstate *swapkey;
 
 static Page	**iolist;
-static int	ioptr;
+static ulong	ioptr;
 
 static ushort	ageclock;
 
 static void
 swapinit(void)
 {
-	swapalloc.swmap = xalloc(conf.nswap);
+	while(conf.nswap && conf.nswppo){
+		swapalloc.swmap = xalloc(conf.nswap);
+		if(swapalloc.swmap == nil)
+			break;
+		iolist = xalloc(conf.nswppo*sizeof(Page*));
+		if(iolist == nil){
+			xfree(swapalloc.swmap);
+			swapalloc.swmap = nil;
+		}
+		break;
+	}
+
+	if(swapalloc.swmap == nil || iolist == nil)
+		conf.nswap = conf.nswppo = 0;
+
 	swapalloc.top = &swapalloc.swmap[conf.nswap];
 	swapalloc.alloc = swapalloc.swmap;
 	swapalloc.last = swapalloc.swmap;
 	swapalloc.free = conf.nswap;
 	swapalloc.xref = 0;
 
-	iolist = xalloc(conf.nswppo*sizeof(Page*));
-	if(swapalloc.swmap == nil || iolist == nil)
-		panic("swapinit: not enough memory");
+	kproc("pager", pager, 0);
 }
 
 static uintptr
@@ -116,12 +128,7 @@ swapcount(uintptr daddr)
 void
 kickpager(void)
 {
-	static Ref started;
-
-	if(started.ref || incref(&started) != 1)
-		wakeup(&swapalloc.r);
-	else
-		kproc("pager", pager, 0);
+	wakeup(&swapalloc.r);
 }
 
 static int
@@ -204,7 +211,7 @@ pager(void*)
 		}
 		qunlock(&p->seglock);
 
-		if(ioptr > 0) {
+		if(ioptr) {
 			up->psstate = "I/O";
 			executeio();
 		}
@@ -331,28 +338,13 @@ pagepte(int type, Page **pg)
 	}
 }
 
-void
-pagersummary(void)
-{
-	print("%lud/%lud memory %lud/%lud swap %d iolist\n",
-		palloc.user-palloc.freecount,
-		palloc.user, conf.nswap-swapalloc.free, conf.nswap,
-		ioptr);
-}
-
 static void
 executeio(void)
 {
 	Page *outp;
-	int i, n;
-	Chan *c;
-	char *kaddr;
-	KMap *k;
-
-	c = swapimage.c;
-	for(i = 0; i < ioptr; i++) {
-		if(ioptr > conf.nswppo)
-			panic("executeio: ioptr %d > %d", ioptr, conf.nswppo);
+	ulong i, j;
+
+	for(i = j = 0; i < ioptr; i++) {
 		outp = iolist[i];
 
 		assert(outp->ref > 0);
@@ -361,16 +353,15 @@ executeio(void)
 
 		/* only write when swap address still in use */
 		if(swapcount(outp->daddr) > 1){
-			k = kmap(outp);
-			kaddr = (char*)VA(k);
-
-			if(waserror())
-				panic("executeio: page outp I/O error");
-
-			n = devtab[c->type]->write(c, kaddr, BY2PG, outp->daddr);
-			if(n != BY2PG)
-				nexterror();
-
+			Chan *c = swapimage.c;
+			KMap *k = kmap(outp);
+			if(waserror()){
+				kunmap(k);
+				iolist[j++] = outp;
+				continue;
+			}
+			if(devtab[c->type]->write(c, (char*)VA(k), BY2PG, outp->daddr) != BY2PG)
+				error(Eshort);
 			kunmap(k);
 			poperror();
 		}
@@ -381,7 +372,8 @@ executeio(void)
 		/* Free up the page after I/O */
 		putpage(outp);
 	}
-	ioptr = 0;
+	ioptr = j;
+	if(j) print("executeio (%lud/%lud): %s\n", j, i, up->errstr);
 }
 
 int
@@ -416,9 +408,9 @@ setswapchan(Chan *c)
 		n = devtab[c->type]->stat(c, buf, sizeof buf);
 		if(n <= 0 || convM2D(buf, n, &d, nil) == 0)
 			error("stat failed in setswapchan");
-		if(d.length < conf.nswppo*BY2PG)
+		if(d.length < (vlong)conf.nswppo*BY2PG)
 			error("swap device too small");
-		if(d.length < conf.nswap*BY2PG){
+		if(d.length < (vlong)conf.nswap*BY2PG){
 			conf.nswap = d.length/BY2PG;
 			swapalloc.top = &swapalloc.swmap[conf.nswap];
 			swapalloc.free = conf.nswap;