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kernel: make mntcache effective, be carefull

--- a/sys/src/9/port/cache.c

+++ b/sys/src/9/port/cache.c

@@ -113,10 +113,8 @@

 		panic("cinit: no memory");

 	/* a better algorithm would be nice */

-//	if(conf.npage*BY2PG > 200*MB)

-//		maxcache = 10*MAXCACHE;

-//	if(conf.npage*BY2PG > 400*MB)

-//		maxcache = 50*MAXCACHE;

+	if(conf.npage*BY2PG > 200*MB)

+		maxcache = 10*MAXCACHE;

 	for(i = 0; i < NFILE-1; i++) {

 		m->next = m+1;

@@ -171,17 +169,16 @@

 void

 cnodata(Mntcache *m)

 {

-	Extent *e, *n;

+	Extent *e;

 	/*

 	 * Invalidate all extent data

 	 * Image lru will waste the pages

 	 */

-	for(e = m->list; e; e = n) {

-		n = e->next;

+	while(e = m->list){

+		m->list = e->next;

 		extentfree(e);

 	}

-	m->list = 0;

 }

 void

@@ -215,13 +212,11 @@

 copen(Chan *c)

 {

 	int h;

-	Extent *e, *next;

 	Mntcache *m, *f, **l;

 	/* directories aren't cacheable and append-only files confuse us */

 	if(c->qid.type&(QTDIR|QTAPPEND))

 		return;

-

 	h = c->qid.path%NHASH;

 	lock(&cache);

 	for(m = cache.hash[h]; m; m = m->hash) {

@@ -228,17 +223,16 @@

 		if(m->qid.path == c->qid.path)

 		if(m->qid.type == c->qid.type)

 		if(m->dev == c->dev && m->type == c->type) {

-			c->mcp = m;

-			ctail(m);

-			unlock(&cache);

-

 			/* File was updated, invalidate cache */

-			if(m->qid.vers != c->qid.vers) {

+			if(m->qid.vers != c->qid.vers){

+				if(!canqlock(m))

+					goto Busy;

 				m->qid.vers = c->qid.vers;

-				qlock(m);

-				cnodata(m);

-				qunlock(m);

+				goto Update;

 			}

+			ctail(m);

+			c->mcp = m;

+			unlock(&cache);

 			return;

 		}

 	}

@@ -245,6 +239,8 @@

 	/* LRU the cache headers */

 	m = cache.head;

+	if(!canqlock(m))

+		goto Busy;

 	l = &cache.hash[m->qid.path%NHASH];

 	for(f = *l; f; f = f->hash) {

 		if(f == m) {

@@ -261,20 +257,16 @@

 	l = &cache.hash[h];

 	m->hash = *l;

 	*l = m;

+Update:

 	ctail(m);

-

-	qlock(m);

 	c->mcp = m;

-	e = m->list;

-	m->list = 0;

 	unlock(&cache);

-

-	while(e) {

-		next = e->next;

-		extentfree(e);

-		e = next;

-	}

+	cnodata(m);

 	qunlock(m);

+	return;

+Busy:

+	unlock(&cache);

+	c->mcp = 0;

 }

 static int

@@ -313,6 +305,7 @@

 	qlock(m);

 	if(cdev(m, c) == 0) {

 		qunlock(m);

+		c->mcp = 0;

 		return 0;

 	}

@@ -483,6 +476,7 @@

 	qlock(m);

 	if(cdev(m, c) == 0) {

 		qunlock(m);

+		c->mcp = 0;

 		return;

 	}

@@ -541,7 +535,9 @@

 			len -= o;

 			offset += o;

 			if(len <= 0) {

-if(f && p->start + p->len > f->start) print("CACHE: p->start=%uld p->len=%d f->start=%uld\n", p->start, p->len, f->start);

+				if(f && p->start + p->len > f->start)

+					print("CACHE: p->start=%uld p->len=%d f->start=%uld\n",

+						p->start, p->len, f->start);

 				qunlock(m);

 				return;

 			}

@@ -575,6 +571,7 @@

 	qlock(m);

 	if(cdev(m, c) == 0) {

 		qunlock(m);

+		c->mcp = 0;

 		return;

 	}

--- a/sys/src/9/port/chan.c

+++ b/sys/src/9/port/chan.c

@@ -1488,9 +1488,6 @@

 			/* save registers else error() in open has wrong value of c saved */

 			saveregisters();

-			if(omode == OEXEC)

-				c->flag &= ~CCACHE;

-

 			c = devtab[c->type]->open(c, omode&~OCEXEC);

 			if(omode & OCEXEC)

--- a/sys/src/9/port/devmnt.c

+++ b/sys/src/9/port/devmnt.c

@@ -409,6 +409,7 @@

 		 * Therefore set type to 0 for now; rootclose is known to be safe.

 		 */

 		nc->type = 0;

+		nc->flag |= (c->flag & CCACHE);

 		alloc = 1;

 	}

 	wq->clone = nc;

--- a/sys/src/9/port/fault.c

+++ b/sys/src/9/port/fault.c

@@ -200,7 +200,7 @@

 	Page *new;

 	KMap *k;

 	Chan *c;

-	int n, ask;

+	int n, ask, cache;

 	char *kaddr;

 	ulong daddr;

 	Page *loadrec;

@@ -238,7 +238,9 @@

 	k = kmap(new);

 	kaddr = (char*)VA(k);

+	cache = c->flag & CCACHE;

 	while(waserror()) {

+		c->flag |= cache;

 		if(strcmp(up->errstr, Eintr) == 0)

 			continue;

 		kunmap(k);

@@ -245,8 +247,9 @@

 		putpage(new);

 		faulterror(Eioload, c, 0);

 	}

-

+	c->flag &= ~CCACHE;

 	n = devtab[c->type]->read(c, kaddr, ask, daddr);

+	c->flag |= cache;

 	if(n != ask)

 		faulterror(Eioload, c, 0);

 	if(ask < BY2PG)