a better fix for the "uvm_km thread runs out of memory" problem.

add a new arg to the backend so it can tell pool to slow down.  when we get
this flag, yield *after* putting the page in the pool's free list.  whatever
we do, don't let the thread sleep.

this makes things better by still letting the thread run when a huge pf
request comes in, but without artificially increasing pressure on the backend
by eating pages without feeding them forward.

ok deraadt

1 files changed, 10 insertions, 8 deletions

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index 9356cb32039..41b8263819d 100644
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vfs_cache.c,v 1.27 2008/10/20 20:33:07 deraadt Exp $	*/
+/*	$OpenBSD: vfs_cache.c,v 1.28 2008/10/23 23:54:02 tedu Exp $	*/
 /*	$NetBSD: vfs_cache.c,v 1.13 1996/02/04 02:18:09 christos Exp $	*/
 
 /*
@@ -162,6 +162,9 @@ cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
 		goto remove;
 	}
 
+	/* remove from lru now to prevent races */
+	TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
+
 	vp = ncp->nc_vp;
 	vpid = vp->v_id;
 	if (vp == dvp) {	/* lookup on "." */
@@ -178,6 +181,8 @@ cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
 		if (!error && (~cnp->cn_flags & (LOCKPARENT|ISLASTCN)) == 0) {
 			if ((error = vn_lock(dvp, LK_EXCLUSIVE, p)) != 0) {
 				vput(vp);
+				/* parent has permanent issues; recycle */
+				TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru);
 				return (error);
 			}
 			cnp->cn_flags &= ~PDIRUNLOCK;
@@ -204,6 +209,8 @@ cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
 			nchstats.ncs_falsehits++;
 		} else
 			nchstats.ncs_badhits++;
+		/* cache entry is stale; recycle */
+		TAILQ_INSERT_HEAD(&nclruhead, ncp, nc_lru);
 		/*
 		 * The parent needs to be locked when we return to VOP_LOOKUP().
 		 * The `.' case here should be extremely rare (if it can happen
@@ -219,13 +226,8 @@ cache_lookup(struct vnode *dvp, struct vnode **vpp, struct componentname *cnp)
 	}
 
 	nchstats.ncs_goodhits++;
-	/*
-	 * Move this slot to end of LRU chain, if not already there.
-	 */
-	if (TAILQ_NEXT(ncp, nc_lru) != NULL) {
-		TAILQ_REMOVE(&nclruhead, ncp, nc_lru);
-		TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
-	}
+	/* cache entry is valid; keep it */
+	TAILQ_INSERT_TAIL(&nclruhead, ncp, nc_lru);
 	*vpp = vp;
 	return (0);