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Date:      Tue, 9 Apr 2013 15:35:27 +0000 (UTC)
From:      Steven Hartland <smh@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-8@freebsd.org
Subject:   svn commit: r249310 - in stable/8/sys: kern sys
Message-ID:  <201304091535.r39FZRgI049739@svn.freebsd.org>
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Author: smh
Date: Tue Apr  9 15:35:26 2013
New Revision: 249310
URL: http://svnweb.freebsd.org/changeset/base/249310

Log:
  MFC r241556:
  Add a KPI to allow to reserve some amount of space in the numvnodes
  counter, without actually allocating the vnodes.
  
  For KBI stability, the td_vp_reserv was moved to the end of struct thread.
  
  Reviewed by:	avg
  Approved by:	avg (co-mentor)

Modified:
  stable/8/sys/kern/kern_thread.c
  stable/8/sys/kern/subr_trap.c
  stable/8/sys/kern/vfs_subr.c
  stable/8/sys/sys/proc.h
  stable/8/sys/sys/vnode.h
Directory Properties:
  stable/8/sys/   (props changed)
  stable/8/sys/kern/   (props changed)
  stable/8/sys/sys/   (props changed)

Modified: stable/8/sys/kern/kern_thread.c
==============================================================================
--- stable/8/sys/kern/kern_thread.c	Tue Apr  9 15:15:52 2013	(r249309)
+++ stable/8/sys/kern/kern_thread.c	Tue Apr  9 15:35:26 2013	(r249310)
@@ -159,6 +159,7 @@ thread_init(void *mem, int size, int fla
 
 	td->td_sleepqueue = sleepq_alloc();
 	td->td_turnstile = turnstile_alloc();
+	td->td_vp_reserv = 0;
 	EVENTHANDLER_INVOKE(thread_init, td);
 	td->td_sched = (struct td_sched *)&td[1];
 	umtx_thread_init(td);

Modified: stable/8/sys/kern/subr_trap.c
==============================================================================
--- stable/8/sys/kern/subr_trap.c	Tue Apr  9 15:15:52 2013	(r249309)
+++ stable/8/sys/kern/subr_trap.c	Tue Apr  9 15:35:26 2013	(r249310)
@@ -132,6 +132,8 @@ userret(struct thread *td, struct trapfr
 	sched_userret(td);
 	KASSERT(td->td_locks == 0,
 	    ("userret: Returning with %d locks held.", td->td_locks));
+	KASSERT(td->td_vp_reserv == 0,
+	    ("userret: Returning while holding vnode reservation"));
 #ifdef VIMAGE
 	/* Unfortunately td_vnet_lpush needs VNET_DEBUG. */
 	VNET_ASSERT(curvnet == NULL,

Modified: stable/8/sys/kern/vfs_subr.c
==============================================================================
--- stable/8/sys/kern/vfs_subr.c	Tue Apr  9 15:15:52 2013	(r249309)
+++ stable/8/sys/kern/vfs_subr.c	Tue Apr  9 15:35:26 2013	(r249310)
@@ -977,34 +977,22 @@ vtryrecycle(struct vnode *vp)
 }
 
 /*
- * Return the next vnode from the free list.
+ * Wait for available vnodes.
  */
-int
-getnewvnode(const char *tag, struct mount *mp, struct vop_vector *vops,
-    struct vnode **vpp)
+static int
+getnewvnode_wait(int suspended)
 {
-	struct vnode *vp = NULL;
-	struct bufobj *bo;
 
-	CTR3(KTR_VFS, "%s: mp %p with tag %s", __func__, mp, tag);
-	mtx_lock(&vnode_free_list_mtx);
-	/*
-	 * Lend our context to reclaim vnodes if they've exceeded the max.
-	 */
-	if (freevnodes > wantfreevnodes)
-		vnlru_free(1);
-	/*
-	 * Wait for available vnodes.
-	 */
+	mtx_assert(&vnode_free_list_mtx, MA_OWNED);
 	if (numvnodes > desiredvnodes) {
-		if (mp != NULL && (mp->mnt_kern_flag & MNTK_SUSPEND)) {
+		if (suspended) {
 			/*
 			 * File system is beeing suspended, we cannot risk a
 			 * deadlock here, so allocate new vnode anyway.
 			 */
 			if (freevnodes > wantfreevnodes)
 				vnlru_free(freevnodes - wantfreevnodes);
-			goto alloc;
+			return (0);
 		}
 		if (vnlruproc_sig == 0) {
 			vnlruproc_sig = 1;	/* avoid unnecessary wakeups */
@@ -1012,16 +1000,76 @@ getnewvnode(const char *tag, struct moun
 		}
 		msleep(&vnlruproc_sig, &vnode_free_list_mtx, PVFS,
 		    "vlruwk", hz);
-#if 0	/* XXX Not all VFS_VGET/ffs_vget callers check returns. */
-		if (numvnodes > desiredvnodes) {
-			mtx_unlock(&vnode_free_list_mtx);
-			return (ENFILE);
+	}
+	return (numvnodes > desiredvnodes ? ENFILE : 0);
+}
+
+void
+getnewvnode_reserve(u_int count)
+{
+	struct thread *td;
+
+	td = curthread;
+	mtx_lock(&vnode_free_list_mtx);
+	while (count > 0) {
+		if (getnewvnode_wait(0) == 0) {
+			count--;
+			td->td_vp_reserv++;
+			numvnodes++;
 		}
-#endif
 	}
-alloc:
+	mtx_unlock(&vnode_free_list_mtx);
+}
+
+void
+getnewvnode_drop_reserve(void)
+{
+	struct thread *td;
+
+	td = curthread;
+	mtx_lock(&vnode_free_list_mtx);
+	KASSERT(numvnodes >= td->td_vp_reserv, ("reserve too large"));
+	numvnodes -= td->td_vp_reserv;
+	mtx_unlock(&vnode_free_list_mtx);
+	td->td_vp_reserv = 0;
+}
+
+/*
+ * Return the next vnode from the free list.
+ */
+int
+getnewvnode(const char *tag, struct mount *mp, struct vop_vector *vops,
+    struct vnode **vpp)
+{
+	struct vnode *vp;
+	struct bufobj *bo;
+	struct thread *td;
+	int error;
+
+	CTR3(KTR_VFS, "%s: mp %p with tag %s", __func__, mp, tag);
+	vp = NULL;
+	td = curthread;
+	if (td->td_vp_reserv > 0) {
+		td->td_vp_reserv -= 1;
+		goto alloc;
+	}
+	mtx_lock(&vnode_free_list_mtx);
+	/*
+	 * Lend our context to reclaim vnodes if they've exceeded the max.
+	 */
+	if (freevnodes > wantfreevnodes)
+		vnlru_free(1);
+	error = getnewvnode_wait(mp != NULL && (mp->mnt_kern_flag &
+	    MNTK_SUSPEND));
+#if 0	/* XXX Not all VFS_VGET/ffs_vget callers check returns. */
+	if (error != 0) {
+		mtx_unlock(&vnode_free_list_mtx);
+		return (error);
+	}
+#endif
 	numvnodes++;
 	mtx_unlock(&vnode_free_list_mtx);
+alloc:
 	vp = (struct vnode *) uma_zalloc(vnode_zone, M_WAITOK|M_ZERO);
 	/*
 	 * Setup locks.

Modified: stable/8/sys/sys/proc.h
==============================================================================
--- stable/8/sys/sys/proc.h	Tue Apr  9 15:15:52 2013	(r249309)
+++ stable/8/sys/sys/proc.h	Tue Apr  9 15:35:26 2013	(r249310)
@@ -308,6 +308,7 @@ struct thread {
 	struct rusage_ext td_rux;	/* (t) Internal rusage information. */
 	struct vm_map_entry *td_map_def_user; /* (k) Deferred entries. */
 	pid_t		td_dbg_forked;	/* (c) Child pid for debugger. */
+	u_int		td_vp_reserv;	/* (k) Count of reserved vnodes. */
 };
 
 struct mtx *thread_lock_block(struct thread *);

Modified: stable/8/sys/sys/vnode.h
==============================================================================
--- stable/8/sys/sys/vnode.h	Tue Apr  9 15:15:52 2013	(r249309)
+++ stable/8/sys/sys/vnode.h	Tue Apr  9 15:35:26 2013	(r249310)
@@ -604,6 +604,8 @@ void	cvtstat(struct stat *st, struct ost
 void	cvtnstat(struct stat *sb, struct nstat *nsb);
 int	getnewvnode(const char *tag, struct mount *mp, struct vop_vector *vops,
 	    struct vnode **vpp);
+void	getnewvnode_reserve(u_int count);
+void	getnewvnode_drop_reserve(void);
 int	insmntque1(struct vnode *vp, struct mount *mp,
 	    void (*dtr)(struct vnode *, void *), void *dtr_arg);
 int	insmntque(struct vnode *vp, struct mount *mp);

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