Coalesce pipe allocations and frees. Previously, the pipe code

would allocate two 'struct pipe's from the pipe zone, and malloc a
mutex.

- Create a new "struct pipepair" object holding the two 'struct
  pipe' instances, struct mutex, and struct label reference.  Pipe
  structures now have a back-pointer to the pipe pair, and a
  'pipe_present' flag to indicate whether the half has been
  closed.

- Perform mutex init/destroy in zone init/destroy, avoiding
  reallocating the mutex for each pipe.  Perform most pipe structure
  setup in zone constructor.

- VM memory mappings for pageable buffers are still done outside of
  the UMA zone.

- Change MAC API to speak 'struct pipepair' instead of 'struct pipe',
  update many policies.  MAC labels are also handled outside of the
  UMA zone for now.  Label-only policy modules don't have to be
  recompiled, but if a module is recompiled, its pipe entry points
  will need to be updated.  If a module actually reached into the
  pipe structures (unlikely), that would also need to be modified.

These changes substantially simplify failure handling in the pipe
code as there are many fewer possible failure modes.

On half-close, pipes no longer free the 'struct pipe' for the closed
half until a full-close takes place.  However, VM mapped buffers
are still released on half-close.

Some code refactoring is now possible to clean up some of the back
references, etc; this patch attempts not to change the structure
of most of the pipe implementation, only allocation/free code
paths, so as to avoid introducing bugs (hopefully).

This cuts about 8%-9% off the cost of sequential pipe allocation
and free in system call tests on UP and SMP in my micro-benchmarks.
May or may not make a difference in macro-benchmarks, but doing
less work is good.

Reviewed by:	juli, tjr
Testing help:	dwhite, fenestro, scottl, et al

1 files changed, 150 insertions, 91 deletions

diff --git a/sys/kern/sys_pipe.c b/sys/kern/sys_pipe.c
index 0f025d3..7045164 100644
--- a/sys/kern/sys_pipe.c
+++ b/sys/kern/sys_pipe.c
@@ -179,7 +179,7 @@ SYSCTL_INT(_kern_ipc, OID_AUTO, pipekvawired, CTLFLAG_RD,
 static void pipeinit(void *dummy __unused);
 static void pipeclose(struct pipe *cpipe);
 static void pipe_free_kmem(struct pipe *cpipe);
-static int pipe_create(struct pipe **cpipep);
+static int pipe_create(struct pipe *pipe);
 static __inline int pipelock(struct pipe *cpipe, int catch);
 static __inline void pipeunlock(struct pipe *cpipe);
 static __inline void pipeselwakeup(struct pipe *cpipe);
@@ -191,6 +191,11 @@ static void pipe_clone_write_buffer(struct pipe *wpipe);
 #endif
 static int pipespace(struct pipe *cpipe, int size);
 
+static void	pipe_zone_ctor(void *mem, int size, void *arg);
+static void	pipe_zone_dtor(void *mem, int size, void *arg);
+static void	pipe_zone_init(void *mem, int size);
+static void	pipe_zone_fini(void *mem, int size);
+
 static uma_zone_t pipe_zone;
 
 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_ANY, pipeinit, NULL);
@@ -199,13 +204,96 @@ static void
 pipeinit(void *dummy __unused)
 {
 
-	pipe_zone = uma_zcreate("PIPE", sizeof(struct pipe), NULL,
-	    NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
+	pipe_zone = uma_zcreate("PIPE", sizeof(struct pipepair),
+	    pipe_zone_ctor, pipe_zone_dtor, pipe_zone_init, pipe_zone_fini,
+	    UMA_ALIGN_PTR, 0);
 	KASSERT(pipe_zone != NULL, ("pipe_zone not initialized"));
 }
 
+static void
+pipe_zone_ctor(void *mem, int size, void *arg)
+{
+	struct pipepair *pp;
+	struct pipe *rpipe, *wpipe;
+
+	KASSERT(size == sizeof(*pp), ("pipe_zone_ctor: wrong size"));
+
+	pp = (struct pipepair *)mem;
+
+	/*
+	 * We zero both pipe endpoints to make sure all the kmem pointers
+	 * are NULL, flag fields are zero'd, etc.  We timestamp both
+	 * endpoints with the same time.
+	 */
+	rpipe = &pp->pp_rpipe;
+	bzero(rpipe, sizeof(*rpipe));
+	vfs_timestamp(&rpipe->pipe_ctime);
+	rpipe->pipe_atime = rpipe->pipe_mtime = rpipe->pipe_ctime;
+
+	wpipe = &pp->pp_wpipe;
+	bzero(wpipe, sizeof(*wpipe));
+	wpipe->pipe_ctime = rpipe->pipe_ctime;
+	wpipe->pipe_atime = wpipe->pipe_mtime = rpipe->pipe_ctime;
+
+	rpipe->pipe_peer = wpipe;
+	rpipe->pipe_pair = pp;
+	wpipe->pipe_peer = rpipe;
+	wpipe->pipe_pair = pp;
+
+	/*
+	 * Mark both endpoints as present; they will later get free'd
+	 * one at a time.  When both are free'd, then the whole pair
+	 * is released.
+	 */
+	rpipe->pipe_present = 1;
+	wpipe->pipe_present = 1;
+
+	/*
+	 * Eventually, the MAC Framework may initialize the label
+	 * in ctor or init, but for now we do it elswhere to avoid
+	 * blocking in ctor or init.
+	 */
+	pp->pp_label = NULL;
+
+}
+
+static void
+pipe_zone_dtor(void *mem, int size, void *arg)
+{
+	struct pipepair *pp;
+
+	KASSERT(size == sizeof(*pp), ("pipe_zone_dtor: wrong size"));
+
+	pp = (struct pipepair *)mem;
+}
+
+static void
+pipe_zone_init(void *mem, int size)
+{
+	struct pipepair *pp;
+
+	KASSERT(size == sizeof(*pp), ("pipe_zone_init: wrong size"));
+
+	pp = (struct pipepair *)mem;
+
+	mtx_init(&pp->pp_mtx, "pipe mutex", NULL, MTX_DEF | MTX_RECURSE);
+}
+
+static void
+pipe_zone_fini(void *mem, int size)
+{
+	struct pipepair *pp;
+
+	KASSERT(size == sizeof(*pp), ("pipe_zone_fini: wrong size"));
+
+	pp = (struct pipepair *)mem;
+
+	mtx_destroy(&pp->pp_mtx);
+}
+
 /*
- * The pipe system call for the DTYPE_PIPE type of pipes
+ * The pipe system call for the DTYPE_PIPE type of pipes.  If we fail,
+ * let the zone pick up the pieces via pipeclose().
  */
 
 /* ARGSUSED */
@@ -218,12 +306,25 @@ pipe(td, uap)
 {
 	struct filedesc *fdp = td->td_proc->p_fd;
 	struct file *rf, *wf;
+	struct pipepair *pp;
 	struct pipe *rpipe, *wpipe;
-	struct mtx *pmtx;
 	int fd, error;
 
-	rpipe = wpipe = NULL;
-	if (pipe_create(&rpipe) || pipe_create(&wpipe)) {
+	pp = uma_zalloc(pipe_zone, M_WAITOK);
+#ifdef MAC
+	/*
+	 * struct pipe represents a pipe endpoint.  The MAC label is shared
+	 * between the connected endpoints.  As a result mac_init_pipe() and
+	 * mac_create_pipe() should only be called on one of the endpoints
+	 * after they have been connected.
+	 */
+	mac_init_pipe(pp);
+	mac_create_pipe(td->td_ucred, pp);
+#endif
+	rpipe = &pp->pp_rpipe;
+	wpipe = &pp->pp_wpipe;
+
+	if (pipe_create(rpipe) || pipe_create(wpipe)) {
 		pipeclose(rpipe);
 		pipeclose(wpipe);
 		return (ENFILE);
@@ -278,21 +379,6 @@ pipe(td, uap)
 	FILE_UNLOCK(wf);
 	fdrop(wf, td);
 	td->td_retval[1] = fd;
-	rpipe->pipe_peer = wpipe;
-	wpipe->pipe_peer = rpipe;
-#ifdef MAC
-	/*
-	 * struct pipe represents a pipe endpoint.  The MAC label is shared
-	 * between the connected endpoints.  As a result mac_init_pipe() and
-	 * mac_create_pipe() should only be called on one of the endpoints
-	 * after they have been connected.
-	 */
-	mac_init_pipe(rpipe);
-	mac_create_pipe(td->td_ucred, rpipe);
-#endif
-	pmtx = malloc(sizeof(*pmtx), M_TEMP, M_WAITOK | M_ZERO);
-	mtx_init(pmtx, "pipe mutex", NULL, MTX_DEF | MTX_RECURSE);
-	rpipe->pipe_mtxp = wpipe->pipe_mtxp = pmtx;
 	fdrop(rf, td);
 
 	return (0);
@@ -314,8 +400,7 @@ pipespace(cpipe, size)
 	static int curfail = 0;
 	static struct timeval lastfail;
 
-	KASSERT(cpipe->pipe_mtxp == NULL || !mtx_owned(PIPE_MTX(cpipe)),
-	       ("pipespace: pipe mutex locked"));
+	KASSERT(!mtx_owned(PIPE_MTX(cpipe)), ("pipespace: pipe mutex locked"));
 
 	size = round_page(size);
 	/*
@@ -349,60 +434,28 @@ pipespace(cpipe, size)
 }
 
 /*
- * initialize and allocate VM and memory for pipe
+ * Initialize and allocate VM and memory for pipe.  The structure
+ * will start out zero'd from the ctor, so we just manage the kmem.
  */
 static int
-pipe_create(cpipep)
-	struct pipe **cpipep;
+pipe_create(pipe)
+	struct pipe *pipe;
 {
-	struct pipe *cpipe;
 	int error;
 
-	*cpipep = uma_zalloc(pipe_zone, M_WAITOK);
-	if (*cpipep == NULL)
-		return (ENOMEM);
-
-	cpipe = *cpipep;
-
-	/*
-	 * protect so pipeclose() doesn't follow a junk pointer
-	 * if pipespace() fails.
-	 */
-	bzero(&cpipe->pipe_sel, sizeof(cpipe->pipe_sel));
-	cpipe->pipe_state = 0;
-	cpipe->pipe_peer = NULL;
-	cpipe->pipe_busy = 0;
-
-#ifndef PIPE_NODIRECT
-	/*
-	 * pipe data structure initializations to support direct pipe I/O
-	 */
-	cpipe->pipe_map.cnt = 0;
-	cpipe->pipe_map.kva = 0;
-	cpipe->pipe_map.pos = 0;
-	cpipe->pipe_map.npages = 0;
-	/* cpipe->pipe_map.ms[] = invalid */
-#endif
-
-	cpipe->pipe_mtxp = NULL;	/* avoid pipespace assertion */
 	/*
 	 * Reduce to 1/4th pipe size if we're over our global max.
 	 */
 	if (amountpipekva > maxpipekva / 2)
-		error = pipespace(cpipe, SMALL_PIPE_SIZE);
+		error = pipespace(pipe, SMALL_PIPE_SIZE);
 	else
-		error = pipespace(cpipe, PIPE_SIZE);
+		error = pipespace(pipe, PIPE_SIZE);
 	if (error)
 		return (error);
 
-	vfs_timestamp(&cpipe->pipe_ctime);
-	cpipe->pipe_atime = cpipe->pipe_ctime;
-	cpipe->pipe_mtime = cpipe->pipe_ctime;
-
 	return (0);
 }
 
-
 /*
  * lock a pipe for I/O, blocking other access
  */
@@ -477,7 +530,7 @@ pipe_read(fp, uio, active_cred, flags, td)
 		goto unlocked_error;
 
 #ifdef MAC
-	error = mac_check_pipe_read(active_cred, rpipe);
+	error = mac_check_pipe_read(active_cred, rpipe->pipe_pair);
 	if (error)
 		goto locked_error;
 #endif
@@ -890,7 +943,7 @@ pipe_write(fp, uio, active_cred, flags, td)
 		return (EPIPE);
 	}
 #ifdef MAC
-	error = mac_check_pipe_write(active_cred, wpipe);
+	error = mac_check_pipe_write(active_cred, wpipe->pipe_pair);
 	if (error) {
 		PIPE_UNLOCK(rpipe);
 		return (error);
@@ -1180,7 +1233,7 @@ pipe_ioctl(fp, cmd, data, active_cred, td)
 	PIPE_LOCK(mpipe);
 
 #ifdef MAC
-	error = mac_check_pipe_ioctl(active_cred, mpipe, cmd, data);
+	error = mac_check_pipe_ioctl(active_cred, mpipe->pipe_pair, cmd, data);
 	if (error) {
 		PIPE_UNLOCK(mpipe);
 		return (error);
@@ -1252,7 +1305,7 @@ pipe_poll(fp, events, active_cred, td)
 	wpipe = rpipe->pipe_peer;
 	PIPE_LOCK(rpipe);
 #ifdef MAC
-	error = mac_check_pipe_poll(active_cred, rpipe);
+	error = mac_check_pipe_poll(active_cred, rpipe->pipe_pair);
 	if (error)
 		goto locked_error;
 #endif
@@ -1308,7 +1361,7 @@ pipe_stat(fp, ub, active_cred, td)
 	int error;
 
 	PIPE_LOCK(pipe);
-	error = mac_check_pipe_stat(active_cred, pipe);
+	error = mac_check_pipe_stat(active_cred, pipe->pipe_pair);
 	PIPE_UNLOCK(pipe);
 	if (error)
 		return (error);
@@ -1350,8 +1403,8 @@ pipe_free_kmem(cpipe)
 	struct pipe *cpipe;
 {
 
-	KASSERT(cpipe->pipe_mtxp == NULL || !mtx_owned(PIPE_MTX(cpipe)),
-	       ("pipe_free_kmem: pipe mutex locked"));
+	KASSERT(!mtx_owned(PIPE_MTX(cpipe)),
+	    ("pipe_free_kmem: pipe mutex locked"));
 
 	if (cpipe->pipe_buffer.buffer != NULL) {
 		if (cpipe->pipe_buffer.size > PIPE_SIZE)
@@ -1385,17 +1438,15 @@ static void
 pipeclose(cpipe)
 	struct pipe *cpipe;
 {
+	struct pipepair *pp;
 	struct pipe *ppipe;
 	int hadpeer;
 
-	if (cpipe == NULL)
-		return;
+	KASSERT(cpipe != NULL, ("pipeclose: cpipe == NULL"));
 
 	hadpeer = 0;
-
-	/* partially created pipes won't have a valid mutex. */
-	if (PIPE_MTX(cpipe) != NULL)
-		PIPE_LOCK(cpipe);
+	PIPE_LOCK(cpipe);
+	pp = cpipe->pipe_pair;
 
 	pipeselwakeup(cpipe);
 
@@ -1409,35 +1460,43 @@ pipeclose(cpipe)
 		msleep(cpipe, PIPE_MTX(cpipe), PRIBIO, "pipecl", 0);
 	}
 
-#ifdef MAC
-	if (cpipe->pipe_label != NULL && cpipe->pipe_peer == NULL)
-		mac_destroy_pipe(cpipe);
-#endif
 
 	/*
-	 * Disconnect from peer
+	 * Disconnect from peer, if any.
 	 */
-	if ((ppipe = cpipe->pipe_peer) != NULL) {
+	ppipe = cpipe->pipe_peer;
+	if (ppipe->pipe_present != 0) {
 		hadpeer++;
 		pipeselwakeup(ppipe);
 
 		ppipe->pipe_state |= PIPE_EOF;
 		wakeup(ppipe);
 		KNOTE(&ppipe->pipe_sel.si_note, 0);
-		ppipe->pipe_peer = NULL;
 	}
+
 	/*
-	 * free resources
+	 * Mark this endpoint as free.  Release kmem resources.  We
+	 * don't mark this endpoint as unused until we've finished
+	 * doing that, or the pipe might disappear out from under
+	 * us.
 	 */
-	if (PIPE_MTX(cpipe) != NULL) {
-		PIPE_UNLOCK(cpipe);
-		if (!hadpeer) {
-			mtx_destroy(PIPE_MTX(cpipe));
-			free(PIPE_MTX(cpipe), M_TEMP);
-		}
-	}
+	PIPE_UNLOCK(cpipe);
 	pipe_free_kmem(cpipe);
-	uma_zfree(pipe_zone, cpipe);
+	PIPE_LOCK(cpipe);
+	cpipe->pipe_present = 0;
+
+	/*
+	 * If both endpoints are now closed, release the memory for the
+	 * pipe pair.  If not, unlock.
+	 */
+	if (ppipe->pipe_present == 0) {
+		PIPE_UNLOCK(cpipe);
+#ifdef MAC
+		mac_destroy_pipe(pp);
+#endif
+		uma_zfree(pipe_zone, cpipe->pipe_pair);
+	} else
+		PIPE_UNLOCK(cpipe);
 }
 
 /*ARGSUSED*/