svn commit: r192125 - head/sys/kern

[John Baldwin]

Author: jhb
Date: Thu May 14 22:01:32 2009
New Revision: 192125
URL: http://svn.freebsd.org/changeset/base/192125

Log:
  - Use a separate sx lock to try to limit the number of concurrent userland
    sysctl requests to avoid wiring too much user memory.  Only grab this
    lock if the user's old buffer is larger than a page as a tradeoff to
    allow more concurrency for common small requests.
  - Just use a shared lock on the sysctl tree for user sysctl requests now.
  
  MFC after:	1 week

Modified:
  head/sys/kern/kern_sysctl.c

Modified: head/sys/kern/kern_sysctl.c
==============================================================================
--- head/sys/kern/kern_sysctl.c	Thu May 14 22:01:14 2009	(r192124)
+++ head/sys/kern/kern_sysctl.c	Thu May 14 22:01:32 2009	(r192125)
@@ -77,11 +77,12 @@ static MALLOC_DEFINE(M_SYSCTLTMP, "sysct
  * API rather than using the dynamic API.  Use of the dynamic API is
  * strongly encouraged for most code.
  *
- * This lock is also used to serialize userland sysctl requests.  Some
- * sysctls wire user memory, and serializing the requests limits the
- * amount of wired user memory in use.
+ * The sysctlmemlock is used to limit the amount of user memory wired for
+ * sysctl requests.  This is implemented by serializing any userland
+ * sysctl requests larger than a single page via an exclusive lock.
  */
 static struct sx sysctllock;
+static struct sx sysctlmemlock;
 
 #define	SYSCTL_SLOCK()		sx_slock(&sysctllock)
 #define	SYSCTL_SUNLOCK()	sx_sunlock(&sysctllock)
@@ -543,6 +544,7 @@ sysctl_register_all(void *arg)
 {
 	struct sysctl_oid **oidp;
 
+	sx_init(&sysctlmemlock, "sysctl mem");
 	SYSCTL_INIT();
 	SYSCTL_XLOCK();
 	SET_FOREACH(oidp, sysctl_set)
@@ -1565,7 +1567,7 @@ userland_sysctl(struct thread *td, int *
     size_t *oldlenp, int inkernel, void *new, size_t newlen, size_t *retval,
     int flags)
 {
-	int error = 0;
+	int error = 0, memlocked;
 	struct sysctl_req req;
 
 	bzero(&req, sizeof req);
@@ -1605,14 +1607,20 @@ userland_sysctl(struct thread *td, int *
 	if (KTRPOINT(curthread, KTR_SYSCTL))
 		ktrsysctl(name, namelen);
 #endif
-	
-	SYSCTL_XLOCK();
+
+	if (req.oldlen > PAGE_SIZE) {
+		memlocked = 1;
+		sx_xlock(&sysctlmemlock);
+	} else
+		memlocked = 0;
 	CURVNET_SET(TD_TO_VNET(curthread));
 
 	for (;;) {
 		req.oldidx = 0;
 		req.newidx = 0;
+		SYSCTL_SLOCK();
 		error = sysctl_root(0, name, namelen, &req);
+		SYSCTL_SUNLOCK();
 		if (error != EAGAIN)
 			break;
 		uio_yield();
@@ -1622,7 +1630,8 @@ userland_sysctl(struct thread *td, int *
 
 	if (req.lock == REQ_WIRED && req.validlen > 0)
 		vsunlock(req.oldptr, req.validlen);
-	SYSCTL_XUNLOCK();
+	if (memlocked)
+		sx_xunlock(&sysctlmemlock);
 
 	if (error && error != ENOMEM)
 		return (error);