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- Use a separate sx lock to try to limit the number of concurrent userland

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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
This commit is contained in:
John Baldwin 2009-05-14 22:01:32 +00:00
parent 76dae09449
commit 3e829b18d6
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=192125
1 changed files with 16 additions and 7 deletions
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23
sys/kern/kern_sysctl.c
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@ -77,11 +77,12 @@ static MALLOC_DEFINE(M_SYSCTLTMP, "sysctltmp", "sysctl temp output buffer");
* 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 *name, u_int namelen, void *old,
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 *name, u_int namelen, void *old,
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 *name, u_int namelen, void *old,
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);