On Tue, 2 May 2017, Konstantin Belousov wrote:
On Wed, May 03, 2017 at 01:31:10AM +1000, Bruce Evans wrote:
On Tue, 2 May 2017, Konstantin Belousov wrote:
I also thought of changing the scale when the values get high. The values
would increase slower above about 2G instead of stabilizing at 4G-1.
This is basically floating point and too complicated since nothing would
understand it.
Which counters wrap faster than a reasonable refresh interval of 1-10
seconds (which should be shorter if wrapping is a problem)?
Things like various counters for pages freed due to a reason can. E.g.
freed due to the process exit is the counter which I saw changing fast.
4 billion page operations/second or 10 is impossible. It is difficult
to even increment a register to count events that fast.
Wire counts might fluctuate relatively quickly, but I think that wiring
is slower. Unwiring might be fast.
The need to zero pages before reuse limits the speed.
I just noticed that this sysctl is r/o (I thought I was preserving support
for resetting 64-bit counters using a 32-bit size in my fix in
sysctl_handle_counter_64(). That function has the dubious feature of not
checking the size, so it allows writes of any length (0 to SIZE_MAX,
possibly larger than the user data) to reset the counter to zero.)
The r/o misfeature goes back to at least FreeBSD-3. 64-bit counters need
resetting less than 32-bit ones, and it is more useful to ever reset them
since they can hold the full counts since boot time, but there is no reason
to limit resetting them now that the low-level code supports it. Is there
already a better atomic reset of all vm stats?
I do not see why vmstat counters ever need to be reset. I do not think
that truncating the value to present small values to 32bit readers is
a reasonable cause.
It would be mostly for presenting a consistent set of values.
diff --git a/sys/vm/vm_meter.c b/sys/vm/vm_meter.c
index 5f4cd46ab1e..b4666a400b2 100644
--- a/sys/vm/vm_meter.c
+++ b/sys/vm/vm_meter.c
@@ -266,8 +266,27 @@ static SYSCTL_NODE(_vm_stats, OID_AUTO, vm, CTLFLAG_RW, 0,
"VM meter vm stats");
SYSCTL_NODE(_vm_stats, OID_AUTO, misc, CTLFLAG_RW, 0, "VM meter misc stats");
+static int
+sysctl_handle_vmstat(SYSCTL_HANDLER_ARGS)
+{
+ uint64_t val;
+#ifdef COMPAT_FREEBSD11
+ uint32_t val32;
+#endif
+
+ val = counter_u64_fetch(*(counter_u64_t *)arg1);
+#ifdef COMPAT_FREEBSD11
+ if (req->oldlen == sizeof(val32)) {
+ val32 = val; /* truncate */
+ return (SYSCTL_OUT(req, &val32, sizeof(val32)));
+ }
+#endif
+ return (SYSCTL_OUT(req, &val, sizeof(val)));
+}
+
#define VM_STATS(parent, var, descr) \
- SYSCTL_COUNTER_U64(parent, OID_AUTO, var, CTLFLAG_RD, &vm_cnt.var, descr)
+ SYSCTL_OID(parent, OID_AUTO, var, CTLTYPE_U64 | CTLFLAG_MPSAFE | \
+ CTLFLAG_RD, &vm_cnt.var, 0, sysctl_handle_vmstat, "QU", descr);
#define VM_STATS_VM(var, descr) VM_STATS(_vm_stats_vm, var, descr)
#define VM_STATS_SYS(var, descr) VM_STATS(_vm_stats_sys, var, descr)
OK.
Bruce
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