svn commit: r317061 - in head: libexec/rpc.rstatd sys/amd64/amd64 sys/amd64/include sys/arm/arm sys/arm/include sys/arm64/include sys/cddl/contrib/opensolaris/uts/common/fs/zfs sys/compat/linprocfs...

[Konstantin Belousov]

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.

Wire counts might fluctuate relatively quickly, but I think that wiring
is slower.  Unwiring might be fast.

> Style:
> - redundant cast.  Especially not needed with the commit.  Compilers might
>    warn about this since they don't trust programmers, but don't because
>    implicit downwards conversions are used often.
> - comment not indented
> 
> I would also omit the ifdefs, and rename 'out' to out64, and may rename
> 'out*' to val*.
Ok.

> 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.

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)