type of vm.stats.vm.v_vnodepgsin vm.stats.vm.v_swappgsin, vm.stats.vm.v_vnodepgsout vm.stats.vm.v_swappgsout on AMD64 r320730

[Konstantin Belousov]

On Mon, Jul 10, 2017 at 03:40:46PM +0900, Tomoaki AOKI wrote:
> Hi.
> 
> Members v_swappgsin and v_vnodepgsin are declared on sys/sys/vmmeter.h
> as
> 
>   u_int         on stable/11 at r320798 [1]
>   counter_u64_t on head at r320861      [2]
> 
> respectively.
> 
> Diggin in further, on head at r320861, counter_u64_t is typedef'ed as
> uint64_t * at line 32 of sys/sys/counter.h [3] like below.
> 
>   typedef uint64_t *counter_u64_t;
> 
> So they're "pointers" on head, while "values" on stable/11.
> 
> So, as you're on head, it seems you're casting "pointers (addresses)" to
> uint64_t "value". It could be huge and non-expected values.
> Your code would work as expected on stable/11. 

What ?  counter_u64_t in userspace in nonsense.

Whole struct vmmeter is useless in userspace, it is not exported by the
sysctls and is only used in kernel.  Sysctl MIBs export individual
counters which should be used with appropriate type, but besides native
uint64_t, 32bit requests are also supported.

This is why I asked about the type of the vm.v_something and asked for
the explicit fragment of the code which reads the MIBs.

> 
> [1]
> https://svnweb.freebsd.org/base/stable/11/sys/sys/vmmeter.h?annotate=320610
> 
> [2]
> https://svnweb.freebsd.org/base/head/sys/sys/vmmeter.h?annotate=317061
> 
> [3]
> https://svnweb.freebsd.org/base/head/sys/sys/counter.h?annotate=309745
> 
> 
> On Sun, 9 Jul 2017 23:15:18 -0300
> Otac?$B".lio <otacilio.neto at bsd.com.br> wrote:
> 
> > Dears
> > 
> > I'm the maintainer of xosview and I'm debugging rather weird behavior 
> > from it in the latest FreeBSD 12 revisions (12.0-CURRENT #0 r320730 
> > AMD64) . The problem is occurring on the lines responsible for 
> > collecting statistics about paging. These lines follow:
> > 
> > If (pageinfo) {
> > Pageinfo [0] = (uint64_t) vm.v_vnodepgsin + (uint64_t) vm.v_swappgsin;
> > Pageinfo [1] = (uint64_t) vm.v_vnodepgsout + (uint64_t) vm.v_swappgsout;
> > }
> > 
> > This code works on FreeBSD 11 and until a short time ago it works at 12. 
> > But now it returns extremely large values ?$B".".when interpreted as 64-bit 
> > values. A debugging has shown that for this sysctl call the following 
> > values ?$B".".are returned in the terminal:
> > sysctl vm.stats.vm.v_vnodepgsin vm.stats.vm.v_swappgsin 
> > vm.stats.vm.v_vnodepgsout vm.stats.vm.v_swappgsout
> > Vm.stats.vm.v_vnodepgsin: 47432
> > Vm.stats.vm.v_swappgsin: 0
> > Vm.stats.vm.v_vnodepgsout: 19
> > Vm.stats.vm.v_swappgsout: 0
> > 
> > While the code returns things like:
> > 
> > Pageinf [0] = 34359785800; Pageinfo [1] = 140733193388051
> > Pageinf [0] = 34359785800; Pageinfo [1] = 2678138638516092947
> > 
> > After some tests I found that if I change the code to use a typecast to 
> > (uint32_t) then Xosview works correctly.:
> > If (pageinfo) {
> > Pageinfo [0] = (uint32_t) ((uint64_t) vm.v_vnodepgsin + (uint64_t) 
> > vm.v_swappgsin);
> > Pageinfo [1] = (uint32_t) ((uint64_t) vm.v_vnodepgsout + (uint64_t) 
> > vm.v_swappgsout);
> > }
> > 
> > For me, it seems that some code in the kernel is storing values ?$B".".as 32 
> > bits where it should be 64 bits. Is this behavior correct?
> > 
> > []'s
> > 
> > -Otac?$B".lio
> > _______________________________________________
> > freebsd-current at freebsd.org mailing list
> > https://lists.freebsd.org/mailman/listinfo/freebsd-current
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> > 
> > 
> 
> 
> -- 
> Tomoaki AOKI    <junchoon at dec.sakura.ne.jp>
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