vminfo Provider

The vminfo provider makes available probes that correspond to the vm kernel statistics. Because these statistics provide the input for system monitoring utilities like vmstat(1M), the vminfo provider enables quick exploration of observed aberrant behavior.

24.1. Probes

The vminfo provider makes available probes that correspond to the fields in the vm named kernel statistic: a probe provided by vminfo fires immediately before the corresponding vm value is incremented. To display both the names and the current values of the vm named kernel statistic, use the kstat(1M) command, as shown in the following example:

$ kstat -n vm
module: cpu                             instance: 0
name:   vm                              class:    misc
        anonfree                        13
        anonpgin                        2620
        anonpgout                       13
        as_fault                        12528831
        cow_fault                       2278711
        crtime                          202.10625712
        dfree                           1328740
        execfree                        0
        execpgin                        5541
        ...

The vminfo probes are described in vminfo Probes.

vminfo Probes

anonfree

Probe that fires whenever an unmodified anonymous page is freed as part of paging activity. Anonymous pages are those that are not associated with a file. Memory containing such pages includes heap memory, stack memory, or memory obtained by explicitly mapping zero(7D).

anonpgin

Probe that fires whenever an anonymous page is paged in from a swap device.

anonpgout

Probe that fires whenever a modified anonymous page is paged out to a swap device.

as_fault

Probe that fires whenever a fault is taken on a page and the fault is neither a protection fault nor a copy-on-write fault.

cow_fault

Probe that fires whenever a copy-on-write fault is taken on a page. arg0 contains the number of pages that are created as a result of the copy-on-write.

dfree

Probe that fires whenever a page is freed as a result of paging activity. Whenever dfree fires, exactly one of anonfree, execfree or fsfree will also subsequently fire.

execfree

Probe that fires whenever an unmodified executable page is freed as a result of paging activity.

execpgin

Probe that fires whenever an executable page is paged in from the backing store.

execpgout

Probe that fires whenever a modified executable page is paged out to the backing store. Most paging of executable pages occurs in terms of execfree. execpgout can only fire if an executable page is modified in memory, an uncommon occurrence in most systems.

fsfree

Probe that fires whenever an unmodified file system data page is freed as part of paging activity.

fspgin

Probe that fires whenever a file system page is paged in from the backing store.

fspgout

Probe that fires whenever a modified file system page is paged out to the backing store.

kernel_asflt

Probe that fires whenever a page fault is taken by the kernel on a page in its own address space. Whenever kernel_asflt fires, it will be immediately preceded by a firing of the as_fault probe.

maj_fault

Probe that fires whenever a page fault is taken that results in I/O from a backing store or swap device. Whenever maj_fault fires, it will be immediately preceded by a firing of the pgin probe.

pgfrec

Probe that fires whenever a page is reclaimed off of the free page list.

pgin

Probe that fires whenever a page is paged in from the backing store or from a swap device. This probe differs from maj_fault in that maj_fault only fires when a page is paged in as a result of a page fault. pgin fires every time a page is paged in, regardless of the reason.

pgout

Probe that fires whenever a page is paged out to the backing store or to a swap device.

pgpgin

Probe that fires whenever a page is paged in from the backing store or from a swap device. The only difference between pgpgin and pgin is that pgpgin contains the number of pages paged in as arg0. (pgin always contains 1 in arg0.)

pgpgout

Probe that fires whenever a page is paged out to the backing store or to a swap device. The only difference between pgpgout and pgout is that pgpgout contains the number of pages paged out as arg0. (pgout always contains 1 in arg0.)

pgrec

Probe that fires whenever a page is reclaimed.

pgrrun

Probe that fires whenever the pager is scheduled.

pgswapin

Probe that fires whenever pages from a swapped-out process are swapped in. The number of pages swapped in is contained in arg0.

pgswapout

Probe that fires whenever pages are swapped out as part of swapping out a process. The number of pages swapped out is contained in arg0.

prot_fault

Probe that fires whenever a page fault is taken due to a protection violation.

rev

Probe that fires whenever the page daemon begins a new revolution through all pages.

scan

Probe that fires whenever the page daemon examines a page.

softlock

Probe that fires whenever a page is faulted as a part of placing a software lock on the page.

swapin

Probe that fires whenever a swapped-out process is swapped back in.

swapout

Probe that fires whenever a process is swapped out.

zfod

Probe that fires whenever a zero-filled page is created on demand.

24.2. Arguments

arg0

The value by which the statistic is to be incremented. For most probes, this argument is always 1, but for some it may take other values; these probes are noted in vminfo Probes.

arg1

A pointer to the current value of the statistic to be incremented. This value is a 64–bit quantity that will be incremented by the value in arg0. Dereferencing this pointer allows consumers to determine the current count of the statistic corresponding to the probe.

24.3. Example

Examine the following output from vmstat(1M):

kthr      memory            page            disk          faults      cpu
 r b w   swap  free  re  mf pi po fr de sr cd s0 — —   in   sy   cs us sy id
 0 1 0 1341844 836720 26 311 1644 0 0 0  0 216 0  0  0  797  817  697  9 10 81
 0 1 0 1341344 835300 238 934 1576 0 0 0 0 194 0  0  0  750 2795  791  7 14 79
 0 1 0 1340764 833668 24 165 1149 0 0 0  0 133 0  0  0  637  813  547  5  4 91
 0 1 0 1340420 833024 24 394 1002 0 0 0  0 130 0  0  0  621 2284  653 14  7 79
 0 1 0 1340068 831520 14 202 380 0 0  0  0 59  0  0  0  482 5688 1434 25  7 68

The pi column in the above output denotes the number of pages paged in. The vminfo provider enables you to learn more about the source of these page-ins, as shown in the following example:

dtrace -n pgin'{@[execname] = count()}'
dtrace: description 'pgin' matched 1 probe
^C
  xterm                                                             1
  ksh                                                               1
  ls                                                                2
  lpstat                                                            7
  sh                                                               17
  soffice                                                          39
  javaldx                                                         103
  soffice.bin                                                    3065

The output shows that a process associated with the StarOfficeTM software, soffice.bin, is responsible for most of the page-ins. To get a better picture of soffice.bin in terms of virtual memory behavior, you could enable all vminfo probes. The following example runs dtrace(1M) while launching the StarOffice software:

dtrace -P vminfo'/execname == "soffice.bin"/{@[probename] = count()}'
dtrace: description 'vminfo' matched 42 probes
^C

  kernel_asflt                                                      1
  fspgin                                                           10
  pgout                                                            16
  execfree                                                         16
  execpgout                                                        16
  fsfree                                                           16
  fspgout                                                          16
  anonfree                                                         16
  anonpgout                                                        16
  pgpgout                                                          16
  dfree                                                            16
  execpgin                                                         80
  prot_fault                                                       85
  maj_fault                                                        88
  pgin                                                             90
  pgpgin                                                           90
  cow_fault                                                       859
  zfod                                                           1619
  pgfrec                                                         8811
  pgrec                                                          8827
  as_fault                                                       9495

The following example script provides more information about the virtual memory behavior of the StarOffice software during its startup:

vminfo:::maj_fault,
vminfo:::zfod,
vminfo:::as_fault
/execname == "soffice.bin" && start == 0/
{
	/*
	 * This is the first time that a vminfo probe has been hit; record
	 * our initial timestamp.
	 */
	start = timestamp;
}

vminfo:::maj_fault,
vminfo:::zfod,
vminfo:::as_fault
/execname == "soffice.bin"/
{
	/*
	 * Aggregate on the probename, and lquantize() the number of seconds
	 * since our initial timestamp.  (There are 1,000,000,000 nanoseconds
	 * in a second.)  We assume that the script will be terminated before
	 * 60 seconds elapses.
	 */
	@[probename] =
	    lquantize((timestamp - start) / 1000000000, 0, 60);
}

Run the script while again starting the StarOffice software. Then, create a new drawing, create a new presentation, and then close all files and quit the application. Press Control-C in the shell running the D script. The results provide a view of some virtual memory behavior over time:

# dtrace -s ./soffice.d
dtrace: script './soffice.d' matched 10 probes
^C

 maj_fault
           value  ------------- Distribution ------------- count
               7 |                                         0
               8 |@@@@@@@@@                                88
               9 |@@@@@@@@@@@@@@@@@@@@                     194
              10 |@                                        18
              11 |                                         0
              12 |                                         0
              13 |                                         2
              14 |                                         0
              15 |                                         1
              16 |@@@@@@@@                                 82
              17 |                                         0
              18 |                                         0
              19 |                                         2
              20 |                                         0

  zfod
           value  ------------- Distribution ------------- count
             < 0 |                                         0
               0 |@@@@@@@                                  525
               1 |@@@@@@@@                                 605
               2 |@@                                       208
               3 |@@@                                      280
               4 |                                         4
               5 |                                         0
               6 |                                         0
               7 |                                         0
               8 |                                         44
               9 |@@                                       161
              10 |                                         2
              11 |                                         0
              12 |                                         0
              13 |                                         4
              14 |                                         0
              15 |                                         29
              16 |@@@@@@@@@@@@@@                           1048
              17 |                                         24
              18 |                                         0
              19 |                                         0
              20 |                                         1
              21 |                                         0
              22 |                                         3
              23 |                                         0

  as_fault
           value  ------------- Distribution ------------- count
             < 0 |                                         0
               0 |@@@@@@@@@@@@@                            4139
               1 |@@@@@@@                                  2249
               2 |@@@@@@@                                  2402
               3 |@                                        594
               4 |                                         56
               5 |                                         0
               6 |                                         0
               7 |                                         0
               8 |                                         189
               9 |@@                                       929
              10 |                                         39
              11 |                                         0
              12 |                                         0
              13 |                                         6
              14 |                                         0
              15 |                                         297
              16 |@@@@                                     1349
              17 |                                         24
              18 |                                         0
              19 |                                         21
              20 |                                         1
              21 |                                         0
              22 |                                         92
              23 |                                         0

The output shows some StarOffice behavior with respect to the virtual memory system. For example, the maj_fault probe didn't fire until a new instance of the application was started. As you would hope, a “warm start” of StarOffice did not result in new major faults. The as_fault output shows an initial burst of activity, latency while the user located the menu to create a new drawing, another period of idleness, and a final burst of activity when the user clicked on a new presentation. The zfod output shows that creating the new presentation induced significant pressure for zero-filled pages, but only for a short period of time.

The next iteration of DTrace investigation in this example would depend on the direction you want to explore. If you want to understand the source of the demand for zero-filled pages, you could aggregate on ustack in a zfod enabling. You might want to establish a threshold for zero-filled pages and use the stop destructive action to stop the offending process when the threshold is exceeded. This approach would enable you to use more traditional debugging tools like truss(1) or mdb(1). The vminfo provider enables you to associate statistics seen in the output of conventional tools like vmstat(1M) with the applications that are inducing the systemic behavior.

24.4. Stability

The vminfo provider uses DTrace's stability mechanism to describe its stabilities, as shown in the following table. For more information about the stability mechanism, see Stability.

Element

Name stability

Data stability

Dependency class

Provider

Evolving

Evolving

ISA

Module

Private

Private

Unknown

Function

Private

Private

Unknown

Name

Evolving

Evolving

ISA

Arguments

Private

Private

ISA