Hard VS. Soft Page Faults

[Chaim Budnick]

Is there a way using MONITOR to be able to differentiate between hard/soft page faults?

Chaim

[Uwe Zessin · Accepted solution]

Yes.
http://h71000.www7.hp.com/doc/72final/6491/6491pro_006.html#index_x_227

And when using "MONITOR SYSTEM", there is a vertical bar (|) that separates the hard and soft faults.

[Chaim Budnick]

Which side is hard and which is soft?

Chaim

[Uwe Zessin]

http://h71000.www7.hp.com/doc/732FINAL/6048/6048pro_004.html#index_x_1494

""In the Page Fault segment, the page read I/O rate is indicated by a vertical bar. The bar provides a visual estimate of the proportion of the total page fault rate that caused read I/O operations (the hard fault rate). The hard fault rate appears to the left of the bar.""

[faris_3]

Hi,

- on the monitor page screen the 2nd to 5 th line are hard faults
the 5 next lines are soft faults
(free list to Wrt in Progress)

- on the monitor system screen
under page fault Rate, a vertical bar separates hard faults (left) from soft faults.

hth,
HF

[Chaim Budnick]

Thanks for all the replies !!

There are a large number of page faults (between 300 - 1000), most of which (probably around 90%) are SOFT.

Can this magnitude of soft PFs seriously affect performance?

Chaim

P.S. This is a DSM application

[Uwe Zessin]

It depends on the hardware whether it has enough horse power - 300-1000 does not sound much to me. Soft faults means just shuffling a few pointers around, so this is not has 'bad' has hard faulting. Remember that you will never be able to eliminate all faults - VMS uses the page fault handler to get images into memory - there is not separate program loader.

[Wim Van den Wyngaert]

Chaim,

Try to find out which process is doing it (mon proc/topf). It might be that the working set is too small for what the process is doing or that lots of image activations are done. WS : increase quotas, image act. : try installing them.

Database servers with bad WS quotas can pagefault like crazy.

Wim

[Hein van den Heuvel]

Chaim,

If you need further help, then please attach some sample monitor output in a text files. Concreate numbers help discussing this.

What Wim refers to is notably Global Valid Pagefaults. Those mean that a shared-library/share-buffer-page was in memory, but the process could not 'look' at it yet due to restricted wsquota (or because it had never tried to look at it so far). Increasing WS will not directly increase physical memory usage for this while it will reduce this soft pagefault overhead. (indirectly memory usage may creep up, if for example SORT sees the extra WS and uses it).
A similar reasoning applies to free/modified page list soft faults. Just increase WS!?

If this is an Oracle DB application, you may want to consider RESERVEED MEMORY allowing the SGA to be mapped with huge pages and with no WS charge/usage.


Hope this helps some,
Hein.

[Willem Grooters]

If a program initiliazes (fills) a (large) array with values the wrong way, it can introduce a huge pagefaultrate as well - soft, mostly, but nevertheless choking the system for some time. "the wrong way" depends on the language. IIRC, a FORTRAN will store arrays column by column, so filling it is best done column-by-colunm; doing it row-by-row may introduce huge pagefault-rate, if the array is large enough, it may be 1 pagefualt for each cell)