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Ask the Wizard Questions

Scheduling: RWMPB

The Question is:

When running a Program it is seen to go into a RWMPB
State sometimes. Not a Serious problem but what is RWMPB
and why might you get it ?

The Answer is:

    The meaning of RWMPB is Resource Wait - Modified Page-writer Busy.  A
    process is placed into this state by the pager when a process attempts
    to displace a page from its working set to the modified list when the
    size of the modified list has already reached MPW_WAITLIMIT.

    The process is removed from this state once the Modified Page-writer
    has written down the modified list to MPW_LOWAITLIMIT.

    The occurrence of this state can be reduced by encouraging the modified
    page-writer to write pages a little more frequently and by allowing
    processes to continue processing for some time after the modified list
    exceeds MPW_HILIMIT.

    To accomplish this, select a value for MPW_WAITLIMIT of 4 to 8 times
    8)*MPW_WRTCLUSTER).  If MPW_WAITLIMIT or MPW_HILIMIT is already at it
    maximum (65535) then set MPW_HILIMIT to 4 to 8 times MPW_WRTCLUSTER
    less than MPW_WAITLIMIT (65535 - (4 or 8)*MPW_WRTCLUSTER).

    This occurrence of this wait state can be greatly exacerbated in SMP
    systems when there is not a buffer of allowable pages on the modified
    list when the modified page-writer begins writing pages (when the
    number of pages exceeds MPW_HILIMIT).

    By allowing a buffer of pages between MPW_HILIMIT and MPW_WAITLIMIT,
    the modified page-writer can begin writing pages sooner (when the list
    exceeds MPW_HILIMIT) and when processes begin being placed in a wait
    state (MPW_WAITLIMIT).  On SMP systems, the buffer also allows
    processes busy on other processors to continue processing and pushing
    some pages from their working sets while the modified page-writer is
    busy pushing pages to the page files.

    If after this change the resource waits persist, also ensure that your
    page files are not filling up or that there is not contention for
    paging disk or the paths to the disk containing the page files.