Everhart, Glenn
From:	music@erich.triumf.ca
Sent:	Monday, December 14, 1998 1:56 PM
To:	Info-VAX@Mvb.Saic.Com
Subject:	Deallocating pages in the pagefile
       The following program is a test program used to consume
       (allocate) pagefile and then try to free it up (deallocate). 
       Unfortunately, it appears that after the  pages have been
       deallocated,  the count of the pages in use has not actually been
       updated (as known by the process's pagefile quota in use). 
       Apparently,  the pagefile is really freed up when the image is
       run down.  This implies that the operating system can free up the
       pagefile without terminating the process but just by image
       rundown, so it seems reasonable that the image should be able to
       also force the pages to be freed up (as known by the process's
       pagefile quota in use). In fact,  I am rather surprised that this
       does not happen automatically when the pages are deallocated. 
       The impact of this behavior for some images is rather
       catastrophic.  For example,  an image that may run continuously
       (for weeks on end) may occasionally need a lot of memory but only
       for a short time.  If there are a lot of these images and they do
       not free up their portion of the pagefile when they deallocate
       memory then the overall pagefile must be MUCH larger than it
       actually needs to be if the pages were freed up.

       AMDS (avail) was used to monitor the pagefile use for the process
       as the image was run and then stopped.

       Is there a way to free up the deallocated pages in the pagefile
       without stopping the image?

	program test

	implicit    none
        integer*4   alloc_num, max_alloc_num
        parameter   (max_alloc_num = 100)
        integer*4   base_address(max_alloc_num)
        integer*4   num_of_pages/1000/, dealloc_num

        do 100 alloc_num = 1, max_alloc_num
	type *, 'allocation # ', alloc_num
        call lib$get_vm_page ( num_of_pages, base_address(alloc_num))
100     continue

        pause

        do 200 dealloc_num = 1, max_alloc_num
	type *, 'deallocation # ', dealloc_num
        call lib$free_vm_page ( num_of_pages, base_address(dealloc_num))
200     continue

        pause

	stop
	end


 Fred W. Bach ,    Operations Group     |  Internet: music@triumf.ca
 TRIUMF  (Canada's National Meson Lab.) |  Voice:  604-222-1047 loc 6278/6327
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