Re: Q alloc SPool Help BINGO!!!!!!! - now we are on to something! >The size of your dump area, is determined by the memory locations that >CP has "ever" used. For example, when CP needs 10 pages from the >Dynamic Paging Area, if it never touched those pages before, you dump >file expand by those 10 pages. When CP releases those pages, those >pages are not, repeat "NOT" released from your dump file requirements. >So, if the next time CP needs a few pages, if it uses the pages it used >before, those pages have already been marked as pages to be written to >the dump file, in case of an abend. However, if they are never befored >allocated pages to CP, even if there has been freed pages before, your >dump area will expand to include those pages in the dump in case of a CP >abend.
As I've explained here several times, CP does increase the amount of dump space allocated when it needs to, but not on a page by page basis. Beginning in z/VM 4.4.0, the amount of dump space allocated is reduced when appropriate. This is how it works: Before z/VM 4.4.0: 1) During CP initialization and whenever a SET DUMP DASD command is issued, CP allocates dump space based on the number of CP pages in use at that point in time. CP adds 12.5% to the number of pages in use and allocates that many spool pages for dump. 2) Each time CP allocates a new page, the number of pages in use is checked to see if it has reached the total number of spool pages allocated for dump. If it has, CP releases the dump space it has allocated, adds 12.5% to the current number of CP pages in use, and re-allocates that many spool pages for dump. Dump space allocation is increased as needed but never reduced unless SET DUMP is issued. In z/VM 4.4.0 and later: 1) During CP initialization and whenever a SET DUMP DASD command is issued, CP allocates dump space based on the number of CP pages in use at that point in time. CP adds 12.5% to the number of pages in use and allocates that many spool pages for dump. CP also computes and saves a threshold value which is 25% below the number of pages in use. 2) Each time CP allocates a new page, the number of pages in use is checked to see if it has reached the total number of spool pages allocated for dump. If it has, releases the dump space it has allocated, adds 12.5% to the current number of pages in use, and re-allocates that many spool pages for dump. CP also re-computes -25% threshold value. If the number of CP pages in use is reduced to the point that it reaches the -25% threshold value, CP releases the dump space it has allocated, adds 12.5% to the current number of pages in use, and re-allocates that many spool pages for dump. A new -25% threshold is also computed based on the current number of pages in use. >If your dump file is allocated from spool and spool is full and CP >tries to allocate a "never before allocated to CP" page? It can't >expand the dump dataset and CP abends. >So, indirectly, if you don't have a "dump" area, equal in size to your >main memory (up to 2 GB) in an area of type "dump" (not spol), you are >subject to a CP abend when spool file fills. NO! ALL dump space is allocated from spool. There is a DUMP operand on the CP_OWNED system configuration file statement which allows you to reserve all of the allocated spool (SPOL) space on particular volume(s) for dumps. CP does NOT abend if there is not enough spool space available to allocate a dump. It will simply turn dump off, and a message is sent to the operator indicating that dump is off because there is not enough space for it. >Apparently the 2 GB max will still be the case with z/VM 5.2. CP will >still allocate below the line. It is I/O that now can be moved above >the line with z/VM 5.2. Dumps will be larger in 5.2.0, and can be larger than 2 GB due to the increased size of the frame table and other control structures. But it will not be as large as the amount of storage you might have on your system. The rule of thumb is to allow twice as much space for dumps in 5.2.0 than you did in 5.1.0. John Franciscovich z/VM Development
