wcs@ho95b.UUCP (01/05/84)
The users on my system would like to have 12 MB processes for some
large simulation programs. (I have a VAX 11/780 with 4MB of memory.)
I followed the "Operating/Installing
4.1BSD" instructions, which say to increase MAXTSIZ, MAXDSIZ, and
MAXSSIZ in sys/h/vmparam.h. Whenever a process gets bigger than
about 8 Meg, the system crashes. I'm using interleaved swap to get
2 hp?b sections of swap space, and I don't get an out of swap space
message.
Has anybody successfully done this? What should I check? Any help
will be much appreciated.
Bill Stewart at BTL-Holmdel
ucbvax!ihnp4!ho95b!wcs
decvax!harpo!ho95b!wcs
......!{BTL}!ho95b!wcsMike.Accetta%cmu-cs-ius@sri-unix.UUCP (01/12/84)
Bill, What panic message are you getting? You probably also have to change the definition of NDMAP in h/dmap.h. The setup document mentions this file but neglects to describe what constants to change. We were able to use 12Mb data segment sizes after doubling this constant from 16 to 32. To explain, the paging system allocates chunks of paging space for the data segment geometrically beginning with a size of DMMIN up to a maximum of DMMAX. It stores the pointers to the beginning of each of these chunks in the dm_map array. Paging area memory for a large process would thus get allocated something like this: Chunk Size (sectors) 0 32 \ 1 64 | 2 128 | < .5 Mb 3 256 | 4 512 / 5 1024 \ 6 1024 | 7 1024 | 8 1024 | 9 1024 | 10 1024 | 5.5 Mb 11 1024 | 12 1024 | 13 1024 | 14 1024 | 15 1024 / Which as you can see causes the dm_map array to run out of room slightly before the process size can reach 6Mb. By adding another 16 elements to the the end of the array, you gain 16*.5Mb = 8Mb more process address space for a maximum of slightly under 14Mb (actually the minimum number which you need to increase NDMAP by is more like 12 or 13 for 12Mb data segments depending on how you define MAXDSIZ). When you change this constant it is also advisable to recompile the various user programs (w, ps and pstat are the ones that come to mind immediately) which include this file for examining the user area of a process and for grabbing the command line arguments from the paging area when a process is not resident. - Mike Accetta
thomas@utah-gr.UUCP (Spencer W. Thomas) (01/16/84)
Following up on Mike Accetta's message, I can maybe shed a little more light on the subject of increasing process size. We just did this here, and I operated from two criteria: 1. No user programs should need to be recompiled. 2. System resource usage should not be drastically increased. There are a coupld of parameters you can adjust to get more data space. These are NDMAP and DMMAX. These control the amount of swap space which can be allocated, and which is the limiting factor on process growth. NDMAP says how many entries are in the swap map, there are two of these in the user struct - one for data segment and one for stack segment. DMMAX controls how big the swap segments get. You can increase data size by doubling (and redoubling) DMMAX without changing the size of the U struct (and thus avoiding the necessity of recompiling N user programs). The side effect here is that (internal) fragmentation of the swap area increases. I have seen a recommendation that you have at least 96Mb of swap (3 * 32Mb) for a DMMAX of 4096. Now, obviously this depends on your job mix. Anyway, if you only beat on DMMAX (which is in autoconfig.c, by the way, at least in 4.2), you can get: DFLT> DMMAX=1024 MAXDSIZ=6Mb (approx. (i.e., 12*1024 ...)) DMMAX=2048 MAXDSIZ=11Mb (-32-slop, again) DMMAX=4096 MAXDSIZ=20Mb The effect of DMMAX is that any process larger than DMMAX-32 gets its swap space allocated in DMMAX chunks (so 512kbytes in the distributed system, up to 2Mb with DMMAX=4096). Luckily for us, 11Mb is large enough (for now). =Spencer