Messages in this thread | | | Date | Mon, 13 Mar 2000 03:54:31 -0800 (PST) | From | David Whysong <> | Subject | Re: Overcommitable memory?? |
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On 13 Mar 2000, Rask Ingemann Lambertsen wrote: > >Apps would be told that the system is out of memory instead of just >getting a SIGKILL'ed out of the blue sky. Apps getting NULL from >malloc() can react appropriately, such as saving your files to disk, >trying again a little later or just exiting if that is acceptable for >what the app was doing. Apps getting SIGKILL will take your unsaved work >with them in the fall.
Ok, so my big gravitational simulation gets NULL from malloc and decides to save it's work and exit. Uh-oh, time to demand-load a page of executable code that had been discarded, so we can save the data. Hmm, but we're out of memory...
Even if that succeeds, or there is a foolish "no overcommit" policy, we need disk buffers. What if the program was told to save output to a SCSI device, and the kernel needs to load the driver module? We're out of memory! Even if we all build non-modular kernels, the kernel does some dynamic memory allocation.
As for "trying again a little later", that leaves you with an unresponsive and unusable system in many cases.
And please explain why my simulation -- that may have started many weeks (or months) ago -- should "just exit" because some random 5-minute old Mathematica process went and allocated half a gigabyte of memory?
Dave
David Whysong dwhysong@physics.ucsb.edu Astrophysics graduate student University of California, Santa Barbara My public PGP keys are on my web page - http://www.physics.ucsb.edu/~dwhysong DSS PGP Key 0x903F5BD6 : FE78 91FE 4508 106F 7C88 1706 B792 6995 903F 5BD6 D-H PGP key 0x5DAB0F91 : BC33 0F36 FCCD E72C 441F 663A 72ED 7FB7 5DAB 0F91
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