-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Chuck,
Caldarale, Charles R wrote: >> From: Christopher Schultz [mailto:[EMAIL PROTECTED] >> Hmm.... perhaps I have a virtual memory limit. I have 1GB >> of physical RAM. While allocating a 3GB heap is pretty >> stupid for me, I still ought to be able to do it. > > If your OS will allow, yes you should. You may need to increase your > swap file space, and you may burn out your hard drive thrashing pages in > and out. I think I just did using this little beauty: #include <stdio.h> #include <stdlib.h> /* 50 MB */ #define CHUNK_SIZE (1024 * 1024 * 50) int main(int argc, char *arvg[]) { void *ptr; int i; unsigned long bytes = 0l; for( ; ;) { ptr = calloc((size_t)CHUNK_SIZE, (size_t)1); bytes += CHUNK_SIZE; /* write to our new memory */ for(i=0; i<CHUNK_SIZE; ++i) *((char*)ptr + i) = (char)i; printf("Heap has now allocated %lu bytes\n", bytes); if(bytes > (unsigned long)(1024 * 1024 * 1024 * 3.9)) fgetc(stdin); } } Oddly enough, it stopped printing stuff out after 1677721600 bytes. Before I added the "write to our memory" loop, it ran very quickly and completed (well, the fgetc was to pause so I could observe memory usage). I guess that Linux not only does optimistic malloc, but also optimistic calloc as well. I had hoped that zeroing-out the memory would count as a "write", but apparently it does not. Anyhow, I believe I'm running out of swap in this situation. I think I only have a gig of swap on this development machine, which means that I have a hard limit of 2GB anyway. Anyone care to try this program on their many-gigabyted development box? >> My ulimit man page sucks. Anyone know how to change the virtual memory >> limits on Linux 2.6? > > Here's a link for SUSE: > http://en.opensuse.org/SDB:Ulimit_for_Protection_Against_%22Out_of_memor > y%22 Thanks for the link. Probably won't help me with my 1GB of virtual memory. Heh. >> If the heap can grow and shrink, then how can the VM hope to >> get one bigass memory chunk for the heap? > > The JVM reserves - but does not commit - the -Xmx size during > initialization. If that's not available, the JVM won't start. Once > allocated, commits and decommits occur to expand and shrink the in-use > size. Aah, I see. So the heap is actually fixed (to the maximum value) but the internal management of the heap will fluctuate. >> Still, the only remaining reason that 2GB+ wouldn't work is >> because of a (potential) 2GB contiguous memory allocation >> restriction. I see no such restriction in the malloc or brk >> man pages on my system. What gives? > > Those are typically generic descriptions aimed at application > programmers. What we're discussing here is OS internals, and you'll > rarely see those documented anywhere. If you're lucky, the OS vendor > will have such limitiations squirreled away in some appendix to its > installation guide. Well, since this is Linux, there really isn't an operating guide. I suppose the man pages couldn't include that information, anyway, since it's a kernel setting chosen at kernel build-time. But, the GNU malloc man page does describe the "OOM killer" behavior exhibited by Linux kernels (under certain configurations). I had expected that this other issue might have been covered as well. I still can't find any documentation about a 2GB contiguous allocation limit for Linux anywhere. Is this just "common knowledge" that nobody has bothered to verify? I mean, this is entirely academic at this point, but it would be nice to actually know the truth instead of everyone just posting their 5th-hand repeated guesses. - -chris -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFF+BYu9CaO5/Lv0PARAhZGAKC1u/BtCWSdI6eIGeBuH5qXtD1JZQCfTTPw DaJRF41SVbVFJMBgfozB3lA= =qd9B -----END PGP SIGNATURE----- --------------------------------------------------------------------- To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
