> A task that has been running for some time may (will!) have fragemented > Virtual Address space. A new task should not (though it is possible, say, > if a shared library has been set to load at a poorly chosen fixed address). This type of fragmentation is not caused by malloc. It is most typically the result of the dynamic library loader, which does not use malloc, but instead uses mmap directly. Usually once the program has been fully loaded and initialized this memory will not change as the program continues to run, and likewise will be released (to that process) when it terminates. However your observation is correct that a fixed-address library may subdivide the available virtual memory address into smaller regions. If you're latter trying to malloc a very large segment that's close the the virtual memory size (depends on 32 or 64 bit), then you can run into problems. You can get a hint as to where a process is using memory by looking at /proc/12345/maps (where 12345 is the process id of your mysqld process). It should be easy to see if a library is responsible for splitting your memory into too-small chunks. Also the file /proc/12345/status might have useful information. Check out the man page for ld.so(8), as there are environment variables you can set to get debugging information out of the process loading stage. Also, if you've disabled your overcommit per above, then make sure you have enough paging/swapping space available or that can also cause memory allocations to fail. It should be at least as large as the amount of physical memory. cat /proc/swaps Although I don't think mysql uses it, SystemV style shared memory is not usually released when a program terminates, until it's released manually. Run "ipcs -a" as root to see what's there. > When a task exits, all its (non-shared) memory is returned to the OS. > Shared memory is returned to the OS when the last sharing task exits. Except for SystemV style shared memory which is not released. Also, when memory that once held shared libraries is freed, it is made available for re-use, but it's not immediately flushed, under the anticipation that the same library will be reloaded soon. Note that under some other OSs, like AIX, shared libraries once loaded tend to stay in memory and it's resources unavailable to other things. Linux is more forgiving. Deron Meranda
