On Sun, Sep 16, 2012 at 9:21 PM, Mark Jackson <[email protected]> wrote: > Apologies if this is the wrong place to post this query. Please feel free > to redirect me to the correct place. > > I have come across a weird (but documented [1]) "feature" of mmap(), which > is:- > > "The mmap()function adds an extra reference to the file associated with the > file descriptor fildeswhich is not removed by a subsequent close() on that > file descriptor. This reference is removed when there are no more mappings > to the file." > > In my embedded application, this is resulting in the consumption of > available file descriptors. > > As an example I wrote the following test running on Ubuntu 11.04 64bit. > > #include <fcntl.h> > #include <errno.h> > #include <stdio.h> > #include <sys/mman.h> > > #define FRAM_SIZE (64 * 1024) > #define FRAM_BASE_ADDRESS 0x00000000 > > int main(int argc, char **argv) > { > int i; > for (i = 0; i < 5000; i++) > { > // open the fram device > int m_fdFram = open("/dev/mem", O_RDWR | O_SYNC); > if (m_fdFram < 0) > { > printf("could not open /dev/mem, exiting with errno %d\n", > errno); > return 0; > } > > // map the device to memory > char *m_pFram = (char *)mmap( 0, > FRAM_SIZE * sizeof(unsigned short), > PROT_READ | PROT_WRITE, > MAP_SHARED, > m_fdFram, > FRAM_BASE_ADDRESS); > if ((int)m_pFram == -1) > { > close(m_fdFram); > m_fdFram = -1; > printf("could not mmap, exiting with errno %d\n", errno); > return 0; > } > > // now remove the mapping > if (m_pFram) > munmap(m_pFram, FRAM_SIZE);
You unmap less memory than you map... -- Thanks, //richard -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
