mmap

I have a Linux application that reads 150-200 files (4-10GB) in parallel. Each file is read in turn in small, variably sized blocks, typically less than 2K each. I currently need to maintain over 200 MB/s read rate combined from the set of files. The disks handle this just fine. There is a projected requirement of over 1 GB/s (which is out of the disk's reach at the moment). We have implemented two different read systems both make heavy use of posix_advise : first is a mmap ed read in which we map the entirety of the data set and read on demand. The second is a read() / seek() based system.

In this thread the OP is suggested to use mmap() instead of shmget() to get shared memory in Linux. I visited this page and this page to get some documentation, but the second one gives an obscure example regarding mmap() . Being almost a newbie, and needing to share some information (in text form) between two processes, should I use the shmget() method or mmap() ? And why? Sergey L. Both methods are viable. mmap method is a little bit more restrictive then shmget , but easier to use. shmget is the old System V shared memory model and has the widest support. mmap / shm_open is the new POSIX

For some reason my mmap failed with an Invalid argument message even though my offset is page aligned. Page size is 4096 bytes. Also CONFIG_STRICT_DEVMEM is disabled, i.e. I can access memory above 1MB. Here is my code: void *mmap64; off_t offset = 0x000000d9fcc000; int memFd = open("/dev/mem", O_RDWR); if (-1 == memFd) perror("Error "); mmap64 = mmap(0, getpagesize(), PROT_WRITE | PROT_READ, MAP_SHARED, memFd, offset); if (MAP_FAILED == mmap64) { perror("Error "); return -1; } Can someone explain why this is happening? EDIT Here is the strace of my code execve("./to_phys_test", ["./to_phys

Has anybody succeeded in mmap'ing a /proc/pid/mem file with Linux kernel 2.6? I am getting an ENODEV (No such device) error. My call looks like this: char * map = mmap(NULL, PAGE_SIZE, PROT_READ, MAP_SHARED, mem_fd, offset); And I have verified by looking at the /proc/pid/maps file while debugging that, when execution reaches this call, offset has the value of the top of the stack minus PAGE_SIZE. I have also verified with ptrace that mmap is setting errno to ENODEV. ephemient See proc_mem_operations in /usr/src/linux/fs/proc/base.c : /proc/.../mem does not support mmap . 来源： https:/