Hi Stuart - Thanks for your excellent suggestion. I have a couple of comments. * How can we deal with potentially large chunks of memory: I thought we need vmalloc() to allocate large kernel chunks (e.g: >= 10 MB) * I'm concerned about memory limitations since the data is still wired: you're suggesting a mmap-based approach with the user having the possibility to free up the memory with a close() call. In our application, we intend to store each transferred chunk from the kernel in a ring buffer. Thus there is a potential risk to consume all the main memory with a mmap-based approach since the data is still wired. Ideas ? Thanks On Thu, 4 Oct 2001, Stuart Macdonald wrote: > Hi, > > The following works for me: > > 1) User space calls kernel-based function which: > > a) creates a Virtual Memory Area of say 64KB. do_mmap_pgoff() > returning address and then call find_vma() to get the actual vma. > > b) does a pvKernelMem = __get_free_pages(up to 128KB I believe) to > allocate contiguous kernel pages. Note, kmalloc() does not always > end up being page-aligned. Save pvKernelMem for kernel access to shared > memory. > > c) Map the user VMA to the kernel pages using: set_page_reserved() > on all pages then remap_page_range(). > > d) return VMA->vm_start to the user to denote the beginning address > of the shared memory. > > 2) Use memory. Suggest you specify "volatile" on variables utilizing such > shared memory to avoid compiler optimization related > issues. > > 3) Have a "Close" function unmap by using do_munmap() and free kernel pages. > > > Stuart > > - Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ IRC Channel: irc.openprojects.net / #kernelnewbies Web Page: http://www.kernelnewbies.org/
