mmap

问题 My understanding of the semantics of volatile in C and C++ is that it turns memory access into (observable) side effects. Whenever reading or writing to a memory mapped file (or shared memory) I would expect the the pointer to be volatile qualified, to indicate that this is in fact I/O. (John Regehr wrote a very good article on the semantics of volatile ). Furthermore, I would expect using functions like memcpy() to access shared memory to be incorrect, since the signature suggests the

问题 Memory mapping a large file on Android in Java works good. But when mapping more than ~1.5GB in total even with multiple mapping calls it fails with: mmap failed: ENOMEM (Out of memory) See the full discussion here. Note: It does not fail on a server Linux. The android:largeHeap="true" is enabled for the application. The following Java code is called a few hundred times requesting ~1MB per call: ByteBuffer buf = raFile.getChannel().map(allowWrites ? FileChannel.MapMode.READ_WRITE :

问题 I was wondering, why should the size of mapped memory being one parameter passed in, since there couldn't more more than one mapping starting from same address (could they ?), why won't linux kernel record both start address, length together, but let userspace program remember them. I mean, why wouldn't it be, just use the start address as primary key to store the information tree. 回答1: One can map , say, 5 pages and later unmap one of them. And information about what pages to unmap is passed

问题 I have a really large file I'm trying to open with mmap and its giving me permission denied. I've tried different flags and modes to the os.open but its just not working for me. What am I doing wrong? >>> import os,mmap >>> mfd = os.open('BigFile', 0) >>> mfile = mmap.mmap(mfd, 0) Traceback (most recent call last): File "<stdin>", line 1, in <module> mmap.error: [Errno 13] Permission denied >>> (using the built in open() works via the python docs example, but it seems to open more than one

问题 I'm trying to find out how to remap memory-mapped files on a Mac (when I want to expand the available space). I see our friends in the Linux world have mremap but I can find no such function in the headers on my Mac. /Developer/SDKs/MacOSX10.6.sdk/usr/include/sys/mman.h has the following: mmap mprotect msync munlock munmap but no mremap man mremap confirms my fears. I'm currently having to munmap and mmmap if I want to resize the size of the mapped file, which involves invalidating all the

问题 I want to enter the pid at the command line and get back the largest contiguous address space that has not been reserved. Any ideas? Our 32 bit app, running on 64 bit RHEL 5.4, craps out after running for a while, say 24 hours. At that time it is only up to 2.5 gb of memory use, but we get out of memory errors. We think it failing to mmap large files because the app's memory space is fragmented. I wanted to go out to the production servers and just test that theory. 回答1: Slighly nicer version

问题 Is there any way in Linux, using c, to generate a diff/patch of two files stored in memory, using a common format (ie: unified diff, like with the command-line diff utility)? I'm working on a system where I generate two text files in memory, and no external storage is available, or desired. I need to create a line-by-line diff of the two files, and since they are mmap 'ed, they don't have file names, preventing me from simply calling system("diff file1.txt file2.txt") . I have file

问题 Is there any way in Linux, using c, to generate a diff/patch of two files stored in memory, using a common format (ie: unified diff, like with the command-line diff utility)? I'm working on a system where I generate two text files in memory, and no external storage is available, or desired. I need to create a line-by-line diff of the two files, and since they are mmap 'ed, they don't have file names, preventing me from simply calling system("diff file1.txt file2.txt") . I have file

问题 If I read and write a single file using normal IO APIs, writes are guaranteed to be atomic on a per-block basis. That is, if my write only modifies a single block, the operating system guarantees that either the whole block is written, or nothing at all. How do I achieve the same effect on a memory mapped file? Memory mapped files are simply byte arrays, so if I modify the byte array, the operating system has no way of knowing when I consider a write "done", so it might (even if that is