Understanding Linux /proc/id/maps

[http://stackoverflow.com/questions/1401359/understanding-linux-proc-id-maps]

Q:I am trying to understand my embedded linux application's memory use. The /proc/pid/maps utility/file seems to be a good resource for seeing the details. Unfortunately I don't understand all the columns and entries.

Is there good resource/documentation for the proc//maps utility/file?

What does the anonymous inode 0 entries mean? These seem to be some of the larger memory segments.::

A:

Each row in /proc/$PID/maps describes a region of contiguous virtual memory in a process or thread. Each row has the following fields: address - This is the starting and ending address of the region in the process's address space permissions - This describes how pages in the region can be accessed. There are four different permissions: read, write, execute, and shared. If read/write/execute are disabled, a '-' will appear instead of the 'r'/'w'/'x'. If a region is not shared, it is private, so a 'p' will appear instead of an 's'. If the process attempts to access memory in a way that is not permitted, a segmentation fault is generated. Permissions can be changed using the mprotect system call. offset - If the region was mapped from a file (using mmap), this is the offset in the file where the mapping begins. If the memory was not mapped from a file, it's just 0. device - If the region was mapped from a file, this is the major and minor device number (in hex) where the file lives. inode - If the region was mapped from a file, this is the file number. pathname - If the region was mapped from a file, this is the name of the file. This field is blank for anonymous mapped regions. There are also special regions with names like [heap], [stack], or[vdso]. [vdso] stands for virtual dynamic shared object. It's used by system calls to switch to kernel mode. Here's a good article about it. You might notice a lot of anonymous regions. These are usually created by mmap but are not attached to any file. They are used for a lot of miscellaneous things like shared memory or buffers not allocated on the heap. For instance, I think the pthread library uses anonymous mapped regions as stacks for new threads. share | improve this answer edited  Dec 8 '10 at 21:38 pts 9,330 3 29 68 answered  Sep 9 '09 at 19:30 Jay Conrod 10.3k 5 42 77

Yes the pthreads are allocating 8Mb blocks for a stack with a smaller section for stack overflow detection(i think). So each pthread created, by default, allocates an inode 0 memory region of 8Mb and a inode 0 region of 4Kb. –  simon  Sep 10 '09 at 17:13