kernel_learner wrote: > Is a VMA of a process same as the segments (BSS, Data, > Text seg.. etc.) of that process? A VMA (Virtual Memory Area) is an abstraction that represents part of a process's address space. All memory mapped by a process is represented by some VMA (exactly one VMA, I believe); a single process might have many VMAs covering its address space, but the address ranges represented by those VMAs do not overlap. It's *possible*, but not necessary, that the different segments of a process would be mapped to different VMAs. Basically, what a VMA does is to provide the code to handle page faults for a particular address range. Different kinds of memory objects require different fault handling, so they would be represented by different VMAs. For example, the .text segment of a file would be represented by a VMS whose fault behavior is to page in the proper page from the executable file; but an anonymous (malloc()'d) address range would be represented by a VMA whose fault behavior is to allocate a new anonymous page. > Also could someone please explain the concepts of > segments (BSS, Data, Text etc.)? My OS Fundamentals > are weak about that...and I have never had a > satisfying explaination of it's significance. That kind of segment is just a tool for organizing files. You can more-or-less arbitraily name sections of files with segment names. For example, the Linux kernel puts code that is only used at boot time into a segment called ".init", and discards the .init segment after boot to reclaim the memory. The only reason .init exists is to provide a home for those memory objects the kernel knows it won't need after boot. The other kind of segment is the hardware memory segment, which is supported by Intel processors and, I imagine, others, though in different ways. On Intel, segmentation is a memory abstraction mechanism that sits on top of the paging mechanism and allows a program to map arbitrary contiguous regions of virtual memory using segment descriptors. Linux doesn't use that kind of segment - it just sets up the Intel hardware in such a way that it can use a flat 32-bit virtual address space and ignore the hardware segmentation. Cheers, -- Joe -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
