CODEWITHSUNDEEP
linuxoperating-system
Vindhya G
Vindhya G

Reputation: 1369

virtual address for processes having more memory than 4GB

If a process uses 6GB of memory and pointers are of 32 bits,how can addressing be done for 2GB above 4GB since pointers hold virtual addresses in linux?

Is running on the 64 bit only solution?Sorry for naive question

Upvotes: 0

Views: 689

Answers (2)

Basile Starynkevitch
Basile Starynkevitch

Reputation: 1

As I said in a comment, running on 64 bits is the practical solution. You really don't want to munmap then mmap again large segments on temporary files.

You could change your address space during runtime, but you don't want to do that (except when allocating memory, e.g. thru malloc, which may increase the available space thru mmap).

Changing the address space to get the illusion of a huge memory is a nightmare. Avoid that (you'll spend months on debugging hard to reproduce bugs). In the 1960-s IBM 1130 did such insane tricks.

Today, computers are cheaper than developer's time. So just buy a 64 bits processor with 8Gb (gigabytes) RAM.

Several 32 bits processors with the PAE feature are able to use more than 4Gb RAM, but each process only see at most 4Gb (in reality 3Gb) of virtual memory.

It is related to virtual memory, not to Intel-specific segmentation. Current Linux (and others) operating system use a flat memory model even on Intel processors.

Upvotes: 1

Benny
Benny

Reputation: 4321

Completing Basile's answer, most architectures have extended the physical address-space to 36-bit (see Intel's PSE, PowerPC's Extended Real Page Number, ...). Therefore, although any process can only address 4GB of memory through 32 bits pointers, two differents process are virtually able to address different 4GB of a 64GB physical memory address space. This is a way for a 32bit' OS to address up to 64GB of memory (for instance, 32GB for Windows 2003 Server).

Upvotes: 2

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