OpenSolaris and Linux virtual memory and address space structures

OpenSolaris and Linux virtual memory and address space structures

OpenSolaris and Linux are both popular operating systems that use virtual memory to manage system resources. In this article, we will compare the virtual memory and address space structures of OpenSolaris and Linux.

Segmented address space model

OpenSolaris uses a segmented address space model, where the address space is divided into multiple segments, each of which is used to store a specific type of data. For example, the text segment is used to store executable code, while the data segment is used to store global and static variables. This model allows for more efficient memory allocation and management, as it reduces the fragmentation of memory.

Linux, on the other hand, uses a flat address space model, where the entire address space is treated as a single unit. This model is simpler than the segmented model used by OpenSolaris, but it can lead to more memory fragmentation.

Two-level page table structure

Both OpenSolaris and Linux use a two-level page table structure to translate virtual addresses to physical addresses. In this structure, the virtual address is divided into two parts: the page directory index and the page table index. The page directory index is used to select the page directory, while the page table index is used to select the page table within the selected page directory.

OpenSolaris uses a hierarchical page table structure, where the page tables are organized into a tree structure. This structure allows for more efficient memory management, as only the necessary page tables need to be loaded into memory at any given time.

Linux, on the other hand, uses a flat page table structure, where all of the page tables are stored in a single contiguous block of memory. This structure is simpler than the hierarchical structure used by OpenSolaris, but it can lead to higher memory usage and slower performance.

Demand paging strategy

Both OpenSolaris and Linux use a demand paging strategy to allocate memory. In this strategy, pages are only loaded into memory when they are needed, rather than being loaded in advance. This allows for more efficient use of memory resources, as only the necessary pages are loaded into memory at any given time.

Handling shared memory

OpenSolaris uses a Copy-on-Write (COW) strategy to handle shared memory. In this strategy, when a process requests a copy of a shared memory page, a new copy is not created immediately. Instead, the new process is given a copy of the original page's page table entry, and the original page is marked as read-only. If the new process attempts to modify the page, a new copy of the page is created at that time.

Linux, on the other hand, uses a Shared Virtual Memory (SVM) strategy to handle shared memory. In this strategy, multiple processes can map the same page into their address space. When a process modifies a shared page, the modifications are immediately visible to all other processes that have mapped that page.

Conclusion

In conclusion, both OpenSolaris and Linux use virtual memory and address space structures to manage system resources. OpenSolaris uses a segmented address space model and a hierarchical page table structure, while Linux uses a flat address space model and a flat page table structure. Both operating systems use a demand paging strategy to allocate memory, but they handle shared memory differently: OpenSolaris uses a Copy-on-Write strategy, while Linux uses a Shared Virtual Memory strategy.