The phaseout of the mmap() file operation in Linux
17 hours ago
- #Memory Management
- #System Calls
- #Linux Kernel
- The mmap() file operation was introduced in Linux kernel version 0.98.2 in 1992, evolving over time to its current prototype.
- The mmap() method allows drivers to set up memory mappings but has significant issues, including complex cleanup on failure and direct access to core memory-management structures.
- A new API, mmap_prepare(), was introduced in kernel 6.17 to replace mmap(), aiming to reduce cleanup complexity and limit driver access to memory-management structures.
- mmap_prepare() operates earlier in the mapping process and uses the vm_area_desc structure to provide necessary information to drivers without exposing the VMA directly.
- Further enhancements to mmap_prepare() include the mmap_action structure, enabling drivers to request specific post-VMA setup actions like remapping memory ranges.
- The new API supports callbacks for success and error handling, improving efficiency and error management for memory mappings.
- Despite progress, converting hundreds of existing mmap() implementations to the new API will take time, with ongoing development and review.