{
  "id": 345237,
  "title": "Linux Memory Region Data Structures",
  "url": "https://urgent.news/2026/08/09/linux-memory-region-data-structures",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-08-09T04:30:00.000Z",
  "source": {
    "name": "Dev.to",
    "slug": "dev-to",
    "url": "https://dev.to/kai-wen-the-parrot/linux-memory-region-data-structures-1dnl"
  },
  "original_language": "en",
  "account": "The memory descriptor, known as mm_struct, holds crucial data about a process's address space, including the amount of memory it occupies. Within this structure, there is a linked list of Virtual Memory Areas (VMAs) represented by vm_area_struct. This list is accessed via the mmap field of mm_struct, which points to the first memory region in the linked list. Each VMA contains a pointer to the subsequent memory region (vm_next), enabling the kernel to traverse all virtual memory regions belonging to the process. The total number of VMAs owned by the process is recorded in the map_count field. The Linux kernel sets a default maximum of 65,536 VMAs, although most processes utilize far fewer.\n\nWhen a process frequently allocates memory—through methods like malloc(), shared libraries, or memory-mapped files—it may accumulate a large number of VMAs, ranging from hundreds to thousands. Traversing the linked list to locate a specific memory region requires examining each node sequentially, resulting in a time complexity of O(n). To expedite lookup processes, Linux employs a red-black tree, an advanced data structure that maintains balance. This tree is embedded within each VMA as a vm_rb field of type struct rb_node. The root of the tree is stored in the process's memory descriptor (mm_rb). The tree is organized by the starting virtual address (vm_start) of each memory region, with smaller addresses placed in the left subtree and larger addresses in the right subtree. The red-black tree upholds balance through several properties: nodes are colored either red or black, the root node is always black, red nodes cannot have consecutive red children, and every path from a node to a null descendant leaf contains the same number of black nodes. This ensures the tree's height remains at most 2 log₂(n + 1), allowing for efficient searching, inserting, and deleting of VMAs in O(log n) time.\n\nIn recent Linux versions (starting from 6.1), the kernel has replaced both the linked list (mmap) and red-black tree (mm_rb) for managing VMAs with a single data structure called the Maple Tree. The mm_struct now includes a single field, struct maple_tree mm_mt. The Maple Tree addresses the limitations of its predecessors by storing multiple memory regions within each node, akin to a B-tree. This allows for efficient searching, insertion, and deletion of VMAs while maintaining a time complexity of O(log n). However, the Maple Tree offers lower constant overhead and superior real-world performance compared to the previous implementation.",
  "summary": "The memory descriptor ( mm_struct ) maintains information about a process's address space (current memory it owns). One of its members is a linked list of Virtual Memory Areas (VMAs) , represented by vm_area_struct . The memory descriptor ( mm_struct ) contains a field named mmap , which points to the head of the linked list of Virtual Memory Areas (VMAs) . Each VMA ( vm_area_struct ) contains a…",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}