Reverse mapping of anonymous pages

The establishment process of reverse mapping

When passed fork When creating a subprocess , In this process, the infrastructure of reverse mapping will be established , Specific in
kernel_clone -》 copy_mm -》 dup_mm -》 dup_mmap in ：

1. dup_mmap Each of the parent processes vma Copy one to the child process , This is just an example of copying a vma The situation of , As shown in the figure above, the neutron process vma
2. anon_vma_clone To create a child process avc01, It is also associated with the parent process av0 And subprocess vma Establishing correlation , That is, to join the child process vma Linked list , Connect to the parent process at the same time av0 Red and black trees , It is added to the parent process as a representative of the child process av0 Red and black trees , When the parent process looks for the reverse mapping in the future , Will traverse this red black tree , And get vma, When a child process is reverse mapped , Just traverse yourself av Red and black trees , This improves efficiency ;
3. adopt anon_vma_alloc Assign your own to the child process av1, It is related to the parent process av0 Form a father son relationship ;
4. adopt anon_vma_chain_alloc Assign your own to the child process avc1;
5. adopt anon_vma_chain_link Set up a subprocess av1, avc1, vma The associated

notes ： Above av by strucdt anon_vma, avc by anon_vma_chain

Reverse mapping lookup process

1. adopt page Of mapping Field found av;
2. Traverse av Red and black trees , Find all avc;
3. adopt avc Find the corresponding vma, And pass vma find vma_start, And vm_mm And find out pgd;
4. adopt page->index and vma_start Get the starting address of the virtual page ;
5. Through the starting address of the virtual page and pgd find pte

Reference documents

《Linux Kernel depth parsing 》
《 In depth understanding of Linux Kernel reverse mapping mechanism 》