> I am trying to understand the kernel page frame reclaiming > mechanism, but one thing's bothering me: > How does the kernel 'know' which anonymous pages to evict? In the LRU > scheme, 'referenced/used' information for each page is required > (AFAIK). But anonymous pages can be used by user processes 'at any > time' without the kernel knowing about it. a. Every anonymous page starts out referenced. b. The process address space is described by the mm_struct, which has different regions defined by vm_area_struct(vma). c. A region may represent the process heap for use with malloc(), a memory mapped file such as a shared library or a block of anonymous memory allocated with mmap(). d. Every physical page(atleast those directly mapped into kernel linear address space) have a struct page associated with it. e. Now struct page has a struct address_space *mapping in it. In mapping, if low bit clear, points to inode address_space else if page mapped as anonymous low bit is set. f. Lets say low bit is set, then this mapping points to a anon_vma struct. This anon_vma is linked list of all vma's that have reference to that page. If the kernel needs to unmap a anonymous page, it must follow this linked list and examine every VMA it finds. Once the page is unmapped from every page table found from each vma(vma-->mm_struct-->pgd), it can be freed. -syed _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
