how to traverse page cache tree (radix tree) of a file address space in linux kernel - linux

Question

I need to get page-cache statistics of an open file. There is a address_space pointer(f_mapping) in file struct which in turn has the root of the radix tree called page_tree. I need to traverse that tree to get information about all the cached pages for that open file.
There are some functions like radix_tree_for_each_chunk(to iterate over chunks), radix_tree_for_each_chunk_slot (to iterate over slots in one chunk) etc, using these the functionality can be achieved. I am unsure about the proper use (arguments) of the same. It would be helpful if any example is posted.

Answer 1

I figured it out from Linux kernel source code.
struct file *file = filp_open("filename",O_RDONLY,0);
struct address_space *file_addr_space = file->f_mapping;
if(file_addr_space==NULL){
printk("error")
}
struct radix_tree_root file_page_tree_root = file_addr_space->page_tree; //contains all pages in page cache
struct radix_tree_iter iter;
void **slot;
int num_dirty = 0;
radix_tree_for_each_slot(slot,&file_page_tree_root,&iter,0){
struct page *page = radix_tree_deref_slot(slot);
if(page!=NULL){
//printk("information about page");
}
}