On 16.05.23 07:29, Huang Ying wrote:
The general rule to use a swap entry is as follows. When we get a swap entry, if there isn't some other way to prevent swapoff, such as page lock for swap cache, page table lock, etc., the swap entry may become invalid because of swapoff. Then, we need to enclose all swap related functions with get_swap_device() and put_swap_device(), unless the swap functions call get/put_swap_device() by themselves. Add the rule as comments of get_swap_device(), and cleanup some functions which call get/put_swap_device(). 1. Enlarge the get/put_swap_device() protection range in __read_swap_cache_async(). This makes the function a little easier to be understood because we don't need to consider swapoff. And this makes it possible to remove get/put_swap_device() calling in some function called by __read_swap_cache_async(). 2. Remove get/put_swap_device() in __swap_count(). Which is call in do_swap_page() only, which encloses the call with get/put_swap_device() already. 3. Remove get/put_swap_device() in __swp_swapcount(). Which is call in __read_swap_cache_async() only, which encloses the call with get/put_swap_device() already. 4. Remove get/put_swap_device() in __swap_duplicate(). Which is called by - swap_shmem_alloc(): the swap cache is locked. - copy_nonpresent_pte() -> swap_duplicate() and try_to_unmap_one() -> swap_duplicate(): the page table lock is held. - __read_swap_cache_async() -> swapcache_prepare(): enclosed with get/put_swap_device() already. Other get/put_swap_device() usages are checked too.
I suggest splitting this patch up into logical pieces as outlined here by you already.
-- Thanks, David / dhildenb
